-A

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

-C

Check whether a rule matching the specification does exist in the selected chain. This command uses the same logic as -D tofind a matching entry, but does not alter the existing iptables configuration and uses its exit code to indicate success orfailure.

-D

--delete chain rule-specification

-I

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 areinserted at the head of the chain. This is also the default if no rule number is specified.

-R

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

-L

List all rules in the selected chain. If no chain is selected, all chains are listed. Like every other iptables command, itapplies to the specified table (filter is the default), so NAT rules get listed byiptables -t nat -n -LPlease note that it is often used with the -n option, in order to avoid long reverse DNS lookups. It is legal to specify the

-S

Print all rules in the selected chain. If no chain is selected, all chains are printed like iptables-save. Like every otheriptables command, it applies to the specified table (filter is the default).

-F

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

-Z

Zero the packet and byte counters in all chains, or only the given chain, or only the given rule in a chain. It is legal tospecify the -L, --list (list) option as well, to see the counters immediately before they are cleared. (See above.)

-N

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

-X

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

-P

Set the policy for the built-in (non-user-defined) chain to the given target. The policy target must be either ACCEPT orDROP.

-E

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

-h

PARAMETERSThe following parameters make up a rule specification (as used in the add, delete, insert, replace and append commands).

-4

This option has no effect in iptables and iptables-restore. If a rule using the -4 option is inserted with (and only with)ip6tables-restore, it will be silently ignored. Any other uses will throw an error. This option allows IPv4 and IPv6 rules ina single rule file for use with both iptables-restore and ip6tables-restore.

-6

If a rule using the -6 option is inserted with (and only with) iptables-restore, it will be silently ignored. Any other useswill throw an error. This option allows IPv4 and IPv6 rules in a single rule file for use with both iptables-restore andip6tables-restore. This option has no effect in ip6tables and ip6tables-restore.[!] -p, --protocol protocolThe protocol of the rule or of the packet to check. The specified protocol can be one of tcp, udp, udplite, icmp, icmpv6,esp,ah, sctp, mh or the special keyword "all", or it can be a numeric value, representing one of these protocols or a differentone. A protocol name from /etc/protocols is also allowed. A "!" argument before the protocol inverts the test. The numberzero is equivalent to all. "all" will match with all protocols and is taken as default when this option is omitted. Notethat, in ip6tables, IPv6 extension headers except esp are not allowed. esp and ipv6-nonext can be used with Kernel version2.6.11 or later. The number zero is equivalent to all, which means that you cannot test the protocol field for the value 0directly. To match on a HBH header, even if it were the last, you cannot use -p 0, but always need -m hbh.[!] -s, --source address[/mask][,...]Source specification. Address can be either a network name, a hostname, a network IP address (with /mask), or a plain IPaddress. Hostnames will be resolved once only, before the rule is submitted to the kernel. Please note that specifying anyname to be resolved with a remote query such as DNS is a really bad idea. The mask can be either an ipv4 network mask (foriptables) or a plain number, specifying the number of 1's at the left side of the network mask. Thus, an iptables mask of 24is equivalent to 255.255.255.0. A "!" argument before the address specification inverts the sense of the address. The flag

--dst

is an alias for this option.

-m

Specifies a match to use, that is, an extension module that tests for a specific property. The set of matches make up the con‐dition under which a target is invoked. Matches are evaluated first to last as specified on the command line and work inshort-circuit fashion, i.e. if one extension yields false, evaluation will stop.

-j

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, oran extension (see EXTENSIONS below). If this option is omitted in a rule (and -g is not used), then matching the rule willhave no effect on the packet's fate, but the counters on the rule will be incremented.

-g

This specifies that the processing should continue in a user specified chain. Unlike the --jump option return will not con‐tinue processing in this chain but instead in the chain that called us via --jump.[!] -i, --in-interface nameName 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 anyinterface which begins with this name will match. If this option is omitted, any interface name will match.[!] -o, --out-interface nameName 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 anyinterface which begins with this name will match. If this option is omitted, any interface name will match.[!] -f, --fragmentThis means that the rule only refers to second and further IPv4 fragments of fragmented packets. Since there is no way totell the source or destination ports of such a packet (or ICMP type), such a packet will not match any rules which specifythem. When the "!" argument precedes the "-f" flag, the rule will only match head fragments, or unfragmented packets. Thisoption is IPv4 specific, it is not available in ip6tables.

-c

This enables the administrator to initialize the packet and byte counters of a rule (during INSERT, APPEND, REPLACE opera‐tions).OTHER OPTIONSThe following additional options can be specified:

-v

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 multipli‐ers respectively (but see the -x flag to change this). For appending, insertion, deletion and replacement, this causesdetailed information on the rule or rules to be printed. -v may be specified multiple times to possibly emit more detaileddebug statements.

-w

Wait for the xtables lock. To prevent multiple instances of the program from running concurrently, an attempt will be made toobtain an exclusive lock at launch. By default, the program will exit if the lock cannot be obtained. This option will makethe program wait (indefinitely or for optional seconds) until the exclusive lock can be obtained.

-W

Interval to wait per each iteration. When running latency sensitive applications, waiting for the xtables lock for extendeddurations may not be acceptable. This option will make each iteration take the amount of time specified. The default intervalis 1 second. This option only works with -w.

-n

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

-x

Expand numbers. Display the exact value of the packet and byte counters, instead of only the rounded number in K's (multiplesof 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

When adding or inserting rules into a chain, use command to load any necessary modules (targets, match extensions, etc).MATCH AND TARGET EXTENSIONSiptables can use extended packet matching and target modules. A list of these is available in the iptables-extensions(8) manpage.DIAGNOSTICSVarious error messages are printed to standard error. The exit code is 0 for correct functioning. Errors which appear to be causedby invalid or abused command line parameters cause an exit code of 2, and other errors cause an exit code of 1.BUGSBugs? What's this? ;-) Well, you might want to have a look at http://bugzilla.netfilter.org/COMPATIBILITY WITH IPCHAINSThis iptables is very similar to ipchains by Rusty Russell. The main difference is that the chains INPUT and OUTPUT are only tra‐versed for packets coming into the local host and originating from the local host respectively. Hence every packet only passesthrough one of the three chains (except loopback traffic, which involves both INPUT and OUTPUT chains); previously a forwarded packetwould pass through all three.The other main difference is that -i refers to the input interface; -o refers to the output interface, and both are available forpackets entering the FORWARD chain.The various forms of NAT have been separated out; iptables is a pure packet filter when using the default `filter' table, withoptional extension modules. This should simplify much of the previous confusion over the combination of IP masquerading and packetfiltering seen previously. So the following options are handled differently:

-M

There are several other changes in iptables.