iptables can use extended packet matching modules with the -m or
--match options, followed by the matching module name; after these,
various extra command line options become available, depending on the specific
module. You can specify multiple extended match modules in one line, and you
can use the -h or --help options after the module has been
specified to receive help specific to that module. The extended match modules
are evaluated in the order they are specified in the rule.
If the -p or --protocol was specified and if and
only if an unknown option is encountered, iptables will try load a match
module of the same name as the protocol, to try making the option
available.
This module matches packets based on their address type. Address types
are used within the kernel networking stack and categorize addresses into
various groups. The exact definition of that group depends on the specific
layer three protocol.
The following address types are possible:
- UNSPEC
- an unspecified address (i.e. <IP_ADDRESS>)
- UNICAST
- an unicast address
- LOCAL
- a local address
- BROADCAST
- a broadcast address
- ANYCAST
- an anycast packet
- MULTICAST
- a multicast address
- BLACKHOLE
- a blackhole address
- UNREACHABLE
- an unreachable address
- PROHIBIT
- a prohibited address
- THROW
- FIXME
- NAT
- FIXME
- XRESOLVE
- [!] --src-type type
- Matches if the source address is of given type
- [!] --dst-type type
- Matches if the destination address is of given type
- --limit-iface-in
- The address type checking can be limited to the interface the packet is
coming in. This option is only valid in the PREROUTING,
INPUT and FORWARD chains. It cannot be specified with the
--limit-iface-out option.
- --limit-iface-out
- The address type checking can be limited to the interface the packet is
going out. This option is only valid in the POSTROUTING,
OUTPUT and FORWARD chains. It cannot be specified with the
--limit-iface-in option.
This module matches the parameters in Authentication header of IPsec packets.
- [!] --ahspi spi[:spi]
- Matches SPI.
- [!] --ahlen length
- Total length of this header in octets.
- --ahres
- Matches if the reserved field is filled with zero.
This module matches the SPIs in Authentication header of IPsec packets.
- [!] --ahspi spi[:spi]
Match using Linux Socket Filter. Expects a path to an eBPF object or a cBPF
program in decimal format.
- --object-pinned path
- Pass a path to a pinned eBPF object.
Applications load eBPF programs into the kernel with the bpf()
system call and BPF_PROG_LOAD command and can pin them in a virtual
filesystem with BPF_OBJ_PIN. To use a pinned object in iptables, mount the
bpf filesystem using
- mount -t bpf bpf ${BPF_MOUNT}
then insert the filter in iptables by path:
- iptables -A OUTPUT -m bpf --object-pinned ${BPF_MOUNT}/{PINNED_PATH} -j
ACCEPT
- --bytecode code
- Pass the BPF byte code format as generated by the nfbpf_compile
utility.
The code format is similar to the output of the tcpdump -ddd
command: one line that stores the number of instructions, followed by one
line for each instruction. Instruction lines follow the pattern 'u16 u8 u8
u32' in decimal notation. Fields encode the operation, jump offset if true,
jump offset if false and generic multiuse field 'K'. Comments are not
supported.
For example, to read only packets matching 'ip proto 6', insert
the following, without the comments or trailing whitespace:
- 4 # number of instructions
48 0 0 9 # load byte ip->proto
21 0 1 6 # jump equal IPPROTO_TCP
6 0 0 1 # return pass (non-zero)
6 0 0 0 # return fail (zero)
You can pass this filter to the bpf match with the following
command:
- iptables -A OUTPUT -m bpf --bytecode '4,48 0 0 9,21 0 1 6,6 0 0 1,6 0 0 0'
-j ACCEPT
Or instead, you can invoke the nfbpf_compile utility.
- iptables -A OUTPUT -m bpf --bytecode "`nfbpf_compile RAW 'ip proto
6'`" -j ACCEPT
Or use tcpdump -ddd. In that case, generate BPF targeting a device
with the same data link type as the xtables match. Iptables passes packets
from the network layer up, without mac layer. Select a device with data link
type RAW, such as a tun device:
- ip tuntap add tun0 mode tun
ip link set tun0 up
tcpdump -ddd -i tun0 ip proto 6
See tcpdump -L -i $dev for a list of known data link types for a
given device.
You may want to learn more about BPF from FreeBSD's bpf(4)
manpage.
- [!] --path path
- Match cgroup2 membership.
Each socket is associated with the v2 cgroup of the creating
process. This matches packets coming from or going to all sockets in the
sub-hierarchy of the specified path. The path should be relative to the
root of the cgroup2 hierarchy.
- [!] --cgroup classid
- Match cgroup net_cls classid.
classid is the marker set through the cgroup net_cls
controller. This option and --path can't be used together.
Example:
- iptables -A OUTPUT -p tcp --sport 80 -m cgroup ! --path
service/http-server -j DROP
- iptables -A OUTPUT -p tcp --sport 80 -m cgroup ! --cgroup 1 -j DROP
IMPORTANT: when being used in the INPUT chain, the cgroup
matcher is currently only of limited functionality, meaning it will only
match on packets that are processed for local sockets through early socket
demuxing. Therefore, general usage on the INPUT chain is not advised unless
the implications are well understood.
Available since Linux 3.14.
Allows you to deploy gateway and back-end load-sharing clusters without the need
of load-balancers.
This match requires that all the nodes see the same packets. Thus,
the cluster match decides if this node has to handle a packet given the
following options:
- --cluster-total-nodes num
- Set number of total nodes in cluster.
- [!] --cluster-local-node num
- Set the local node number ID.
- [!] --cluster-local-nodemask mask
- Set the local node number ID mask. You can use this option instead of
--cluster-local-node.
- --cluster-hash-seed value
- Set seed value of the Jenkins hash.
Example:
- iptables -A PREROUTING -t mangle -i eth1 -m cluster --cluster-total-nodes
2 --cluster-local-node 1 --cluster-hash-seed 0xdeadbeef -j MARK --set-mark
0xffff
- iptables -A PREROUTING -t mangle -i eth2 -m cluster --cluster-total-nodes
2 --cluster-local-node 1 --cluster-hash-seed 0xdeadbeef -j MARK --set-mark
0xffff
- iptables -A PREROUTING -t mangle -i eth1 -m mark ! --mark 0xffff -j
DROP
- iptables -A PREROUTING -t mangle -i eth2 -m mark ! --mark 0xffff -j
DROP
And the following commands to make all nodes see the same
packets:
- ip maddr add 01:00:5e:00:01:01 dev eth1
- ip maddr add 01:00:5e:00:01:02 dev eth2
- arptables -A OUTPUT -o eth1 --h-length 6 -j mangle --mangle-mac-s
01:00:5e:00:01:01
- arptables -A INPUT -i eth1 --h-length 6 --destination-mac
01:00:5e:00:01:01 -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27
- arptables -A OUTPUT -o eth2 --h-length 6 -j mangle --mangle-mac-s
01:00:5e:00:01:02
- arptables -A INPUT -i eth2 --h-length 6 --destination-mac
01:00:5e:00:01:02 -j mangle --mangle-mac-d 00:zz:yy:xx:5a:27
NOTE: the arptables commands above use mainstream syntax.
If you are using arptables-jf included in some RedHat, CentOS and Fedora
versions, you will hit syntax errors. Therefore, you'll have to adapt these
to the arptables-jf syntax to get them working.
In the case of TCP connections, pickup facility has to be disabled
to avoid marking TCP ACK packets coming in the reply direction as valid.
- echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose
Allows you to add comments (up to 256 characters) to any rule.
- --comment comment
- Example:
- iptables -A INPUT -i eth1 -m comment --comment "my local
LAN"
Match by how many bytes or packets a connection (or one of the two flows
constituting the connection) has transferred so far, or by average bytes per
packet.
The counters are 64-bit and are thus not expected to overflow
;)
The primary use is to detect long-lived downloads and mark them to
be scheduled using a lower priority band in traffic control.
The transferred bytes per connection can also be viewed through
`conntrack -L` and accessed via ctnetlink.
NOTE that for connections which have no accounting information,
the match will always return false. The
"net.netfilter.nf_conntrack_acct" sysctl flag controls whether
new connections will be byte/packet counted. Existing connection
flows will not be gaining/losing a/the accounting structure when be sysctl
flag is flipped.
- [!] --connbytes from[:to]
- match packets from a connection whose packets/bytes/average packet size is
more than FROM and less than TO bytes/packets. if TO is omitted only FROM
check is done. "!" is used to match packets not falling in the
range.
- --connbytes-dir {original|reply|both}
- which packets to consider
- --connbytes-mode {packets|bytes|avgpkt}
- whether to check the amount of packets, number of bytes transferred or the
average size (in bytes) of all packets received so far. Note that when
"both" is used together with "avgpkt", and data is
going (mainly) only in one direction (for example HTTP), the average
packet size will be about half of the actual data packets.
- Example:
- iptables .. -m connbytes --connbytes 10000:100000 --connbytes-dir both
--connbytes-mode bytes ...
Allows you to restrict the number of parallel connections to a server per client
IP address (or client address block).
- --connlimit-upto n
- Match if the number of existing connections is below or equal
n.
- --connlimit-above n
- Match if the number of existing connections is above n.
- --connlimit-mask prefix_length
- Group hosts using the prefix length. For IPv4, this must be a number
between (including) 0 and 32. For IPv6, between 0 and 128. If not
specified, the maximum prefix length for the applicable protocol is
used.
- --connlimit-saddr
- Apply the limit onto the source group. This is the default if
--connlimit-daddr is not specified.
- --connlimit-daddr
- Apply the limit onto the destination group.
Examples:
- # allow 2 telnet connections per client host
- iptables -A INPUT -p tcp --syn --dport 23 -m connlimit --connlimit-above 2
-j REJECT
- # you can also match the other way around:
- iptables -A INPUT -p tcp --syn --dport 23 -m connlimit --connlimit-upto 2
-j ACCEPT
- # limit the number of parallel HTTP requests to 16 per class C sized
source network (24 bit netmask)
- iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above 16
--connlimit-mask 24 -j REJECT
- # limit the number of parallel HTTP requests to 16 for the link local
network
- (ipv6) ip6tables -p tcp --syn --dport 80 -s fe80::/64 -m connlimit
--connlimit-above 16 --connlimit-mask 64 -j REJECT
- # Limit the number of connections to a particular host:
- ip6tables -p tcp --syn --dport 49152:65535 -d 2001:db8::1 -m connlimit
--connlimit-above 100 -j REJECT
This module matches the netfilter mark field associated with a connection (which
can be set using the CONNMARK target below).
- [!] --mark value[/mask]
- Matches packets in connections with the given mark value (if a mask is
specified, this is logically ANDed with the mark before the
comparison).
This module, when combined with connection tracking, allows access to the
connection tracking state for this packet/connection.
- [!] --ctstate statelist
- statelist is a comma separated list of the connection states to
match. Possible states are listed below.
- [!] --ctproto l4proto
- Layer-4 protocol to match (by number or name)
- [!] --ctorigsrc address[/mask]
- [!] --ctorigdst address[/mask]
- [!] --ctreplsrc address[/mask]
- [!] --ctrepldst address[/mask]
- Match against original/reply source/destination address
- [!] --ctorigsrcport port[:port]
- [!] --ctorigdstport port[:port]
- [!] --ctreplsrcport port[:port]
- [!] --ctrepldstport port[:port]
- Match against original/reply source/destination port (TCP/UDP/etc.) or GRE
key. Matching against port ranges is only supported in kernel versions
above 2.6.38.
- [!] --ctstatus statelist
- statuslist is a comma separated list of the connection statuses to
match. Possible statuses are listed below.
- [!] --ctexpire time[:time]
- Match remaining lifetime in seconds against given value or range of values
(inclusive)
- --ctdir {ORIGINAL|REPLY}
- Match packets that are flowing in the specified direction. If this flag is
not specified at all, matches packets in both directions.
States for --ctstate:
- INVALID
- The packet is associated with no known connection.
- NEW
- The packet has started a new connection or otherwise associated with a
connection which has not seen packets in both directions.
- ESTABLISHED
- The packet is associated with a connection which has seen packets in both
directions.
- RELATED
- The packet is starting a new connection, but is associated with an
existing connection, such as an FTP data transfer or an ICMP error.
- UNTRACKED
- The packet is not tracked at all, which happens if you explicitly untrack
it by using -j CT --notrack in the raw table.
- SNAT
- A virtual state, matching if the original source address differs from the
reply destination.
- DNAT
- A virtual state, matching if the original destination differs from the
reply source.
Statuses for --ctstatus:
- NONE
- None of the below.
- EXPECTED
- This is an expected connection (i.e. a conntrack helper set it up).
- SEEN_REPLY
- Conntrack has seen packets in both directions.
- ASSURED
- Conntrack entry should never be early-expired.
- CONFIRMED
- Connection is confirmed: originating packet has left box.
- [!] --cpu number
- Match cpu handling this packet. cpus are numbered from 0 to NR_CPUS-1 Can
be used in combination with RPS (Remote Packet Steering) or multiqueue
NICs to spread network traffic on different queues.
Example:
iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 0 -j
REDIRECT --to-port 8080
iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 1 -j
REDIRECT --to-port 8081
Available since Linux 2.6.36.
- [!] --source-port,--sport
port[:port]
- [!] --destination-port,--dport
port[:port]
- [!] --dccp-types mask
- Match when the DCCP packet type is one of 'mask'. 'mask' is a
comma-separated list of packet types. Packet types are: REQUEST
RESPONSE DATA ACK DATAACK CLOSEREQ CLOSE RESET SYNC SYNCACK
INVALID.
- [!] --dccp-option number
- Match if DCCP option set.
Match device group of a packets incoming/outgoing interface.
- [!] --src-group name
- Match device group of incoming device
- [!] --dst-group name
- Match device group of outgoing device
This module matches the 6 bit DSCP field within the TOS field in the IP header.
DSCP has superseded TOS within the IETF.
- [!] --dscp value
- Match against a numeric (decimal or hex) value [0-63].
- [!] --dscp-class class
- Match the DiffServ class. This value may be any of the BE, EF, AFxx or CSx
classes. It will then be converted into its according numeric value.
This module matches the parameters in Destination Options header
- [!] --dst-len length
- Total length of this header in octets.
- --dst-opts
type[:length][,type[:length]...]
- numeric type of option and the length of the option data in octets.
This allows you to match the ECN bits of the IPv4/IPv6 and TCP header. ECN is
the Explicit Congestion Notification mechanism as specified in RFC3168
- [!] --ecn-tcp-cwr
- This matches if the TCP ECN CWR (Congestion Window Received) bit is
set.
- [!] --ecn-tcp-ece
- This matches if the TCP ECN ECE (ECN Echo) bit is set.
- [!] --ecn-ip-ect num
- This matches a particular IPv4/IPv6 ECT (ECN-Capable Transport). You have
to specify a number between `0' and `3'.
This module matches the SPIs in ESP header of IPsec packets.
- [!] --espspi spi[:spi]
This module matches the EUI-64 part of a stateless autoconfigured IPv6 address.
It compares the EUI-64 derived from the source MAC address in Ethernet frame
with the lower 64 bits of the IPv6 source address. But
"Universal/Local" bit is not compared. This module doesn't match
other link layer frame, and is only valid in the PREROUTING,
INPUT and FORWARD chains.
This module matches the parameters in Fragment header.
- [!] --fragid id[:id]
- Matches the given Identification or range of it.
- [!] --fraglen length
- This option cannot be used with kernel version 2.6.10 or later. The length
of Fragment header is static and this option doesn't make sense.
- --fragres
- Matches if the reserved fields are filled with zero.
- --fragfirst
- Matches on the first fragment.
- --fragmore
- Matches if there are more fragments.
- --fraglast
- Matches if this is the last fragment.
hashlimit uses hash buckets to express a rate limiting match (like the
limit match) for a group of connections using a single iptables
rule. Grouping can be done per-hostgroup (source and/or destination address)
and/or per-port. It gives you the ability to express "N packets
per time quantum per group" or "N bytes per seconds"
(see below for some examples).
A hash limit option (--hashlimit-upto,
--hashlimit-above) and --hashlimit-name are required.
- --hashlimit-upto
amount[/second|/minute|/hour|/day]
- Match if the rate is below or equal to amount/quantum. It is
specified either as a number, with an optional time quantum suffix (the
default is 3/hour), or as amountb/second (number of bytes per
second).
- --hashlimit-above
amount[/second|/minute|/hour|/day]
- Match if the rate is above amount/quantum.
- --hashlimit-burst amount
- Maximum initial number of packets to match: this number gets recharged by
one every time the limit specified above is not reached, up to this
number; the default is 5. When byte-based rate matching is requested, this
option specifies the amount of bytes that can exceed the given rate. This
option should be used with caution -- if the entry expires, the burst
value is reset too.
- --hashlimit-mode
{srcip|srcport|dstip|dstport},...
- A comma-separated list of objects to take into consideration. If no
--hashlimit-mode option is given, hashlimit acts like limit, but at the
expensive of doing the hash housekeeping.
- --hashlimit-srcmask prefix
- When --hashlimit-mode srcip is used, all source addresses encountered will
be grouped according to the given prefix length and the so-created subnet
will be subject to hashlimit. prefix must be between (inclusive) 0
and 32. Note that --hashlimit-srcmask 0 is basically doing the same thing
as not specifying srcip for --hashlimit-mode, but is technically more
expensive.
- --hashlimit-dstmask prefix
- Like --hashlimit-srcmask, but for destination addresses.
- --hashlimit-name foo
- The name for the /proc/net/ipt_hashlimit/foo entry.
- --hashlimit-htable-size buckets
- The number of buckets of the hash table
- --hashlimit-htable-max entries
- Maximum entries in the hash.
- --hashlimit-htable-expire msec
- After how many milliseconds do hash entries expire.
- --hashlimit-htable-gcinterval msec
- How many milliseconds between garbage collection intervals.
- --hashlimit-rate-match
- Classify the flow instead of rate-limiting it. This acts like a true/false
match on whether the rate is above/below a certain number
- --hashlimit-rate-interval sec
- Can be used with --hashlimit-rate-match to specify the interval at which
the rate should be sampled
Examples:
- matching on source host
- "1000 packets per second for every host in <IP_ADDRESS>/16" =>
-s <IP_ADDRESS>/16 --hashlimit-mode srcip --hashlimit-upto 1000/sec
- matching on source port
- "100 packets per second for every service of <IP_ADDRESS>" =>
-s <IP_ADDRESS> --hashlimit-mode srcport --hashlimit-upto 100/sec
- matching on subnet
- "10000 packets per minute for every /28 subnet (groups of 8
addresses) in <IP_ADDRESS>/8" => -s <IP_ADDRESS>/8 --hashlimit-mask 28
--hashlimit-upto 10000/min
- matching bytes per second
- "flows exceeding 512kbyte/s" => --hashlimit-mode
srcip,dstip,srcport,dstport --hashlimit-above 512kb/s
- matching bytes per second
- "hosts that exceed 512kbyte/s, but permit up to 1Megabytes without
matching" --hashlimit-mode dstip --hashlimit-above 512kb/s
--hashlimit-burst 1mb
This module matches the parameters in Hop-by-Hop Options header
- [!] --hbh-len length
- Total length of this header in octets.
- --hbh-opts
type[:length][,type[:length]...]
- numeric type of option and the length of the option data in octets.
This module matches packets related to a specific conntrack-helper.
- [!] --helper string
- Matches packets related to the specified conntrack-helper.
string can be "ftp" for packets related to a ftp-session
on default port. For other ports append -portnr to the value, ie.
"ftp-2121".
Same rules apply for other conntrack-helpers.
This module matches the Hop Limit field in the IPv6 header.
- [!] --hl-eq value
- Matches if Hop Limit equals value.
- --hl-lt value
- Matches if Hop Limit is less than value.
- --hl-gt value
- Matches if Hop Limit is greater than value.
This extension can be used if `--protocol icmp' is specified. It provides the
following option:
- [!] --icmp-type
{type[/code]|typename}
- This allows specification of the ICMP type, which can be a numeric ICMP
type, type/code pair, or one of the ICMP type names shown by the command
iptables -p icmp -h
This extension can be used if `--protocol ipv6-icmp' or `--protocol icmpv6' is
specified. It provides the following option:
- [!] --icmpv6-type
type[/code]|typename
- This allows specification of the ICMPv6 type, which can be a numeric
ICMPv6 type, type and code, or one of the ICMPv6 type
names shown by the command
ip6tables -p ipv6-icmp -h
This matches on a given arbitrary range of IP addresses.
- [!] --src-range from[-to]
- Match source IP in the specified range.
- [!] --dst-range from[-to]
- Match destination IP in the specified range.
This module matches IPv6 extension headers and/or upper layer header.
- --soft
- Matches if the packet includes any of the headers specified with
--header.
- [!] --header header[,header...]
- Matches the packet which EXACTLY includes all specified headers. The
headers encapsulated with ESP header are out of scope. Possible
header types can be:
- hop|hop-by-hop
- Hop-by-Hop Options header
- dst
- Destination Options header
- route
- Routing header
- frag
- Fragment header
- auth
- Authentication header
- esp
- Encapsulating Security Payload header
- none
- No Next header which matches 59 in the 'Next Header field' of IPv6 header
or any IPv6 extension headers
- prot
- which matches any upper layer protocol header. A protocol name from
/etc/protocols and numeric value also allowed. The number 255 is
equivalent to prot.
Match IPVS connection properties.
- [!] --ipvs
- packet belongs to an IPVS connection
- Any of the following options implies --ipvs (even negated)
- [!] --vproto protocol
- VIP protocol to match; by number or name, e.g. "tcp"
- [!] --vaddr address[/mask]
- VIP address to match
- [!] --vport port
- VIP port to match; by number or name, e.g. "http"
- --vdir {ORIGINAL|REPLY}
- flow direction of packet
- [!] --vmethod {GATE|IPIP|MASQ}
- IPVS forwarding method used
- [!] --vportctl port
- VIP port of the controlling connection to match, e.g. 21 for FTP
This module matches the length of the layer-3 payload (e.g. layer-4 packet) of a
packet against a specific value or range of values.
- [!] --length length[:length]
This module matches at a limited rate using a token bucket filter. A rule using
this extension will match until this limit is reached. It can be used in
combination with the LOG target to give limited logging, for example.
xt_limit has no negation support - you will have to use -m
hashlimit ! --hashlimit rate in this case whilst omitting
--hashlimit-mode.
- --limit
rate[/second|/minute|/hour|/day]
- Maximum average matching rate: specified as a number, with an optional
`/second', `/minute', `/hour', or `/day' suffix; the default is
3/hour.
- --limit-burst number
- Maximum initial number of packets to match: this number gets recharged by
one every time the limit specified above is not reached, up to this
number; the default is 5.
- [!] --mac-source address
- Match source MAC address. It must be of the form XX:XX:XX:XX:XX:XX. Note
that this only makes sense for packets coming from an Ethernet device and
entering the PREROUTING, FORWARD or INPUT
chains.
This module matches the netfilter mark field associated with a packet (which can
be set using the MARK target below).
- [!] --mark value[/mask]
- Matches packets with the given unsigned mark value (if a mask is
specified, this is logically ANDed with the mask before the
comparison).
This extension is loaded if `--protocol ipv6-mh' or `--protocol mh' is
specified. It provides the following option:
- [!] --mh-type type[:type]
- This allows specification of the Mobility Header(MH) type, which can be a
numeric MH type, type or one of the MH type names shown by
the command
ip6tables -p mh -h
This module matches a set of source or destination ports. Up to 15 ports can be
specified. A port range (port:port) counts as two ports. It can only be used
in conjunction with one of the following protocols: tcp, udp,
udplite, dccp and sctp.
- [!] --source-ports,--sports
port[,port|,port:port]...
- Match if the source port is one of the given ports. The flag
--sports is a convenient alias for this option. Multiple ports or
port ranges are separated using a comma, and a port range is specified
using a colon. 53,1024:65535 would therefore match ports 53 and all
from 1024 through 65535.
- [!] --destination-ports,--dports
port[,port|,port:port]...
- Match if the destination port is one of the given ports. The flag
--dports is a convenient alias for this option.
- [!] --ports
port[,port|,port:port]...
- Match if either the source or destination ports are equal to one of the
given ports.
The nfacct match provides the extended accounting infrastructure for iptables.
You have to use this match together with the standalone user-space utility
nfacct(8)
The only option available for this match is the following:
- --nfacct-name name
- This allows you to specify the existing object name that will be use for
accounting the traffic that this rule-set is matching.
To use this extension, you have to create an accounting
object:
- nfacct add http-traffic
Then, you have to attach it to the accounting object via
iptables:
- iptables -I INPUT -p tcp --sport 80 -m nfacct --nfacct-name
http-traffic
- iptables -I OUTPUT -p tcp --dport 80 -m nfacct --nfacct-name
http-traffic
Then, you can check for the amount of traffic that the rules
match:
- nfacct get http-traffic
- { pkts =<PHONE_NUMBER>0000000156, bytes =<PHONE_NUMBER>0000151786 } =
http-traffic;
You can obtain nfacct(8) from http://www.netfilter.org or,
alternatively, from the git.netfilter.org repository.
The osf module does passive operating system fingerprinting. This modules
compares some data (Window Size, MSS, options and their order, TTL, DF, and
others) from packets with the SYN bit set.
- [!] --genre string
- Match an operating system genre by using a passive fingerprinting.
- --ttl level
- Do additional TTL checks on the packet to determine the operating system.
level can be one of the following values:
- 0 - True IP address and fingerprint TTL comparison. This generally works
for LANs.
- 1 - Check if the IP header's TTL is less than the fingerprint one. Works
for globally-routable addresses.
- 2 - Do not compare the TTL at all.
- --log level
- Log determined genres into dmesg even if they do not match the desired
one. level can be one of the following values:
- 0 - Log all matched or unknown signatures
- 1 - Log only the first one
- 2 - Log all known matched signatures
You may find something like this in syslog:
Windows [2000:SP3:Windows XP Pro SP1, 2000 SP3]: <IP_ADDRESS>:4024
-> <IP_ADDRESS>:139 hops=3 Linux [2.5-2.6:] : <IP_ADDRESS>:42624 ->
<IP_ADDRESS>:22 hops=4
OS fingerprints are loadable using the nfnl_osf program. To
load fingerprints from a file, use:
nfnl_osf -f /usr/share/xtables/pf.os
To remove them again,
nfnl_osf -f /usr/share/xtables/pf.os -d
The fingerprint database can be downloaded from
http://www.openbsd.org/cgi-bin/cvsweb/src/etc/pf.os .
This module attempts to match various characteristics of the packet creator, for
locally generated packets. This match is only valid in the OUTPUT and
POSTROUTING chains. Forwarded packets do not have any socket associated with
them. Packets from kernel threads do have a socket, but usually no owner.
- [!] --uid-owner username
- [!] --uid-owner userid[-userid]
- Matches if the packet socket's file structure (if it has one) is owned by
the given user. You may also specify a numerical UID, or an UID
range.
- [!] --gid-owner groupname
- [!] --gid-owner groupid[-groupid]
- Matches if the packet socket's file structure is owned by the given group.
You may also specify a numerical GID, or a GID range.
- --suppl-groups
- Causes group(s) specified with --gid-owner to be also checked in
the supplementary groups of a process.
- [!] --socket-exists
- Matches if the packet is associated with a socket.
This module matches on the bridge port input and output devices enslaved to a
bridge device. This module is a part of the infrastructure that enables a
transparent bridging IP firewall and is only useful for kernel versions above
version 2.5.44.
- [!] --physdev-in name
- Name of a bridge port via which a packet is received (only for packets
entering the INPUT, FORWARD and PREROUTING chains).
If the interface name ends in a "+", then any interface which
begins with this name will match. If the packet didn't arrive through a
bridge device, this packet won't match this option, unless '!' is
used.
- [!] --physdev-out name
- Name of a bridge port via which a packet is going to be sent (for bridged
packets entering the FORWARD and POSTROUTING chains). If the
interface name ends in a "+", then any interface which begins
with this name will match.
- [!] --physdev-is-in
- Matches if the packet has entered through a bridge interface.
- [!] --physdev-is-out
- Matches if the packet will leave through a bridge interface.
- [!] --physdev-is-bridged
- Matches if the packet is being bridged and therefore is not being routed.
This is only useful in the FORWARD and POSTROUTING chains.
This module matches the link-layer packet type.
- [!] --pkt-type
{unicast|broadcast|multicast}
This modules matches the policy used by IPsec for handling a packet.
- --dir {in|out}
- Used to select whether to match the policy used for decapsulation or the
policy that will be used for encapsulation. in is valid in the
PREROUTING, INPUT and FORWARD chains, out is valid in the
POSTROUTING, OUTPUT and FORWARD chains.
- --pol {none|ipsec}
- Matches if the packet is subject to IPsec processing. --pol none
cannot be combined with --strict.
- --strict
- Selects whether to match the exact policy or match if any rule of the
policy matches the given policy.
For each policy element that is to be described, one can use one
or more of the following options. When --strict is in effect, at
least one must be used per element.
- [!] --reqid id
- Matches the reqid of the policy rule. The reqid can be specified with
setkey(8) using unique:id as level.
- [!] --spi spi
- Matches the SPI of the SA.
- [!] --proto {ah|esp|ipcomp}
- Matches the encapsulation protocol.
- [!] --mode {tunnel|transport}
- Matches the encapsulation mode.
- [!] --tunnel-src addr[/mask]
- Matches the source end-point address of a tunnel mode SA. Only valid with
--mode tunnel.
- [!] --tunnel-dst addr[/mask]
- Matches the destination end-point address of a tunnel mode SA. Only valid
with --mode tunnel.
- --next
- Start the next element in the policy specification. Can only be used with
--strict.
Implements network quotas by decrementing a byte counter with each packet. The
condition matches until the byte counter reaches zero. Behavior is reversed
with negation (i.e. the condition does not match until the byte counter
reaches zero).
- [!] --quota bytes
- The quota in bytes.
The rate estimator can match on estimated rates as collected by the RATEEST
target. It supports matching on absolute bps/pps values, comparing two rate
estimators and matching on the difference between two rate estimators.
For a better understanding of the available options, these are all
possible combinations:
- rateest operator rateest-bps
- rateest operator rateest-pps
- (rateest minus rateest-bps1) operator
rateest-bps2
- (rateest minus rateest-pps1) operator
rateest-pps2
- rateest1 operator rateest2 rateest-bps(without
rate!)
- rateest1 operator rateest2 rateest-pps(without
rate!)
- (rateest1 minus rateest-bps1) operator
(rateest2 minus rateest-bps2)
- (rateest1 minus rateest-pps1) operator
(rateest2 minus rateest-pps2)
- --rateest-delta
- For each estimator (either absolute or relative mode), calculate the
difference between the estimator-determined flow rate and the static value
chosen with the BPS/PPS options. If the flow rate is higher than the
specified BPS/PPS, 0 will be used instead of a negative value. In other
words, "max(0, rateest#_rate - rateest#_bps)" is used.
- [!] --rateest-lt
- Match if rate is less than given rate/estimator.
- [!] --rateest-gt
- Match if rate is greater than given rate/estimator.
- [!] --rateest-eq
- Match if rate is equal to given rate/estimator.
In the so-called "absolute mode", only one rate
estimator is used and compared against a static value, while in
"relative mode", two rate estimators are compared against
another.
- --rateest name
- Name of the one rate estimator for absolute mode.
- --rateest1 name
- --rateest2 name
- The names of the two rate estimators for relative mode.
- --rateest-bps [value]
- --rateest-pps [value]
- --rateest-bps1 [value]
- --rateest-bps2 [value]
- --rateest-pps1 [value]
- --rateest-pps2 [value]
- Compare the estimator(s) by bytes or packets per second, and compare
against the chosen value. See the above bullet list for which option is to
be used in which case. A unit suffix may be used - available ones are:
bit, [kmgt]bit, [KMGT]ibit, Bps, [KMGT]Bps, [KMGT]iBps.
Example: This is what can be used to route outgoing data
connections from an FTP server over two lines based on the available
bandwidth at the time the data connection was started:
# Estimate outgoing rates
iptables -t mangle -A POSTROUTING -o eth0 -j RATEEST
--rateest-name eth0 --rateest-interval 250ms --rateest-ewma 0.5s
iptables -t mangle -A POSTROUTING -o ppp0 -j RATEEST
--rateest-name ppp0 --rateest-interval 250ms --rateest-ewma 0.5s
# Mark based on available bandwidth
iptables -t mangle -A balance -m conntrack --ctstate NEW -m helper
--helper ftp -m rateest --rateest-delta --rateest1 eth0 --rateest-bps1
2.5mbit --rateest-gt --rateest2 ppp0 --rateest-bps2 2mbit -j CONNMARK
--set-mark 1
iptables -t mangle -A balance -m conntrack --ctstate NEW -m helper
--helper ftp -m rateest --rateest-delta --rateest1 ppp0 --rateest-bps1 2mbit
--rateest-gt --rateest2 eth0 --rateest-bps2 2.5mbit -j CONNMARK --set-mark
2
iptables -t mangle -A balance -j CONNMARK --restore-mark
This matches the routing realm. Routing realms are used in complex routing
setups involving dynamic routing protocols like BGP.
- [!] --realm value[/mask]
- Matches a given realm number (and optionally mask). If not a number, value
can be a named realm from /etc/iproute2/rt_realms (mask can not be used in
that case). Both value and mask are four byte unsigned integers and may be
specified in decimal, hex (by prefixing with "0x") or octal (if
a leading zero is given).
Allows you to dynamically create a list of IP addresses and then match against
that list in a few different ways.
For example, you can create a "badguy" list out of
people attempting to connect to port 139 on your firewall and then DROP all
future packets from them without considering them.
--set, --rcheck, --update and --remove
are mutually exclusive.
- --name name
- Specify the list to use for the commands. If no name is given then
DEFAULT will be used.
- [!] --set
- This will add the source address of the packet to the list. If the source
address is already in the list, this will update the existing entry. This
will always return success (or failure if ! is passed in).
- --rsource
- Match/save the source address of each packet in the recent list table.
This is the default.
- --rdest
- Match/save the destination address of each packet in the recent list
table.
- --mask netmask
- Netmask that will be applied to this recent list.
- [!] --rcheck
- Check if the source address of the packet is currently in the list.
- [!] --update
- Like --rcheck, except it will update the "last seen"
timestamp if it matches.
- [!] --remove
- Check if the source address of the packet is currently in the list and if
so that address will be removed from the list and the rule will return
true. If the address is not found, false is returned.
- --seconds seconds
- This option must be used in conjunction with one of --rcheck or
--update. When used, this will narrow the match to only happen when
the address is in the list and was seen within the last given number of
seconds.
- --reap
- This option can only be used in conjunction with --seconds. When
used, this will cause entries older than the last given number of seconds
to be purged.
- --hitcount hits
- This option must be used in conjunction with one of --rcheck or
--update. When used, this will narrow the match to only happen when
the address is in the list and packets had been received greater than or
equal to the given value. This option may be used along with
--seconds to create an even narrower match requiring a certain
number of hits within a specific time frame. The maximum value for the
hitcount parameter is given by the "ip_pkt_list_tot" parameter
of the xt_recent kernel module. Exceeding this value on the command line
will cause the rule to be rejected.
- --rttl
- This option may only be used in conjunction with one of --rcheck or
--update. When used, this will narrow the match to only happen when
the address is in the list and the TTL of the current packet matches that
of the packet which hit the --set rule. This may be useful if you
have problems with people faking their source address in order to DoS you
via this module by disallowing others access to your site by sending bogus
packets to you.
Examples:
- iptables -A FORWARD -m recent --name badguy --rcheck --seconds 60 -j
DROP
- iptables -A FORWARD -p tcp -i eth0 --dport 139 -m recent --name badguy
--set -j DROP
/proc/net/xt_recent/* are the current lists of addresses
and information about each entry of each list.
Each file in /proc/net/xt_recent/ can be read from to see
the current list or written two using the following commands to modify the
list:
- echo +addr >/proc/net/xt_recent/DEFAULT
- to add addr to the DEFAULT list
- echo -addr >/proc/net/xt_recent/DEFAULT
- to remove addr from the DEFAULT list
- echo / >/proc/net/xt_recent/DEFAULT
- to flush the DEFAULT list (remove all entries).
The module itself accepts parameters, defaults shown:
- ip_list_tot=100
- Number of addresses remembered per table.
- ip_pkt_list_tot=20
- Number of packets per address remembered.
- ip_list_hash_size=0
- Hash table size. 0 means to calculate it based on ip_list_tot, default:
512.
- ip_list_perms=0644
- Permissions for /proc/net/xt_recent/* files.
- ip_list_uid=0
- Numerical UID for ownership of /proc/net/xt_recent/* files.
- ip_list_gid=0
- Numerical GID for ownership of /proc/net/xt_recent/* files.
Performs a reverse path filter test on a packet. If a reply to the packet would
be sent via the same interface that the packet arrived on, the packet will
match. Note that, unlike the in-kernel rp_filter, packets protected by IPSec
are not treated specially. Combine this match with the policy match if you
want this. Also, packets arriving via the loopback interface are always
permitted. This match can only be used in the PREROUTING chain of the raw or
mangle table.
- --loose
- Used to specify that the reverse path filter test should match even if the
selected output device is not the expected one.
- --validmark
- Also use the packets' nfmark value when performing the reverse path route
lookup.
- --accept-local
- This will permit packets arriving from the network with a source address
that is also assigned to the local machine.
- --invert
- This will invert the sense of the match. Instead of matching packets that
passed the reverse path filter test, match those that have failed it.
Example to log and drop packets failing the reverse path filter
test:
iptables -t raw -N RPFILTER
iptables -t raw -A RPFILTER -m rpfilter -j RETURN
iptables -t raw -A RPFILTER -m limit --limit 10/minute -j NFLOG
--nflog-prefix "rpfilter drop"
iptables -t raw -A RPFILTER -j DROP
iptables -t raw -A PREROUTING -j RPFILTER
Example to drop failed packets, without logging:
iptables -t raw -A RPFILTER -m rpfilter --invert -j DROP
Match on IPv6 routing header
- [!] --rt-type type
- Match the type (numeric).
- [!] --rt-segsleft num[:num]
- Match the `segments left' field (range).
- [!] --rt-len length
- Match the length of this header.
- --rt-0-res
- Match the reserved field, too (type=0)
- --rt-0-addrs addr[,addr...]
- Match type=0 addresses (list).
- --rt-0-not-strict
- List of type=0 addresses is not a strict list.
- [!] --source-port,--sport
port[:port]
- [!] --destination-port,--dport
port[:port]
- [!] --chunk-types {all|any|only}
chunktype[:flags] [...]
- The flag letter in upper case indicates that the flag is to match if set,
in the lower case indicates to match if unset.
Chunk types: DATA INIT INIT_ACK SACK HEARTBEAT HEARTBEAT_ACK
ABORT SHUTDOWN SHUTDOWN_ACK ERROR COOKIE_ECHO COOKIE_ACK ECN_ECNE
ECN_CWR SHUTDOWN_COMPLETE ASCONF ASCONF_ACK FORWARD_TSN
chunk type available flags
DATA I U B E i u b e
ABORT T t
SHUTDOWN_COMPLETE T t
(lowercase means flag should be "off", uppercase
means "on")
Examples:
iptables -A INPUT -p sctp --dport 80 -j DROP
iptables -A INPUT -p sctp --chunk-types any DATA,INIT -j DROP
iptables -A INPUT -p sctp --chunk-types any DATA:Be -j ACCEPT
This module matches IP sets which can be defined by ipset(8).
- [!] --match-set setname
flag[,flag]...
- where flags are the comma separated list of src and/or dst
specifications and there can be no more than six of them. Hence the
command
-
iptables -A FORWARD -m set --match-set test src,dst
- will match packets, for which (if the set type is ipportmap) the source
address and destination port pair can be found in the specified set. If
the set type of the specified set is single dimension (for example ipmap),
then the command will match packets for which the source address can be
found in the specified set.
- --return-nomatch
- If the --return-nomatch option is specified and the set type
supports the nomatch flag, then the matching is reversed: a match
with an element flagged with nomatch returns true, while a
match with a plain element returns false.
- ! --update-counters
- If the --update-counters flag is negated, then the packet and byte
counters of the matching element in the set won't be updated. Default the
packet and byte counters are updated.
- ! --update-subcounters
- If the --update-subcounters flag is negated, then the packet and
byte counters of the matching element in the member set of a list type of
set won't be updated. Default the packet and byte counters are
updated.
- [!] --packets-eq value
- If the packet is matched an element in the set, match only if the packet
counter of the element matches the given value too.
- --packets-lt value
- If the packet is matched an element in the set, match only if the packet
counter of the element is less than the given value as well.
- --packets-gt value
- If the packet is matched an element in the set, match only if the packet
counter of the element is greater than the given value as well.
- [!] --bytes-eq value
- If the packet is matched an element in the set, match only if the byte
counter of the element matches the given value too.
- --bytes-lt value
- If the packet is matched an element in the set, match only if the byte
counter of the element is less than the given value as well.
- --bytes-gt value
- If the packet is matched an element in the set, match only if the byte
counter of the element is greater than the given value as well.
The packet and byte counters related options and flags are ignored
when the set was defined without counter support.
The option --match-set can be replaced by --set if
that does not clash with an option of other extensions.
Use of -m set requires that ipset kernel support is provided,
which, for standard kernels, is the case since Linux 2.6.39.
This matches if an open TCP/UDP socket can be found by doing a socket lookup on
the packet. It matches if there is an established or non-zero bound listening
socket (possibly with a non-local address). The lookup is performed using the
packet tuple of TCP/UDP packets, or the original TCP/UDP header
embedded in an ICMP/ICPMv6 error packet.
- --transparent
- Ignore non-transparent sockets.
- --nowildcard
- Do not ignore sockets bound to 'any' address. The socket match won't
accept zero-bound listeners by default, since then local services could
intercept traffic that would otherwise be forwarded. This option therefore
has security implications when used to match traffic being forwarded to
redirect such packets to local machine with policy routing. When using the
socket match to implement fully transparent proxies bound to non-local
addresses it is recommended to use the --transparent option instead.
Example (assuming packets with mark 1 are delivered locally):
- -t mangle -A PREROUTING -m socket --transparent -j MARK --set-mark 1
- --restore-skmark
- Set the packet mark to the matching socket's mark. Can be combined with
the --transparent and --nowildcard options to restrict the
sockets to be matched when restoring the packet mark.
Example: An application opens 2 transparent
(IP_TRANSPARENT) sockets and sets a mark on them with SO_MARK
socket option. We can filter matching packets:
- -t mangle -I PREROUTING -m socket --transparent --restore-skmark -j
action
- -t mangle -A action -m mark --mark 10 -j action2
- -t mangle -A action -m mark --mark 11 -j action3
The "state" extension is a subset of the "conntrack" module.
"state" allows access to the connection tracking state for this
packet.
- [!] --state state
- Where state is a comma separated list of the connection states to match.
Only a subset of the states unterstood by "conntrack" are
recognized: INVALID, ESTABLISHED, NEW, RELATED
or UNTRACKED. For their description, see the "conntrack"
heading in this manpage.
This module matches packets based on some statistic condition. It supports two
distinct modes settable with the --mode option.
Supported options:
- --mode mode
- Set the matching mode of the matching rule, supported modes are
random and nth.
- [!] --probability p
- Set the probability for a packet to be randomly matched. It only works
with the random mode. p must be within 0.0 and 1.0. The
supported granularity is in 1/2147483648th increments.
- [!] --every n
- Match one packet every nth packet. It works only with the nth mode
(see also the --packet option).
- --packet p
- Set the initial counter value (0 <= p <= n-1, default 0) for the
nth mode.
This modules matches a given string by using some pattern matching strategy. It
requires a linux kernel >= 2.6.14.
- --algo {bm|kmp}
- Select the pattern matching strategy. (bm = Boyer-Moore, kmp =
Knuth-Pratt-Morris)
- --from offset
- Set the offset from which it starts looking for any matching. If not
passed, default is 0.
- --to offset
- Set the offset up to which should be scanned. That is, byte
offset-1 (counting from 0) is the last one that is scanned. If not
passed, default is the packet size.
- [!] --string pattern
- Matches the given pattern.
- [!] --hex-string pattern
- Matches the given pattern in hex notation.
- --icase
- Ignore case when searching.
- Examples:
- # The string pattern can be used for simple text characters.
iptables -A INPUT -p tcp --dport 80 -m string --algo bm --string 'GET
/index.html' -j LOG
- # The hex string pattern can be used for non-printable characters, like
|0D 0A| or |0D0A|.
iptables -p udp --dport 53 -m string --algo bm --from 40 --to 57
--hex-string '|03|www|09|netfilter|03|org|00|'
These extensions can be used if `--protocol tcp' is specified. It provides the
following options:
- [!] --source-port,--sport
port[:port]
- Source port or port range specification. This can either be a service name
or a port number. An inclusive range can also be specified, using the
format first:last. If the first port is omitted,
"0" is assumed; if the last is omitted, "65535" is
assumed. The flag --sport is a convenient alias for this
option.
- [!] --destination-port,--dport
port[:port]
- Destination port or port range specification. The flag --dport is a
convenient alias for this option.
- [!] --tcp-flags mask comp
- Match when the TCP flags are as specified. The first argument mask
is the flags which we should examine, written as a comma-separated list,
and the second argument comp is a comma-separated list of flags
which must be set. Flags are: SYN ACK FIN RST URG PSH ALL NONE.
Hence the command
iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN
will only match packets with the SYN flag set, and the ACK, FIN and RST
flags unset.
- [!] --syn
- Only match TCP packets with the SYN bit set and the ACK,RST and FIN bits
cleared. Such packets are used to request TCP connection initiation; for
example, blocking such packets coming in an interface will prevent
incoming TCP connections, but outgoing TCP connections will be unaffected.
It is equivalent to --tcp-flags SYN,RST,ACK,FIN SYN. If the
"!" flag precedes the "--syn", the sense of the option
is inverted.
- [!] --tcp-option number
- Match if TCP option set.
This matches the TCP MSS (maximum segment size) field of the TCP header. You can
only use this on TCP SYN or SYN/ACK packets, since the MSS is only negotiated
during the TCP handshake at connection startup time.
- [!] --mss value[:value]
- Match a given TCP MSS value or range. If a range is given, the second
value must be greater than or equal to the first value.
This matches if the packet arrival time/date is within a given range. All
options are optional, but are ANDed when specified. All times are interpreted
as UTC by default.
- --datestart
YYYY[-MM[-DD[Thh[:mm[:ss]]]]]
- --datestop
YYYY[-MM[-DD[Thh[:mm[:ss]]]]]
- Only match during the given time, which must be in ISO 8601 "T"
notation. The possible time range is 1970-01-01T00:00:00 to
2038-01-19T04:17:07.
- If --datestart or --datestop are not specified, it will default to
1970-01-01 and 2038-01-19, respectively.
- --timestart hh:mm[:ss]
- --timestop hh:mm[:ss]
- Only match during the given daytime. The possible time range is 00:00:00
to 23:59:59. Leading zeroes are allowed (e.g. "06:03") and
correctly interpreted as base-10.
- [!] --monthdays day[,day...]
- Only match on the given days of the month. Possible values are 1 to
31. Note that specifying 31 will of course not match on
months which do not have a 31st day; the same goes for 28- or 29-day
February.
- [!] --weekdays day[,day...]
- Only match on the given weekdays. Possible values are Mon,
Tue, Wed, Thu, Fri, Sat, Sun, or
values from 1 to 7, respectively. You may also use
two-character variants (Mo, Tu, etc.).
- --contiguous
- When --timestop is smaller than --timestart value, match
this as a single time period instead distinct intervals. See
EXAMPLES.
- --kerneltz
- Use the kernel timezone instead of UTC to determine whether a packet meets
the time regulations.
About kernel timezones: Linux keeps the system time in UTC, and
always does so. On boot, system time is initialized from a referential time
source. Where this time source has no timezone information, such as the x86
CMOS RTC, UTC will be assumed. If the time source is however not in UTC,
userspace should provide the correct system time and timezone to the kernel
once it has the information.
Local time is a feature on top of the (timezone independent)
system time. Each process has its own idea of local time, specified via the
TZ environment variable. The kernel also has its own timezone offset
variable. The TZ userspace environment variable specifies how the UTC-based
system time is displayed, e.g. when you run date(1), or what you see on your
desktop clock. The TZ string may resolve to different offsets at different
dates, which is what enables the automatic time-jumping in userspace. when
DST changes. The kernel's timezone offset variable is used when it has to
convert between non-UTC sources, such as FAT filesystems, to UTC (since the
latter is what the rest of the system uses).
The caveat with the kernel timezone is that Linux distributions
may ignore to set the kernel timezone, and instead only set the system time.
Even if a particular distribution does set the timezone at boot, it is
usually does not keep the kernel timezone offset - which is what changes on
DST - up to date. ntpd will not touch the kernel timezone, so running it
will not resolve the issue. As such, one may encounter a timezone that is
always +0000, or one that is wrong half of the time of the year. As such,
using --kerneltz is highly discouraged.
EXAMPLES. To match on weekends, use:
- -m time --weekdays Sa,Su
Or, to match (once) on a national holiday block:
- -m time --datestart 2007-12-24 --datestop 2007-12-27
Since the stop time is actually inclusive, you would need the
following stop time to not match the first second of the new day:
- -m time --datestart 2007-01-01T17:00 --datestop 2007-01-01T23:59:59
During lunch hour:
- -m time --timestart 12:30 --timestop 13:30
The fourth Friday in the month:
- -m time --weekdays Fr --monthdays 22,23,24,25,26,27,28
(Note that this exploits a certain mathematical property. It is
not possible to say "fourth Thursday OR fourth Friday" in one
rule. It is possible with multiple rules, though.)
Matching across days might not do what is expected. For
instance,
- -m time --weekdays Mo --timestart 23:00 --timestop 01:00 Will match
Monday, for one hour from midnight to 1 a.m., and then again for another
hour from 23:00 onwards. If this is unwanted, e.g. if you would like
'match for two hours from Montay 23:00 onwards' you need to also specify
the --contiguous option in the example above.
This module matches the 8-bit Type of Service field in the IPv4 header (i.e.
including the "Precedence" bits) or the (also 8-bit) Priority field
in the IPv6 header.
- [!] --tos value[/mask]
- Matches packets with the given TOS mark value. If a mask is specified, it
is logically ANDed with the TOS mark before the comparison.
- [!] --tos symbol
- You can specify a symbolic name when using the tos match for IPv4. The
list of recognized TOS names can be obtained by calling iptables with
-m tos -h. Note that this implies a mask of 0x3F, i.e. all but the
ECN bits.
This module matches the time to live field in the IP header.
- [!] --ttl-eq ttl
- Matches the given TTL value.
- --ttl-gt ttl
- Matches if TTL is greater than the given TTL value.
- --ttl-lt ttl
- Matches if TTL is less than the given TTL value.
U32 tests whether quantities of up to 4 bytes extracted from a packet have
specified values. The specification of what to extract is general enough to
find data at given offsets from tcp headers or payloads.
- [!] --u32 tests
- The argument amounts to a program in a small language described
below.
- tests := location "=" value | tests "&&"
location "=" value
- value := range | value "," range
- range := number | number ":" number
a single number, n, is interpreted the same as n:n.
n:m is interpreted as the range of numbers >=n and
<=m.
-
- location := number | location operator number
-
- operator := "&" | "<<" |
">>" | "@"
The operators &, <<, >> and
&& mean the same as in C. The = is really a set
membership operator and the value syntax describes a set. The @
operator is what allows moving to the next header and is described further
below.
There are currently some artificial implementation limits on the
size of the tests:
- *
- no more than 10 of "=" (and 9
"&&"s) in the u32 argument
- *
- no more than 10 ranges (and 9 commas) per value
- *
- no more than 10 numbers (and 9 operators) per location
To describe the meaning of location, imagine the following machine
that interprets it. There are three registers:
- A is of type char *, initially the address of the IP header
- B and C are unsigned 32 bit integers, initially zero
The instructions are:
- number
- B = number;
- C = (*(A+B)<<24) + (*(A+B+1)<<16) + (*(A+B+2)<<8) +
*(A+B+3)
- &number
- C = C & number
- << number
- C = C << number
- >> number
- C = C >> number
- @number
- A = A + C; then do the instruction number
Any access of memory outside [skb->data,skb->end] causes the
match to fail. Otherwise the result of the computation is the final value of
C.
Whitespace is allowed but not required in the tests. However, the
characters that do occur there are likely to require shell quoting, so it is
a good idea to enclose the arguments in quotes.
Example:
- match IP packets with total length >= 256
- The IP header contains a total length field in bytes 2-3.
- --u32 "0 & 0xFFFF = 0x100:0xFFFF"
- read bytes 0-3
- AND that with 0xFFFF (giving bytes 2-3), and test whether that is in the
range [0x100:0xFFFF]
Example: (more realistic, hence more complicated)
- match ICMP packets with icmp type 0
- First test that it is an ICMP packet, true iff byte 9 (protocol) = 1
- --u32 "6 & 0xFF = 1 && ...
- read bytes 6-9, use & to throw away bytes 6-8 and compare the
result to 1. Next test that it is not a fragment. (If so, it might be part
of such a packet but we cannot always tell.) N.B.: This test is generally
needed if you want to match anything beyond the IP header. The last 6 bits
of byte 6 and all of byte 7 are 0 iff this is a complete packet (not a
fragment). Alternatively, you can allow first fragments by only testing
the last 5 bits of byte 6.
-
... 4 & 0x3FFF = 0 && ...
- Last test: the first byte past the IP header (the type) is 0. This is
where we have to use the @syntax. The length of the IP header (IHL) in 32
bit words is stored in the right half of byte 0 of the IP header
itself.
-
... 0 >> 22 & 0x3C @ 0 >> 24 = 0"
- The first 0 means read bytes 0-3, >>22 means shift that 22
bits to the right. Shifting 24 bits would give the first byte, so only 22
bits is four times that plus a few more bits. &3C then
eliminates the two extra bits on the right and the first four bits of the
first byte. For instance, if IHL=5, then the IP header is 20 (4 x 5) bytes
long. In this case, bytes 0-1 are (in binary) xxxx0101 yyzzzzzz,
>>22 gives the 10 bit value xxxx0101yy and &3C
gives 010100. @ means to use this number as a new offset into the
packet, and read four bytes starting from there. This is the first 4 bytes
of the ICMP payload, of which byte 0 is the ICMP type. Therefore, we
simply shift the value 24 to the right to throw out all but the first byte
and compare the result with 0.
Example:
- TCP payload bytes 8-12 is any of 1, 2, 5 or 8
- First we test that the packet is a tcp packet (similar to ICMP).
- --u32 "6 & 0xFF = 6 && ...
- Next, test that it is not a fragment (same as above).
-
... 0 >> 22 & 0x3C @ 12 >> 26 & 0x3C @ 8 =
1,2,5,8"
- 0>>22&3C as above computes the number of bytes in the IP
header. @ makes this the new offset into the packet, which is the
start of the TCP header. The length of the TCP header (again in 32 bit
words) is the left half of byte 12 of the TCP header. The
12>>26&3C computes this length in bytes (similar to the
IP header before). "@" makes this the new offset, which is the
start of the TCP payload. Finally, 8 reads bytes 8-12 of the payload and
= checks whether the result is any of 1, 2, 5 or 8.
These extensions can be used if `--protocol udp' is specified. It provides the
following options:
- [!] --source-port,--sport
port[:port]
- Source port or port range specification. See the description of the
--source-port option of the TCP extension for details.
- [!] --destination-port,--dport
port[:port]
- Destination port or port range specification. See the description of the
--destination-port option of the TCP extension for details.
iptables can use extended target modules: the following are included in the
standard distribution.
This target allows to create audit records for packets hitting the target. It
can be used to record accepted, dropped, and rejected packets. See auditd(8)
for additional details.
- --type {accept|drop|reject}
- Set type of audit record. Starting with linux-4.12, this option has no
effect on generated audit messages anymore. It is still accepted by
iptables for compatibility reasons, but ignored.
Example:
- iptables -N AUDIT_DROP
- iptables -A AUDIT_DROP -j AUDIT
- iptables -A AUDIT_DROP -j DROP
This target allows to selectively work around broken/old applications. It can
only be used in the mangle table.
- --checksum-fill
- Compute and fill in the checksum in a packet that lacks a checksum. This
is particularly useful, if you need to work around old applications such
as dhcp clients, that do not work well with checksum offloads, but don't
want to disable checksum offload in your device.
This module allows you to set the skb->priority value (and thus classify the
packet into a specific CBQ class).
- --set-class major:minor
- Set the major and minor class value. The values are always interpreted as
hexadecimal even if no 0x prefix is given.
This module allows you to configure a simple cluster of nodes that share a
certain IP and MAC address without an explicit load balancer in front of them.
Connections are statically distributed between the nodes in this cluster.
- --new
- Create a new ClusterIP. You always have to set this on the first rule for
a given ClusterIP.
- --hashmode mode
- Specify the hashing mode. Has to be one of sourceip,
sourceip-sourceport, sourceip-sourceport-destport.
- --clustermac mac
- Specify the ClusterIP MAC address. Has to be a link-layer multicast
address
- --total-nodes num
- Number of total nodes within this cluster.
- --local-node num
- Local node number within this cluster.
- --hash-init rnd
- Specify the random seed used for hash initialization.
This module sets the netfilter mark value associated with a connection. The mark
is 32 bits wide.
- --set-xmark value[/mask]
- Zero out the bits given by mask and XOR value into the
ctmark.
- --save-mark [--nfmask nfmask] [--ctmask
ctmask]
- Copy the packet mark (nfmark) to the connection mark (ctmark) using the
given masks. The new nfmark value is determined as follows:
- ctmark = (ctmark & ~ctmask) ^ (nfmark & nfmask)
- i.e. ctmask defines what bits to clear and nfmask what bits
of the nfmark to XOR into the ctmark. ctmask and nfmask
default to 0xFFFFFFFF.
- --restore-mark [--nfmask nfmask] [--ctmask
ctmask]
- Copy the connection mark (ctmark) to the packet mark (nfmark) using the
given masks. The new ctmark value is determined as follows:
- nfmark = (nfmark & ~nfmask) ^ (ctmark &
ctmask);
- i.e. nfmask defines what bits to clear and ctmask what bits
of the ctmark to XOR into the nfmark. ctmask and nfmask
default to 0xFFFFFFFF.
- --restore-mark is only valid in the mangle table.
The following mnemonics are available for --set-xmark:
- --and-mark bits
- Binary AND the ctmark with bits. (Mnemonic for --set-xmark
0/invbits, where invbits is the binary negation of
bits.)
- --or-mark bits
- Binary OR the ctmark with bits. (Mnemonic for --set-xmark
bits/bits.)
- --xor-mark bits
- Binary XOR the ctmark with bits. (Mnemonic for --set-xmark
bits/0.)
- --set-mark value[/mask]
- Set the connection mark. If a mask is specified then only those bits set
in the mask are modified.
- --save-mark [--mask mask]
- Copy the nfmark to the ctmark. If a mask is specified, only those bits are
copied.
- --restore-mark [--mask mask]
- Copy the ctmark to the nfmark. If a mask is specified, only those bits are
copied. This is only valid in the mangle table.
This module copies security markings from packets to connections (if unlabeled),
and from connections back to packets (also only if unlabeled). Typically used
in conjunction with SECMARK, it is valid in the security table (for
backwards compatibility with older kernels, it is also valid in the
mangle table).
- --save
- If the packet has a security marking, copy it to the connection if the
connection is not marked.
- --restore
- If the packet does not have a security marking, and the connection does,
copy the security marking from the connection to the packet.
The CT target allows to set parameters for a packet or its associated
connection. The target attaches a "template" connection tracking
entry to the packet, which is then used by the conntrack core when
initializing a new ct entry. This target is thus only valid in the
"raw" table.
- --notrack
- Disables connection tracking for this packet.
- --helper name
- Use the helper identified by name for the connection. This is more
flexible than loading the conntrack helper modules with preset ports.
- --ctevents event[,...]
- Only generate the specified conntrack events for this connection. Possible
event types are: new, related, destroy, reply,
assured, protoinfo, helper, mark (this refers
to the ctmark, not nfmark), natseqinfo, secmark
(ctsecmark).
- --expevents event[,...]
- Only generate the specified expectation events for this connection.
Possible event types are: new.
- --zone-orig {id|mark}
- For traffic coming from ORIGINAL direction, assign this packet to zone
id and only have lookups done in that zone. If mark is used
instead of id, the zone is derived from the packet nfmark.
- --zone-reply {id|mark}
- For traffic coming from REPLY direction, assign this packet to zone
id and only have lookups done in that zone. If mark is used
instead of id, the zone is derived from the packet nfmark.
- --zone {id|mark}
- Assign this packet to zone id and only have lookups done in that
zone. If mark is used instead of id, the zone is derived
from the packet nfmark. By default, packets have zone 0. This option
applies to both directions.
- --timeout name
- Use the timeout policy identified by name for the connection. This
is provides more flexible timeout policy definition than global timeout
values available at /proc/sys/net/netfilter/nf_conntrack_*_timeout_*.
This target is only valid in the nat table, in the PREROUTING and
OUTPUT chains, and user-defined chains which are only called from those
chains. It specifies that the destination address of the packet should be
modified (and all future packets in this connection will also be mangled), and
rules should cease being examined. It takes the following options:
- --to-destination
[ipaddr[-ipaddr]][:port[-port]]
- which can specify a single new destination IP address, an inclusive range
of IP addresses. Optionally a port range, if the rule also specifies one
of the following protocols: tcp, udp, dccp or
sctp. If no port range is specified, then the destination port will
never be modified. If no IP address is specified then only the destination
port will be modified. In Kernels up to 2.6.10 you can add several
--to-destination options. For those kernels, if you specify more than one
destination address, either via an address range or multiple
--to-destination options, a simple round-robin (one after another in
cycle) load balancing takes place between these addresses. Later Kernels
(>= 2.6.11-rc1) don't have the ability to NAT to multiple ranges
anymore.
- --random
- If option --random is used then port mapping will be randomized
(kernel >= 2.6.22).
- --persistent
- Gives a client the same source-/destination-address for each connection.
This supersedes the SAME target. Support for persistent mappings is
available from 2.6.29-rc2.
- IPv6 support available since Linux kernels >= 3.7.
Provides stateless destination IPv6-to-IPv6 Network Prefix Translation (as
described by RFC 6296).
You have to use this target in the mangle table, not in the
nat table. It takes the following options:
- --src-pfx [prefix/length]
- Set source prefix that you want to translate and length
- --dst-pfx [prefix/length]
- Set destination prefix that you want to use in the translation and
length
You have to use the SNPT target to undo the translation.
Example:
- ip6tables -t mangle -I POSTROUTING -s fd00::/64 -o vboxnet0 -j SNPT
--src-pfx fd00::/64 --dst-pfx 2001:e20:2000:40f::/64
- ip6tables -t mangle -I PREROUTING -i wlan0 -d 2001:e20:2000:40f::/64 -j
DNPT --src-pfx 2001:e20:2000:40f::/64 --dst-pfx fd00::/64
You may need to enable IPv6 neighbor proxy:
- sysctl -w net.ipv6.conf.all.proxy_ndp=1
You also have to use the NOTRACK target to disable
connection tracking for translated flows.
This target allows to alter the value of the DSCP bits within the TOS header of
the IPv4 packet. As this manipulates a packet, it can only be used in the
mangle table.
- --set-dscp value
- Set the DSCP field to a numerical value (can be decimal or hex)
- --set-dscp-class class
- Set the DSCP field to a DiffServ class.
This target allows to selectively work around known ECN blackholes. It can only
be used in the mangle table.
- --ecn-tcp-remove
- Remove all ECN bits from the TCP header. Of course, it can only be used in
conjunction with -p tcp.
This is used to modify the Hop Limit field in IPv6 header. The Hop Limit field
is similar to what is known as TTL value in IPv4. Setting or incrementing the
Hop Limit field can potentially be very dangerous, so it should be avoided at
any cost. This target is only valid in mangle table.
Don't ever set or increment the value on packets that leave
your local network!
- --hl-set value
- Set the Hop Limit to `value'.
- --hl-dec value
- Decrement the Hop Limit `value' times.
- --hl-inc value
- Increment the Hop Limit `value' times.
Like MARK, i.e. set the fwmark, but the mark is calculated from hashing packet
selector at choice. You have also to specify the mark range and, optionally,
the offset to start from. ICMP error messages are inspected and used to
calculate the hashing.
Existing options are:
- --hmark-tuple tuple
- Possible tuple members are: src meaning source address (IPv4, IPv6
address), dst meaning destination address (IPv4, IPv6 address),
sport meaning source port (TCP, UDP, UDPlite, SCTP, DCCP),
dport meaning destination port (TCP, UDP, UDPlite, SCTP, DCCP),
spi meaning Security Parameter Index (AH, ESP), and ct
meaning the usage of the conntrack tuple instead of the packet
selectors.
- --hmark-mod value (must be > 0)
- Modulus for hash calculation (to limit the range of possible marks)
- --hmark-offset value
- Offset to start marks from.
- For advanced usage, instead of using --hmark-tuple, you can specify
custom
- prefixes and masks:
- --hmark-src-prefix cidr
- The source address mask in CIDR notation.
- --hmark-dst-prefix cidr
- The destination address mask in CIDR notation.
- --hmark-sport-mask value
- A 16 bit source port mask in hexadecimal.
- --hmark-dport-mask value
- A 16 bit destination port mask in hexadecimal.
- --hmark-spi-mask value
- A 32 bit field with spi mask.
- --hmark-proto-mask value
- An 8 bit field with layer 4 protocol number.
- --hmark-rnd value
- A 32 bit random custom value to feed hash calculation.
Examples:
iptables -t mangle -A PREROUTING -m conntrack --ctstate NEW
-j HMARK --hmark-tuple ct,src,dst,proto --hmark-offset 10000 --hmark-mod 10
--hmark-rnd 0xfeedcafe
iptables -t mangle -A PREROUTING -j HMARK --hmark-offset 10000
--hmark-tuple src,dst,proto --hmark-mod 10 --hmark-rnd 0xdeafbeef
This target can be used to identify when interfaces have been idle for a certain
period of time. Timers are identified by labels and are created when a rule is
set with a new label. The rules also take a timeout value (in seconds) as an
option. If more than one rule uses the same timer label, the timer will be
restarted whenever any of the rules get a hit. One entry for each timer is
created in sysfs. This attribute contains the timer remaining for the timer to
expire. The attributes are located under the xt_idletimer class:
/sys/class/xt_idletimer/timers/<label>
When the timer expires, the target module sends a sysfs
notification to the userspace, which can then decide what to do (eg.
disconnect to save power).
- --timeout amount
- This is the time in seconds that will trigger the notification.
- --label string
- This is a unique identifier for the timer. The maximum length for the
label string is 27 characters.
This creates an LED-trigger that can then be attached to system indicator
lights, to blink or illuminate them when certain packets pass through the
system. One example might be to light up an LED for a few minutes every time
an SSH connection is made to the local machine. The following options control
the trigger behavior:
- --led-trigger-id name
- This is the name given to the LED trigger. The actual name of the trigger
will be prefixed with "netfilter-".
- --led-delay ms
- This indicates how long (in milliseconds) the LED should be left
illuminated when a packet arrives before being switched off again. The
default is 0 (blink as fast as possible.) The special value inf can
be given to leave the LED on permanently once activated. (In this case the
trigger will need to be manually detached and reattached to the LED device
to switch it off again.)
- --led-always-blink
- Always make the LED blink on packet arrival, even if the LED is already
on. This allows notification of new packets even with long delay values
(which otherwise would result in a silent prolonging of the delay
time.)
- Example:
- Create an LED trigger for incoming SSH traffic:
- iptables -A INPUT -p tcp --dport 22 -j LED --led-trigger-id ssh
- Then attach the new trigger to an LED:
- echo netfilter-ssh >/sys/class/leds/ledname/trigger
Turn on kernel logging of matching packets. When this option is set for a rule,
the Linux kernel will print some information on all matching packets (like
most IP/IPv6 header fields) via the kernel log (where it can be read with
dmesg(1) or read in the syslog).
This is a "non-terminating target", i.e. rule traversal
continues at the next rule. So if you want to LOG the packets you refuse,
use two separate rules with the same matching criteria, first using target
LOG then DROP (or REJECT).
- --log-level level
- Level of logging, which can be (system-specific) numeric or a mnemonic.
Possible values are (in decreasing order of priority): emerg,
alert, crit, error, warning, notice,
info or debug.
- --log-prefix prefix
- Prefix log messages with the specified prefix; up to 29 letters long, and
useful for distinguishing messages in the logs.
- --log-tcp-sequence
- Log TCP sequence numbers. This is a security risk if the log is readable
by users.
- --log-tcp-options
- Log options from the TCP packet header.
- --log-ip-options
- Log options from the IP/IPv6 packet header.
- --log-uid
- Log the userid of the process which generated the packet.
This target is used to set the Netfilter mark value associated with the packet.
It can, for example, be used in conjunction with routing based on fwmark
(needs iproute2). If you plan on doing so, note that the mark needs to be set
in the PREROUTING chain of the mangle table to affect routing. The mark field
is 32 bits wide.
- --set-xmark value[/mask]
- Zeroes out the bits given by mask and XORs value into the
packet mark ("nfmark"). If mask is omitted, 0xFFFFFFFF is
assumed.
- --set-mark value[/mask]
- Zeroes out the bits given by mask and ORs value into the
packet mark. If mask is omitted, 0xFFFFFFFF is assumed.
The following mnemonics are available:
- --and-mark bits
- Binary AND the nfmark with bits. (Mnemonic for --set-xmark
0/invbits, where invbits is the binary negation of
bits.)
- --or-mark bits
- Binary OR the nfmark with bits. (Mnemonic for --set-xmark
bits/bits.)
- --xor-mark bits
- Binary XOR the nfmark with bits. (Mnemonic for --set-xmark
bits/0.)
This target is only valid in the nat table, in the POSTROUTING
chain. It should only be used with dynamically assigned IP (dialup)
connections: if you have a static IP address, you should use the SNAT target.
Masquerading is equivalent to specifying a mapping to the IP address of the
interface the packet is going out, but also has the effect that connections
are forgotten when the interface goes down. This is the correct
behavior when the next dialup is unlikely to have the same interface address
(and hence any established connections are lost anyway).
- --to-ports port[-port]
- This specifies a range of source ports to use, overriding the default
SNAT source port-selection heuristics (see above). This is only
valid if the rule also specifies one of the following protocols:
tcp, udp, dccp or sctp.
- --random
- Randomize source port mapping If option --random is used then port
mapping will be randomized (kernel >= 2.6.21). Since kernel 5.0,
--random is identical to --random-fully.
- --random-fully
- Full randomize source port mapping If option --random-fully is used
then port mapping will be fully randomized (kernel >= 3.13).
- IPv6 support available since Linux kernels >= 3.7.
This target allows you to statically map a whole network of addresses onto
another network of addresses. It can only be used from rules in the nat
table.
- --to address[/mask]
- Network address to map to. The resulting address will be constructed in
the following way: All 'one' bits in the mask are filled in from the new
`address'. All bits that are zero in the mask are filled in from the
original address.
- IPv6 support available since Linux kernels >= 3.7.
This target provides logging of matching packets. When this target is set for a
rule, the Linux kernel will pass the packet to the loaded logging backend to
log the packet. This is usually used in combination with nfnetlink_log as
logging backend, which will multicast the packet through a netlink
socket to the specified multicast group. One or more userspace processes may
subscribe to the group to receive the packets. Like LOG, this is a
non-terminating target, i.e. rule traversal continues at the next rule.
- --nflog-group nlgroup
- The netlink group (0 - 2^16-1) to which packets are (only applicable for
nfnetlink_log). The default value is 0.
- --nflog-prefix prefix
- A prefix string to include in the log message, up to 64 characters long,
useful for distinguishing messages in the logs.
- --nflog-range size
- This option has never worked, use --nflog-size instead
- --nflog-size size
- The number of bytes to be copied to userspace (only applicable for
nfnetlink_log). nfnetlink_log instances may specify their own range, this
option overrides it.
- --nflog-threshold size
- Number of packets to queue inside the kernel before sending them to
userspace (only applicable for nfnetlink_log). Higher values result in
less overhead per packet, but increase delay until the packets reach
userspace. The default value is 1.
This target passes the packet to userspace using the nfnetlink_queue
handler. The packet is put into the queue identified by its 16-bit queue
number. Userspace can inspect and modify the packet if desired. Userspace must
then drop or reinject the packet into the kernel. Please see
libnetfilter_queue for details. nfnetlink_queue was added in Linux
2.6.14. The queue-balance option was added in Linux 2.6.31,
queue-bypass in 2.6.39.
- --queue-num value
- This specifies the QUEUE number to use. Valid queue numbers are 0 to
65535. The default value is 0.
- --queue-balance value:value
- This specifies a range of queues to use. Packets are then balanced across
the given queues. This is useful for multicore systems: start multiple
instances of the userspace program on queues x, x+1, .. x+n and use
"--queue-balance x:x+n". Packets belonging
to the same connection are put into the same nfqueue.
- --queue-bypass
- By default, if no userspace program is listening on an NFQUEUE, then all
packets that are to be queued are dropped. When this option is used, the
NFQUEUE rule behaves like ACCEPT instead, and the packet will move on to
the next table.
- --queue-cpu-fanout
- Available starting Linux kernel 3.10. When used together with
--queue-balance this will use the CPU ID as an index to map packets
to the queues. The idea is that you can improve performance if there's a
queue per CPU. This requires --queue-balance to be specified.
This extension disables connection tracking for all packets matching that rule.
It is equivalent with -j CT --notrack. Like CT, NOTRACK can only be used in
the raw table.
The RATEEST target collects statistics, performs rate estimation calculation and
saves the results for later evaluation using the rateest match.
- --rateest-name name
- Count matched packets into the pool referred to by name, which is
freely choosable.
- --rateest-interval amount{s|ms|us}
- Rate measurement interval, in seconds, milliseconds or microseconds.
- --rateest-ewmalog value
- Rate measurement averaging time constant.
This target is only valid in the nat table, in the PREROUTING and
OUTPUT chains, and user-defined chains which are only called from those
chains. It redirects the packet to the machine itself by changing the
destination IP to the primary address of the incoming interface
(locally-generated packets are mapped to the localhost address, <IP_ADDRESS> for
IPv4 and ::1 for IPv6, and packets arriving on interfaces that don't have an
IP address configured are dropped).
- --to-ports port[-port]
- This specifies a destination port or range of ports to use: without this,
the destination port is never altered. This is only valid if the rule also
specifies one of the following protocols: tcp, udp,
dccp or sctp.
- --random
- If option --random is used then port mapping will be randomized
(kernel >= 2.6.22).
- IPv6 support available starting Linux kernels >= 3.7.
This is used to send back an error packet in response to the matched packet:
otherwise it is equivalent to DROP so it is a terminating TARGET,
ending rule traversal. This target is only valid in the INPUT,
FORWARD and OUTPUT chains, and user-defined chains which are
only called from those chains. The following option controls the nature of the
error packet returned:
- --reject-with type
- The type given can be icmp6-no-route, no-route,
icmp6-adm-prohibited, adm-prohibited,
icmp6-addr-unreachable, addr-unreach, or
icmp6-port-unreachable, which return the appropriate ICMPv6 error
message (icmp6-port-unreachable is the default). Finally, the
option tcp-reset can be used on rules which only match the TCP
protocol: this causes a TCP RST packet to be sent back. This is mainly
useful for blocking ident (113/tcp) probes which frequently occur
when sending mail to broken mail hosts (which won't accept your mail
otherwise). tcp-reset can only be used with kernel versions 2.6.14
or later.
This is used to send back an error packet in response to the matched packet:
otherwise it is equivalent to DROP so it is a terminating TARGET,
ending rule traversal. This target is only valid in the INPUT,
FORWARD and OUTPUT chains, and user-defined chains which are
only called from those chains. The following option controls the nature of the
error packet returned:
- --reject-with type
- The type given can be icmp-net-unreachable,
icmp-host-unreachable, icmp-port-unreachable,
icmp-proto-unreachable, icmp-net-prohibited,
icmp-host-prohibited, or icmp-admin-prohibited (*), which
return the appropriate ICMP error message (icmp-port-unreachable is
the default). The option tcp-reset can be used on rules which only
match the TCP protocol: this causes a TCP RST packet to be sent back. This
is mainly useful for blocking ident (113/tcp) probes which
frequently occur when sending mail to broken mail hosts (which won't
accept your mail otherwise).
- (*) Using icmp-admin-prohibited with kernels that do not support it will
result in a plain DROP instead of REJECT
This is used to set the security mark value associated with the packet for use
by security subsystems such as SELinux. It is valid in the security
table (for backwards compatibility with older kernels, it is also valid in the
mangle table). The mark is 32 bits wide.
- --selctx security_context
This module adds and/or deletes entries from IP sets which can be defined by
ipset(8).
- --add-set setname flag[,flag...]
- add the address(es)/port(s) of the packet to the set
- --del-set setname flag[,flag...]
- delete the address(es)/port(s) of the packet from the set
- --map-set setname flag[,flag...]
- [--map-mark] [--map-prio] [--map-queue] map packet properties (firewall
mark, tc priority, hardware queue)
- where flag(s) are src and/or dst specifications and
there can be no more than six of them.
- --timeout value
- when adding an entry, the timeout value to use instead of the default one
from the set definition
- --exist
- when adding an entry if it already exists, reset the timeout value to the
specified one or to the default from the set definition
- --map-set set-name
- the set-name should be created with --skbinfo option --map-mark map
firewall mark to packet by lookup of value in the set --map-prio
map traffic control priority to packet by lookup of value in the set
--map-queue map hardware NIC queue to packet by lookup of value in
the set
- The --map-set option can be used from the mangle table only. The
--map-prio and --map-queue flags can be used in the OUTPUT,
FORWARD and POSTROUTING chains.
Use of -j SET requires that ipset kernel support is provided,
which, for standard kernels, is the case since Linux 2.6.39.
This target is only valid in the nat table, in the POSTROUTING and
INPUT chains, and user-defined chains which are only called from those
chains. It specifies that the source address of the packet should be modified
(and all future packets in this connection will also be mangled), and rules
should cease being examined. It takes the following options:
- --to-source
[ipaddr[-ipaddr]][:port[-port]]
- which can specify a single new source IP address, an inclusive range of IP
addresses. Optionally a port range, if the rule also specifies one of the
following protocols: tcp, udp, dccp or sctp.
If no port range is specified, then source ports below 512 will be mapped
to other ports below 512: those between 512 and 1023 inclusive will be
mapped to ports below 1024, and other ports will be mapped to 1024 or
above. Where possible, no port alteration will occur. In Kernels up to
2.6.10, you can add several --to-source options. For those kernels, if you
specify more than one source address, either via an address range or
multiple --to-source options, a simple round-robin (one after another in
cycle) takes place between these addresses. Later Kernels (>=
2.6.11-rc1) don't have the ability to NAT to multiple ranges anymore.
- --random
- If option --random is used then port mapping will be randomized
through a hash-based algorithm (kernel >= 2.6.21).
- --random-fully
- If option --random-fully is used then port mapping will be fully
randomized through a PRNG (kernel >= 3.14).
- --persistent
- Gives a client the same source-/destination-address for each connection.
This supersedes the SAME target. Support for persistent mappings is
available from 2.6.29-rc2.
Kernels prior to 2.6.36-rc1 don't have the ability to SNAT
in the INPUT chain.
- IPv6 support available since Linux kernels >= 3.7.
Provides stateless source IPv6-to-IPv6 Network Prefix Translation (as described
by RFC 6296).
You have to use this target in the mangle table, not in the
nat table. It takes the following options:
- --src-pfx [prefix/length]
- Set source prefix that you want to translate and length
- --dst-pfx [prefix/length]
- Set destination prefix that you want to use in the translation and
length
You have to use the DNPT target to undo the translation.
Example:
- ip6tables -t mangle -I POSTROUTING -s fd00::/64 -o vboxnet0 -j SNPT
--src-pfx fd00::/64 --dst-pfx 2001:e20:2000:40f::/64
- ip6tables -t mangle -I PREROUTING -i wlan0 -d 2001:e20:2000:40f::/64 -j
DNPT --src-pfx 2001:e20:2000:40f::/64 --dst-pfx fd00::/64
You may need to enable IPv6 neighbor proxy:
- sysctl -w net.ipv6.conf.all.proxy_ndp=1
You also have to use the NOTRACK target to disable
connection tracking for translated flows.
This target will process TCP three-way-handshake parallel in netfilter context
to protect either local or backend system. This target requires connection
tracking because sequence numbers need to be translated. The kernels ability
to absorb SYNFLOOD was greatly improved starting with Linux 4.4, so this
target should not be needed anymore to protect Linux servers.
- --mss maximum segment size
- Maximum segment size announced to clients. This must match the
backend.
- --wscale window scale
- Window scale announced to clients. This must match the backend.
- --sack-perm
- Pass client selective acknowledgement option to backend (will be disabled
if not present).
- --timestamps
- Pass client timestamp option to backend (will be disabled if not present,
also needed for selective acknowledgement and window scaling).
Example:
Determine tcp options used by backend, from an external system
- tcpdump -pni eth0 -c 1 'tcp[tcpflags] == (tcp-syn|tcp-ack)'
port 80 &
telnet <IP_ADDRESS> 80
18:57:24.693307 IP <IP_ADDRESS>.80 > <IP_ADDRESS>.48757:
Flags [S.], seq 360414582, ack 788841994, win 14480,
options [mss 1460,sackOK,
TS val<PHONE_NUMBER> ecr 9690221,
nop,wscale 9],
length 0
Switch tcp_loose mode off, so conntrack will mark out-of-flow
packets as state INVALID.
- echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose
Make SYN packets untracked
- iptables -t raw -A PREROUTING -i eth0 -p tcp --dport 80
--syn -j CT --notrack
Catch UNTRACKED (SYN packets) and INVALID (3WHS ACK packets)
states and send them to SYNPROXY. This rule will respond to SYN packets with
SYN+ACK syncookies, create ESTABLISHED for valid client response (3WHS ACK
packets) and drop incorrect cookies. Flags combinations not expected during
3WHS will not match and continue (e.g. SYN+FIN, SYN+ACK).
- iptables -A INPUT -i eth0 -p tcp --dport 80
-m state --state UNTRACKED,INVALID -j SYNPROXY
--sack-perm --timestamp --mss 1460 --wscale 9
Drop invalid packets, this will be out-of-flow packets that were
not matched by SYNPROXY.
- iptables -A INPUT -i eth0 -p tcp --dport 80 -m state --state INVALID -j
DROP
This target allows to alter the MSS value of TCP SYN packets, to control the
maximum size for that connection (usually limiting it to your outgoing
interface's MTU minus 40 for IPv4 or 60 for IPv6, respectively). Of course, it
can only be used in conjunction with -p tcp.
This target is used to overcome criminally braindead ISPs or
servers which block "ICMP Fragmentation Needed" or "ICMPv6
Packet Too Big" packets. The symptoms of this problem are that
everything works fine from your Linux firewall/router, but machines behind
it can never exchange large packets:
- 1.
- Web browsers connect, then hang with no data received.
- 2.
- Small mail works fine, but large emails hang.
- 3.
- ssh works fine, but scp hangs after initial handshaking.
Workaround: activate this option and add a rule to your firewall
configuration like:
-
iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN
-j TCPMSS --clamp-mss-to-pmtu
- --set-mss value
- Explicitly sets MSS option to specified value. If the MSS of the packet is
already lower than value, it will not be increased (from
Linux 2.6.25 onwards) to avoid more problems with hosts relying on a
proper MSS.
- --clamp-mss-to-pmtu
- Automatically clamp MSS value to (path_MTU - 40 for IPv4; -60 for IPv6).
This may not function as desired where asymmetric routes with differing
path MTU exist — the kernel uses the path MTU which it would use to
send packets from itself to the source and destination IP addresses. Prior
to Linux 2.6.25, only the path MTU to the destination IP address was
considered by this option; subsequent kernels also consider the path MTU
to the source IP address.
These options are mutually exclusive.
This target will strip TCP options off a TCP packet. (It will actually replace
them by NO-OPs.) As such, you will need to add the -p tcp parameters.
- --strip-options option[,option...]
- Strip the given option(s). The options may be specified by TCP option
number or by symbolic name. The list of recognized options can be obtained
by calling iptables with -j TCPOPTSTRIP -h.
The TEE target will clone a packet and redirect this clone to another
machine on the local network segment. In other words, the nexthop must
be the target, or you will have to configure the nexthop to forward it further
if so desired.
- --gateway ipaddr
- Send the cloned packet to the host reachable at the given IP address. Use
of <IP_ADDRESS> (for IPv4 packets) or :: (IPv6) is invalid.
To forward all incoming traffic on eth0 to an Network Layer
logging box:
-t mangle -A PREROUTING -i eth0 -j TEE --gateway 2001:db8::1
This module sets the Type of Service field in the IPv4 header (including the
"precedence" bits) or the Priority field in the IPv6 header. Note
that TOS shares the same bits as DSCP and ECN. The TOS target is only valid in
the mangle table.
- --set-tos value[/mask]
- Zeroes out the bits given by mask (see NOTE below) and XORs
value into the TOS/Priority field. If mask is omitted, 0xFF
is assumed.
- --set-tos symbol
- You can specify a symbolic name when using the TOS target for IPv4. It
implies a mask of 0xFF (see NOTE below). The list of recognized TOS names
can be obtained by calling iptables with -j TOS -h.
The following mnemonics are available:
- --and-tos bits
- Binary AND the TOS value with bits. (Mnemonic for --set-tos
0/invbits, where invbits is the binary negation of
bits. See NOTE below.)
- --or-tos bits
- Binary OR the TOS value with bits. (Mnemonic for --set-tos
bits/bits. See NOTE below.)
- --xor-tos bits
- Binary XOR the TOS value with bits. (Mnemonic for --set-tos
bits/0. See NOTE below.)
NOTE: In Linux kernels up to and including 2.6.38, with the
exception of longterm releases 2.6.32 (>=.42), 2.6.33 (>=.15), and
2.6.35 (>=.14), there is a bug whereby IPv6 TOS mangling does not behave
as documented and differs from the IPv4 version. The TOS mask indicates the
bits one wants to zero out, so it needs to be inverted before applying it to
the original TOS field. However, the aformentioned kernels forgo the
inversion which breaks --set-tos and its mnemonics.
This target is only valid in the mangle table, in the PREROUTING
chain and user-defined chains which are only called from this chain. It
redirects the packet to a local socket without changing the packet header in
any way. It can also change the mark value which can then be used in advanced
routing rules. It takes three options:
- --on-port port
- This specifies a destination port to use. It is a required option, 0 means
the new destination port is the same as the original. This is only valid
if the rule also specifies -p tcp or -p udp.
- --on-ip address
- This specifies a destination address to use. By default the address is the
IP address of the incoming interface. This is only valid if the rule also
specifies -p tcp or -p udp.
- --tproxy-mark value[/mask]
- Marks packets with the given value/mask. The fwmark value set here can be
used by advanced routing. (Required for transparent proxying to work:
otherwise these packets will get forwarded, which is probably not what you
want.)
This target marks packets so that the kernel will log every rule which match the
packets as those traverse the tables, chains, rules. It can only be used in
the raw table.
With iptables-legacy, a logging backend, such as ip(6)t_LOG or
nfnetlink_log, must be loaded for this to be visible. The packets are logged
with the string prefix: "TRACE: tablename:chainname:type:rulenum "
where type can be "rule" for plain rule, "return" for
implicit rule at the end of a user defined chain and "policy" for
the policy of the built in chains.
With iptables-nft, the target is translated into nftables' meta
nftrace expression. Hence the kernel sends trace events via netlink to
userspace where they may be displayed using xtables-monitor --trace
command. For details, refer to xtables-monitor(8).
This is used to modify the IPv4 TTL header field. The TTL field determines how
many hops (routers) a packet can traverse until it's time to live is exceeded.
Setting or incrementing the TTL field can potentially be very
dangerous, so it should be avoided at any cost. This target is only valid in
mangle table.
Don't ever set or increment the value on packets that leave
your local network!
- --ttl-set value
- Set the TTL value to `value'.
- --ttl-dec value
- Decrement the TTL value `value' times.
- --ttl-inc value
- Increment the TTL value `value' times.
This is the deprecated ipv4-only predecessor of the NFLOG target. It provides
userspace logging of matching packets. When this target is set for a rule, the
Linux kernel will multicast this packet through a netlink socket. One
or more userspace processes may then subscribe to various multicast groups and
receive the packets. Like LOG, this is a "non-terminating target",
i.e. rule traversal continues at the next rule.
- --ulog-nlgroup nlgroup
- This specifies the netlink group (1-32) to which the packet is sent.
Default value is 1.
- --ulog-prefix prefix
- Prefix log messages with the specified prefix; up to 32 characters long,
and useful for distinguishing messages in the logs.
- --ulog-cprange size
- Number of bytes to be copied to userspace. A value of 0 always copies the
entire packet, regardless of its size. Default is 0.
- --ulog-qthreshold size
- Number of packet to queue inside kernel. Setting this value to, e.g. 10
accumulates ten packets inside the kernel and transmits them as one
netlink multipart message to userspace. Default is 1 (for backwards
compatibility).


- Iframe :
The  tag defines a rectangular region within the document in which the browser can display a separate document, including scrollbars and borders. An inline frame is used to embed another document within the current HTML document.
Example
Iframe Syntax
An HTML iframe is defined with the  tag:

The "src" attribute specifies the URL (web address) of the inline frame page.
Iframe - Set Height and Width
Use the height and width attributes to specify the size of the iframe.
The attribute values are specified in pixels by default, but they can also be in percent (like "80%").
Example
Code :

OR

Iframe - Remove the Border
By default, an iframe has a border around it. To remove the border, add the "style" attribute and use the CSS "border" property:
Example
Code :

Iframe - Adding the Border
With CSS, you can also change the size, style and color of the iframe's border:
Code :

Iframe - Target for a Link
An iframe can be used as the target frame for a link. The "target" attribute of the link must refer to the "name" attribute of the iframe:
Example
Click Me !!!
Code :

Click Me !!!

End of Iframe
- Framset :
HTML frames are used to divide your browser window into multiple sections where each section can load a separate HTML document. A collection of frames in the browser window is known as a frameset. The window is divided into frames in a similar way the tables are organized: into rows and columns.
Example
Code :
<frameset cols="30%,*,30%">
<frame src = "a.html">
<frame src = "b.html">
<frame src = "c.html">
</frameset>
This Window is Resizable...
Frameset - Noresize Property
The "noresize" Property is used to block the Frame resizing by the User.
Example
Code :
<frameset cols="30%,*,30%">
<frame src = "a.html" noresize>
<frame src = "b.html" noresize>
<frame src = "c.html" noresize>
</frameset>
This Window is Non - Resizable...
End of Frameset