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NAME

iptables - administration tool for IPv4 packet filtering and NAT
 

SYNOPSIS

DESCRIPTION

Each chain is a list of rules which can match a set of packets. Each rule specifies what to do with a packet that matches. This is called a `target', which may be a jump to a user-defined chain in the same table.

TARGETS

ACCEPT means to let the packet through. DROP means to drop the packet on the floor. QUEUE means to pass the packet to userspace. (How the packet can be received by a userspace process differs by the particular queue handler. 2.4.x and 2.6.x kernels up to 2.6.13 include the ip_queue queue handler. Kernels 2.6.14 and later additionally include the nfnetlink_queue queue handler. Packets with a target of QUEUE will be sent to queue number '0' in this case. Please also see the NFQUEUE target as described later in this man page.) RETURN means stop traversing this chain and resume at the next rule in the previous (calling) chain. If the end of a built-in chain is reached or a rule in a built-in chain with target RETURN is matched, the target specified by the chain policy determines the fate of the packet.  

TABLES

-t, --table table

This option specifies the packet matching table which the command should operate on. If the kernel is configured with automatic module loading, an attempt will be made to load the appropriate module for that table if it is not already there.

The tables are as follows:

filter:

This is the default table (if no -t option is passed). It contains the built-in chains INPUT (for packets destined to local sockets), FORWARD (for packets being routed through the box), and OUTPUT (for locally-generated packets).

nat:

This table is consulted when a packet that creates a new connection is encountered. It consists of three built-ins: PREROUTING (for altering packets as soon as they come in), OUTPUT (for altering locally-generated packets before routing), and POSTROUTING (for altering packets as they are about to go out).

mangle:

This table is used for specialized packet alteration. Until kernel 2.4.17 it had two built-in chains: PREROUTING (for altering incoming packets before routing) and OUTPUT (for altering locally-generated packets before routing). Since kernel 2.4.18, three other built-in chains are also supported: INPUT (for packets coming into the box itself), FORWARD (for altering packets being routed through the box), and POSTROUTING (for altering packets as they are about to go out).

raw:

This table is used mainly for configuring exemptions from connection tracking in combination with the NOTRACK target. It registers at the netfilter hooks with higher priority and is thus called before ip_conntrack, or any other IP tables. It provides the following built-in chains: PREROUTING (for packets arriving via any network interface) OUTPUT (for packets generated by local processes)

OPTIONS

COMMANDS

-A, --append chain rule-specification

Append one or more rules to the end of the selected chain. When the source and/or destination names resolve to more than one address, a rule will be added for each possible address combination.

-D, --delete chain rule-specification

-D, --delete chain rulenum

Delete one or more rules from the selected chain. There are two versions of this command: the rule can be specified as a number in the chain (starting at 1 for the first rule) or a rule to match.

-I, --insert chain [rulenum] rule-specification

Insert one or more rules in the selected chain as the given rule number. So, if the rule number is 1, the rule or rules are inserted at the head of the chain. This is also the default if no rule number is specified.

-R, --replace chain rulenum rule-specification

Replace a rule in the selected chain. If the source and/or destination names resolve to multiple addresses, the command will fail. Rules are numbered starting at 1.

-L, --list [chain]

List all rules in the selected chain. If no chain is selected, all chains are listed. As every other iptables command, it applies to the specified table (filter is the default), so NAT rules get listed by

 iptables -t nat -n -L

Please note that it is often used with the -n option, in order to avoid long reverse DNS lookups. It is legal to specify the -Z (zero) option as well, in which case the chain(s) will be atomically listed and zeroed. The exact output is affected by the other arguments given. The exact rules are suppressed until you use

 iptables -L -v

-F, --flush [chain]

Flush the selected chain (all the chains in the table if none is given). This is equivalent to deleting all the rules one by one.

-Z, --zero [chain]

Zero the packet and byte counters in all chains. It is legal to specify the -L, --list (list) option as well, to see the counters immediately before they are cleared. (See above.)

-N, --new-chain chain

Create a new user-defined chain by the given name. There must be no target of that name already.

-X, --delete-chain [chain]

Delete the optional user-defined chain specified. There must be no references to the chain. If there are, you must delete or replace the referring rules before the chain can be deleted. The chain must be empty, i.e. not contain any rules. If no argument is given, it will attempt to delete every non-builtin chain in the table.

-P, --policy chain target

Set the policy for the chain to the given target. See the section TARGETS for the legal targets. Only built-in (non-user-defined) chains can have policies, and neither built-in nor user-defined chains can be policy targets.

-E, --rename-chain old-chain new-chain

Rename the user specified chain to the user supplied name. This is cosmetic, and has no effect on the structure of the table.

-h

Help. Give a (currently very brief) description of the command syntax.

PARAMETERS

-p, --protocol [!] protocol

The protocol of the rule or of the packet to check. The specified protocol can be one of tcp, udp, icmp, or all, or it can be a numeric value, representing one of these protocols or a different one. A protocol name from /etc/protocols is also allowed. A "!" argument before the protocol inverts the test. The number zero is equivalent to all. Protocol all will match with all protocols and is taken as default when this option is omitted.

-s, --source [!] address[/mask]

Source specification. Address can be either a network name, a hostname (please note that specifying any name to be resolved with a remote query such as DNS is a really bad idea), a network IP address (with /mask), or a plain IP address. The mask can be either a network mask or a plain number, specifying the number of 1's at the left side of the network mask. Thus, a mask of 24 is equivalent to 255.255.255.0. A "!" argument before the address specification inverts the sense of the address. The flag --src is an alias for this option.

-d, --destination [!] address[/mask]

Destination specification. See the description of the -s (source) flag for a detailed description of the syntax. The flag --dst is an alias for this option.

-j, --jump target

This specifies the target of the rule; i.e., what to do if the packet matches it. The target can be a user-defined chain (other than the one this rule is in), one of the special builtin targets which decide the fate of the packet immediately, or an extension (see EXTENSIONS below). If this option is omitted in a rule (and -g is not used), then matching the rule will have no effect on the packet's fate, but the counters on the rule will be incremented.

-g, --goto chain

This specifies that the processing should continue in a user specified chain. Unlike the --jump option return will not continue processing in this chain but instead in the chain that called us via --jump.

-i, --in-interface [!] name

Name of an interface via which a packet was received (only for packets entering the INPUT, FORWARD and PREROUTING chains). When the "!" argument is used before the interface name, the sense is inverted. If the interface name ends in a "+", then any interface which begins with this name will match. If this option is omitted, any interface name will match.

-o, --out-interface [!] name

Name of an interface via which a packet is going to be sent (for packets entering the FORWARD, OUTPUT and POSTROUTING chains). When the "!" argument is used before the interface name, the sense is inverted. If the interface name ends in a "+", then any interface which begins with this name will match. If this option is omitted, any interface name will match.

[!] -f, --fragment

This means that the rule only refers to second and further fragments of fragmented packets. Since there is no way to tell the source or destination ports of such a packet (or ICMP type), such a packet will not match any rules which specify them. When the "!" argument precedes the "-f" flag, the rule will only match head fragments, or unfragmented packets.

-c, --set-counters PKTS BYTES

This enables the administrator to initialize the packet and byte counters of a rule (during INSERT, APPEND, REPLACE operations).

OTHER OPTIONS

-v, --verbose

Verbose output. This option makes the list command show the interface name, the rule options (if any), and the TOS masks. The packet and byte counters are also listed, with the suffix 'K', 'M' or 'G' for 1000, 1,000,000 and 1,000,000,000 multipliers respectively (but see the -x flag to change this). For appending, insertion, deletion and replacement, this causes detailed information on the rule or rules to be printed.

-n, --numeric

Numeric output. IP addresses and port numbers will be printed in numeric format. By default, the program will try to display them as host names, network names, or services (whenever applicable).

-x, --exact

Expand numbers. Display the exact value of the packet and byte counters, instead of only the rounded number in K's (multiples of 1000) M's (multiples of 1000K) or G's (multiples of 1000M). This option is only relevant for the -L command.

--line-numbers

When listing rules, add line numbers to the beginning of each rule, corresponding to that rule's position in the chain.

--modprobe=command

When adding or inserting rules into a chain, use command to load any necessary modules (targets, match extensions, etc).

MATCH EXTENSIONS

The following are included in the base package, and most of these can be preceded by a ! to invert the sense of the match.  

account

Features:

- long (one counter per protocol TCP/UDP/IMCP/Other) and short statistics

- one iptables rule for all hosts in network/netmask

- loading/saving counters (by reading/writting to procfs entries)

--aaddr network/netmask

defines network/netmask for which make statistics.

--aname name

defines name of list where statistics will be kept. If no is specified DEFAULT will be used.

--ashort

table will colect only short statistics (only total counters without splitting it into protocols. Example usage:

account traffic for/to 192.168.0.0/24 network into table mynetwork:

# iptables -A FORWARD -m account --aname mynetwork --aaddr 192.168.0.0/24

account traffic for/to WWW serwer for 192.168.0.0/24 network into table mywwwserver:

# iptables -A INPUT -p tcp --dport 80
  -m account --aname mywwwserver --aaddr 192.168.0.0/24 --ashort

# iptables -A OUTPUT -p tcp --sport 80
  -m account --aname mywwwserver --aaddr 192.168.0.0/24 --ashort

read counters:

# cat /proc/net/ipt_account/mynetwork # cat /proc/net/ipt_account/mywwwserver

set counters:

# echo "ip = 192.168.0.1 packets_src = 0" > /proc/net/ipt_account/mywwserver

Webpage:
  http://www.barbara.eu.org/~quaker/ipt_account/

addrtype

The following address types are possible:

UNSPEC

an unspecified address (i.e. 0.0.0.0) 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 FIXME

--src-type type

Matches if the source address is of given type

--dst-type type

Matches if the destination address is of given type

ah

--ahspi [!] spi[:spi]

childlevel

--childlevel [!] level

comment

--comment comment

Example:

iptables -A INPUT -s 192.168.0.0/16 -m comment --comment "A privatized IP block"

condition

--condition [!] filename

Match on boolean value stored in /proc/net/ipt_condition/filename file

connbytes

The counters are 64bit 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 transfered bytes per connection can also be viewed through /proc/net/ip_conntrack and accessed via ctnetlink

[!] --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 ...

connlimit

[!] --connlimit-above n

match if the number of existing tcp connections is (not) above n

--connlimit-mask bits

group hosts using mask Examples:

# allow 2 telnet connections per client host

iptables -p tcp --syn --dport 23 -m connlimit --connlimit-above 2 -j REJECT

# you can also match the other way around:

iptables -p tcp --syn --dport 23 -m connlimit ! --connlimit-above 2 -j ACCEPT

# limit the nr of parallel http requests to 16 per class C sized network (24 bit netmask)

iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above 16 --connlimit-mask 24 -j REJECT

connmark

--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).

connrate

--connrate [!] [from]:[to]

Match against the current connection transfer rate being within 'from' and 'to' bytes per second. When the "!" argument is used before the range, the sense of the match is inverted.

conntrack

--ctstate state

Where state is a comma separated list of the connection states to match. Possible states are INVALID meaning that the packet is associated with no known connection, ESTABLISHED meaning that the packet is associated with a connection which has seen packets in both directions, NEW meaning that the packet has started a new connection, or otherwise associated with a connection which has not seen packets in both directions, and RELATED meaning that the packet is starting a new connection, but is associated with an existing connection, such as an FTP data transfer, or an ICMP error. 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.

--ctproto proto

Protocol to match (by number or name)

--ctorigsrc [!] address[/mask]

Match against original source address

--ctorigdst [!] address[/mask]

Match against original destination address

--ctreplsrc [!] address[/mask]

Match against reply source address

--ctrepldst [!] address[/mask]

Match against reply destination address

--ctstatus [NONE|EXPECTED|SEEN_REPLY|ASSURED][,...]

Match against internal conntrack states

--ctexpire time[:time]

Match remaining lifetime in seconds against given value or range of values (inclusive)

dccp

--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 DCP option set.

dscp

--dscp value

Match against a numeric (decimal or hex) value [0-32].

--dscp-class DiffServ Class

Match the DiffServ class. This value may be any of the BE, EF, AFxx or CSx classes. It will then be converted into it's according numeric value.

dstlimit

THIS MODULE IS DEPRECATED AND HAS BEEN REPLACED BY ``hashlimit''

--dstlimit avg

Maximum average match rate (packets per second unless followed by /sec /minute /hour /day postfixes).

--dstlimit-mode mode

The limiting hashmode. Is the specified limit per dstip, dstip-dstport tuple, srcip-dstip tuple, or per srcipdstip-dstport tuple.

--dstlimit-name name

Name for /proc/net/ipt_dstlimit/* file entry

[--dstlimit-burst burst]

Number of packets to match in a burst. Default: 5

[--dstlimit-htable-size size]

Number of buckets in the hashtable

[--dstlimit-htable-max max]

Maximum number of entries in the hashtable

[--dstlimit-htable-gcinterval interval]

Interval between garbage collection runs of the hashtable (in miliseconds). Default is 1000 (1 second).

[--dstlimit-htable-expire time

After which time are idle entries expired from hashtable (in miliseconds)? Default is 10000 (10 seconds).

ecn

--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 ECT (ECN-Capable Transport). You have to specify a number between `0' and `3'.

esp

--espspi [!] spi[:spi]

fuzzy

--lower-limit number

Specifies the lower limit (in packets per second).

--upper-limit number

Specifies the upper limit (in packets per second).

hashlimit

It gives you the ability to express

 '1000 packets per second for every host in 192.168.0.0/16'

 '100 packets per second for every service of 192.168.1.1' with a single iptables rule.

--hashlimit rate

A rate just like the limit match

--hashlimit-burst num

Burst value, just like limit match

--hashlimit-mode destip | destip-destport

Limit per IP or per port

--hashlimit-name foo

The name for the /proc/net/ipt_hashlimit/foo entry

--hashlimit-htable-size num

The number of buckets of the hash table

--hashlimit-htable-max num

Maximum entries in the hash

--hashlimit-htable-expire num

After how many miliseconds do hash entries expire

--hashlimit-htable-gcinterval num

How many miliseconds between garbage collection intervals

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.

icmp

--icmp-type [!] typename

This allows specification of the ICMP type, which can be a numeric ICMP type, or one of the ICMP type names shown by the command

 iptables -p icmp -h

iprange

[!]--src-range ip-ip

Match source IP in the specified range.

[!]--dst-range ip-ip

Match destination IP in the specified range.

ipv4options

--ssrr

To match packets with the flag strict source routing.

--lsrr

To match packets with the flag loose source routing.

--no-srr

To match packets with no flag for source routing.

[!] --rr

To match packets with the RR flag.

[!] --ts

To match packets with the TS flag.

[!] --ra

To match packets with the router-alert option.

[!] --any-opt

To match a packet with at least one IP option, or no IP option at all if ! is chosen.

Examples:

$ iptables -A input -m ipv4options --rr -j DROP

will drop packets with the record-route flag.

$ iptables -A input -m ipv4options --ts -j DROP

will drop packets with the timestamp flag.

length

--length [!] length[:length]

limit

--limit rate

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

--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.

mark

--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).

mport

--source-ports port[,port[,port...]]

Match if the source port is one of the given ports. The flag --sports is a convenient alias for this option.

--destination-ports 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...]]

Match if the both the source and destination ports are equal to each other and to one of the given ports.

multiport

--source-ports [!] 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.

--destination-ports [!] 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.

nth

--every value

Match every `value' packet

[--counter num]

Use internal counter number `num'. Default is `0'.

[--start num]

Initialize the counter at the number `num' insetad of `0'. Most between `0' and `value'-1.

[--packet num]

Match on `num' packet. Most be between `0' and `value'-1.

osf

Original fingerprint table was created by Michal Zalewski <lcamtuf@coredump.cx>.

This module compares some data(WS, MSS, options and it's order, ttl, df and others) from first SYN packet (actually from packets with SYN bit set) with dynamically loaded OS fingerprints.

--log 1/0

If present, OSF will log determined genres even if they don't match desired one.    
0 - log all determined entries, 1 - only first one.

In syslog you find something like this:

ipt_osf: Windows [2000:SP3:Windows XP Pro SP1, 2000 SP3]: 11.22.33.55:4024 -> 11.22.33.44:139

ipt_osf: Unknown: 16384:106:1:48:020405B401010402 44.33.22.11:1239 -> 11.22.33.44:80

--smart

if present, OSF will use some smartness to determine remote OS. OSF will use initial TTL only if source of connection is in our local network.

--netlink

If present, OSF will log all events also through netlink NETLINK_NFLOG groupt 1.

--genre [!] string

Match a OS genre by passive fingerprinting Example:

#iptables -I INPUT -j ACCEPT -p tcp -m osf --genre Linux --log 1 --smart

NOTE: -p tcp is obviously required as it is a TCP match.

Fingerprints can be loaded and read through /proc/sys/net/ipv4/osf file. One can flush all fingerprints with following command:

echo -en FLUSH > /proc/sys/net/ipv4/osf Only one fingerprint per open/write/close.

Fingerprints can be downloaded from http://www.openbsd.org/cgi-bin/cvsweb/src/etc/pf.os

owner

--uid-owner userid

Matches if the packet was created by a process with the given effective user id.

--gid-owner groupid

Matches if the packet was created by a process with the given effective group id.

--pid-owner processid

Matches if the packet was created by a process with the given process id.

--sid-owner sessionid

Matches if the packet was created by a process in the given session group.

--cmd-owner name

Matches if the packet was created by a process with the given command name. (this option is present only if iptables was compiled under a kernel supporting this feature)

NOTE: pid, sid and command matching are broken on SMP

physdev

--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 packets entering the FORWARD, OUTPUT and POSTROUTING chains). If the interface name ends in a "+", then any interface which begins with this name will match. Note that in the nat and mangle OUTPUT chains one cannot match on the bridge output port, however one can in the filter OUTPUT chain. If the packet won't leave by a bridge device or it is yet unknown what the output device will be, then the packet won't match this option, unless

[!] --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.

pkttype

--pkt-type [unicast|broadcast|multicast]

policy

--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.

--strict

Selects whether to match the exact policy or match if any rule of the policy matches the given policy.

--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

psd

--psd-weight-threshold threshold

Total weight of the latest TCP/UDP packets with different destination ports coming from the same host to be treated as port scan sequence.

--psd-delay-threshold delay

Delay (in hundredths of second) for the packets with different destination ports coming from the same host to be treated as possible port scan subsequence.

--psd-lo-ports-weight weight

Weight of the packet with privileged (<=1024) destination port.

--psd-hi-ports-weight weight

Weight of the packet with non-priviliged destination port.

quota

--quota bytes

The quota in bytes. KNOWN BUGS: this does not work on SMP systems.

random

--average percent

Matches the given percentage. If omitted, a probability of 50% is set.

realm

--realm [!]value[/mask]

Matches a given realm number (and optionally mask).

recent

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.

--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).

[!] --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.

[!] --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.

--rttl

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 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 Official website (http://snowman.net/projects/ipt_recent/) also has some examples of usage.

/proc/net/ipt_recent/* are the current lists of addresses and information about each entry of each list.

Each file in /proc/net/ipt_recent/ can be read from to see the current list or written two using the following commands to modify the list:

echo xx.xx.xx.xx > /proc/net/ipt_recent/DEFAULT

to Add to the DEFAULT list

echo -xx.xx.xx.xx > /proc/net/ipt_recent/DEFAULT

to Remove from the DEFAULT list

echo clear > /proc/net/ipt_recent/DEFAULT

to empty the DEFAULT list. 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/ipt_recent/* files

debug=0

Set to 1 to get lots of debugging info

sctp

--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

chunk type available flags
DATA U B E 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

set

--set setname flag[,flag...]

where flags are src and/or dst and there can be no more than six of them. Hence the command

 iptables -A FORWARD -m set --set test src,dst

will match packets, for which (depending on the type of the set) the source address or port number of the packet can be found in the specified set. If there is a binding belonging to the mached set element or there is a default binding for the given set, then the rule will match the packet only if additionally (depending on the type of the set) the destination address or port number of the packet can be found in the set according to the binding.

state

--state state

Where state is a comma separated list of the connection states to match. Possible states are INVALID meaning that the packet could not be identified for some reason which includes running out of memory and ICMP errors which don't correspond to any known connection, ESTABLISHED meaning that the packet is associated with a connection which has seen packets in both directions, NEW meaning that the packet has started a new connection, or otherwise associated with a connection which has not seen packets in both directions, and RELATED meaning that the packet is starting a new connection, but is associated with an existing connection, such as an FTP data transfer, or an ICMP error.

string

--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 from which it starts looking for any matching. If not passed, default is the packet size.

--string pattern

Matches the given pattern. --hex-string pattern Matches the given pattern in hex notation.

tcp

--source-port [!] 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 port:port. If the first port is omitted, "0" is assumed; if the last is omitted, "65535" is assumed. If the second port greater then the first they will be swapped. The flag --sport is a convenient alias for this option.

--destination-port [!] 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 is the flags which we should examine, written as a comma-separated list, and the second argument 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.

--mss value[:value]

Match TCP SYN or SYN/ACK packets with the specified MSS value (or range), which control the maximum packet size for that connection.

tcpmss

[!] --mss value[:value]

Match a given TCP MSS value or range.

time

--timestart value

Match only if it is after `value' (Inclusive, format: HH:MM ; default 00:00).

--timestop value

Match only if it is before `value' (Inclusive, format: HH:MM ; default 23:59).

--days listofdays

Match only if today is one of the given days. (format: Mon,Tue,Wed,Thu,Fri,Sat,Sun ; default everyday)

--datestart date

Match only if it is after `date' (Inclusive, format: YYYY[:MM[:DD[:hh[:mm[:ss]]]]] ; h,m,s start from 0 ; default to 1970)

--datestop date

Match only if it is before `date' (Inclusive, format: YYYY[:MM[:DD[:hh[:mm[:ss]]]]] ; h,m,s start from 0 ; default to 2037)

tos

--tos tos

The argument is either a standard name, (use

 iptables -m tos -h
to see the list), or a numeric value to match.

ttl

--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

Details and examples are in the kernel module source.  

udp

--source-port [!] port[:port]

Source port or port range specification. See the description of the --source-port option of the TCP extension for details.

--destination-port [!] port[:port]

Destination port or port range specification. See the description of the --destination-port option of the TCP extension for details.

unclean

TARGET EXTENSIONS

BALANCE

--to-destination ipaddr-ipaddr

Address range to round-robin over.

CLASSIFY

--set-class MAJOR:MINOR

Set the major and minor class value.

CLUSTERIP

--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.

CONNMARK

--set-mark mark[/mask]

Set connection mark. If a mask is specified then only those bits set in the mask is modified.

--save-mark [--mask mask]

Copy the netfilter packet mark value to the connection mark. If a mask is specified then only those bits are copied.

--restore-mark [--mask mask]

Copy the connection mark value to the packet. If a mask is specified then only those bits are copied. This is only valid in the mangle table.

DNAT

--to-destination ipaddr[-ipaddr][:port-port]

which can specify a single new destination IP address, an inclusive range of IP addresses, and optionally, a port range (which is only valid if the rule also specifies -p tcp or -p udp). If no port range is specified, then the destination port will never 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.

DSCP

--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.

ECN

--ecn-tcp-remove

Remove all ECN bits from the TCP header. Of course, it can only be used in conjunction with -p tcp.

IPMARK

This target is to be used inside the mangle table, in the PREROUTING, POSTROUTING or FORWARD hooks.

--addr src/dst

Use source or destination IP address.

--and-mask mask

Perform bitwise `and' on the IP address and this mask.

--or-mask mask

Perform bitwise `or' on the IP address and this mask. The order of IP address bytes is reversed to meet "human order of bytes": 192.168.0.1 is 0xc0a80001. At first the `and' operation is performed, then `or'.

Examples:

We create a queue for each user, the queue number is adequate to the IP address of the user, e.g.: all packets going to/from 192.168.5.2 are directed to 1:0502 queue, 192.168.5.12 -> 1:050c etc.

We have one classifier rule:

tc filter add dev eth3 parent 1:0 protocol ip fw Earlier we had many rules just like below:

iptables -t mangle -A POSTROUTING -o eth3 -d 192.168.5.2 -j MARK --set-mark 0x10502

iptables -t mangle -A POSTROUTING -o eth3 -d 192.168.5.3 -j MARK --set-mark 0x10503 Using IPMARK target we can replace all the mangle/mark rules with only one:

iptables -t mangle -A POSTROUTING -o eth3 -j IPMARK --addr=dst --and-mask=0xffff --or-mask=0x10000 On the routers with hundreds of users there should be significant load decrease (e.g. twice).

IPV4OPTSSTRIP

The target doesn't take any option, and therefore is extremly easy to use :

# iptables -t mangle -A PREROUTING -j IPV4OPTSSTRIP  

LOG

--log-level level

Level of logging (numeric or see syslog.conf(5)).

--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 packet header.

--log-uid

Log the userid of the process which generated the packet.

MARK

--set-mark mark

MASQUERADE

--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 -p tcp or -p udp.

MIRROR

NETMAP

--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.

NFQUEUE

--queue-num value

This specifies the QUEUE number to use. Valud queue numbers are 0 to 65535. The default value is 0.

It can only be used with Kernel versions 2.6.14 or later, since it requires

the nfnetlink_queue kernel support.

NOTRACK

It can only be used in the

raw table.

REDIRECT

--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 -p tcp or -p udp.

REJECT

--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 (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

ROUTE

--oif ifname

Route the packet through `ifname' network interface

--iif ifname

Change the packet's incoming interface to `ifname'

--gw IP_address

Route the packet via this gateway

--continue

Behave like a non-terminating target and continue traversing the rules. Not valid in combination with `--iif' or `--tee'

--tee

Make a copy of the packet, and route that copy to the given destination. For the original, uncopied packet, behave like a non-terminating target and continue traversing the rules. Not valid in combination with `--iif' or `--continue'

SAME

--to <ipaddr>-<ipaddr>

Addresses to map source to. May be specified more than once for multiple ranges.

--nodst

Don't use the destination-ip in the calculations when selecting the new source-ip

SET

--add-set setname flag[,flag...]

add the address(es)/port(s) of the packet to the sets

--del-set setname flag[,flag...]

delete the address(es)/port(s) of the packet from the sets, where flags are src and/or dst and there can be no more than six of them.

The bindings to follow must previously be defined in order to use

multilevel adding/deleting by the SET target.

SNAT

--to-source ipaddr[-ipaddr][:port-port]

which can specify a single new source IP address, an inclusive range of IP addresses, and optionally, a port range (which is only valid if the rule also specifies -p tcp or -p udp). 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.

TARPIT

This offers similar functionality to LaBrea <http://www.hackbusters.net/LaBrea/> but doesn't require dedicated hardware or IPs. Any TCP port that you would normally DROP or REJECT can instead become a tarpit.

To tarpit connections to TCP port 80 destined for the current machine:

iptables -A INPUT -p tcp -m tcp --dport 80 -j TARPIT To significantly slow down Code Red/Nimda-style scans of unused address space, forward unused ip addresses to a Linux box not acting as a router (e.g. "ip route 10.0.0.0 255.0.0.0 ip.of.linux.box" on a Cisco), enable IP forwarding on the Linux box, and add:

iptables -A FORWARD -p tcp -j TARPIT

iptables -A FORWARD -j DROP

NOTE:

If you use the conntrack module while you are using TARPIT, you should also use the NOTRACK target, or the kernel will unnecessarily allocate resources for each TARPITted connection. To TARPIT incoming connections to the standard IRC port while using conntrack, you could:

iptables -t raw -A PREROUTING -p tcp --dport 6667 -j NOTRACK

iptables -A INPUT -p tcp --dport 6667 -j TARPIT

TCPMSS

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.

 iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN \
             -j TCPMSS --clamp-mss-to-pmtu

--set-mss value

Explicitly set MSS option to specified value.

--clamp-mss-to-pmtu

Automatically clamp MSS value to (path_MTU - 40).

These options are mutually exclusive.

TOS

--set-tos tos

You can use a numeric TOS values, or use

 iptables -j TOS -h

to see the list of valid TOS names.

TRACE

TTL

Setting or incrementing the TTL field can potentially be very dangerous,

so it should be avoided at any cost.

Don't ever set or increment the value on packets that leave your local network!

mangle table.

--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.

ULOG

--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).

XOR

--key string

Set key to "string"

--block-size

Set block size

DIAGNOSTICS

BUGS

COMPATIBILITY WITH IPCHAINS

The other main difference is that -i refers to the input interface; -o refers to the output interface, and both are available for packets entering the FORWARD chain.

iptables is a pure packet filter when using the default `filter' table, with optional extension modules. This should simplify much of the previous confusion over the combination of IP masquerading and packet filtering seen previously. So the following options are handled differently:

 -j MASQ
 -M -S
 -M -L

SEE ALSO

AUTHORS

Marc Boucher made Rusty abandon ipnatctl by lobbying for a generic packet selection framework in iptables, then wrote the mangle table, the owner match, the mark stuff, and ran around doing cool stuff everywhere.

James Morris wrote the TOS target, and tos match.

Jozsef Kadlecsik wrote the REJECT target.

Harald Welte wrote the ULOG and NFQUEUE target, the new libiptc, as well as the TTL, DSCP, ECN matches and targets.

The Netfilter Core Team is: Marc Boucher, Martin Josefsson, Jozsef Kadlecsik, Patrick McHardy, James Morris, Harald Welte and Rusty Russell.

Man page originally written by Herve Eychenne <rv@wallfire.org>.

Index

NAME

SYNOPSIS

DESCRIPTION

TARGETS

TABLES

OPTIONS

COMMANDS

PARAMETERS

OTHER OPTIONS

MATCH EXTENSIONS

account

addrtype

ah

childlevel

comment

condition

connbytes

connlimit

connmark

connrate

conntrack

dccp

dscp

dstlimit

ecn

esp

fuzzy

hashlimit

helper

icmp

iprange

ipv4options

length

limit

mac

mark

mport

multiport

nth

osf

owner

physdev

pkttype

policy

psd

quota

random

realm

recent

sctp

set

state

string

tcp

tcpmss

time

tos

ttl

u32

udp

unclean

TARGET EXTENSIONS

BALANCE

CLASSIFY

CLUSTERIP

CONNMARK

DNAT

DSCP

ECN

IPMARK

IPV4OPTSSTRIP

LOG

MARK

MASQUERADE

MIRROR

NETMAP

NFQUEUE

NOTRACK

REDIRECT

REJECT

ROUTE

SAME

SET

SNAT

TARPIT

TCPMSS

TOS

TRACE

TTL

ULOG

XOR

DIAGNOSTICS

BUGS

COMPATIBILITY WITH IPCHAINS

SEE ALSO

AUTHORS

Партнёры:

Хостинг: