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CentOS 5.6 |
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ip6tables(8) |
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ip6tables − IPv6 packet filter administration
ip6tables
[-t table] -[AD] chain rule-specification [options]
ip6tables [-t table] -I chain [rulenum]
rule-specification [options]
ip6tables [-t table] -R chain rulenum rule-specification
[options]
ip6tables [-t table] -D chain rulenum [options]
ip6tables [-t table] -[LFZ] [chain] [options]
ip6tables [-t table] -N chain
ip6tables [-t table] -X [chain]
ip6tables [-t table] -P chain target [options]
ip6tables [-t table] -E old-chain-name
new-chain-name
Ip6tables is used to set up, maintain, and inspect the tables of IPv6 packet filter rules in the Linux kernel. Several different tables may be defined. Each table contains a number of built-in chains and may also contain user-defined chains.
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.
A firewall rule specifies criteria for a packet, and a target. If the packet does not match, the next rule in the chain is the examined; if it does match, then the next rule is specified by the value of the target, which can be the name of a user-defined chain or one of the special values ACCEPT, DROP, QUEUE, or RETURN.
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.
There are
currently two independent tables (which tables are present
at any time depends on the kernel configuration options and
which modules are present), as nat table has not been
implemented yet.
-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 coming into the box itself), FORWARD (for packets being routed through the box), and OUTPUT (for locally-generated packets).
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 nf_conntrack, or any other IP6 tables. It provides the following built-in chains: PREROUTING (for packets arriving via any network interface) OUTPUT (for packets generated by local processes)
The options that are recognized by ip6tables can be divided into several different groups.
COMMANDS
These options specify the specific action to perform. Only
one of them can be specified on the command line unless
otherwise specified below. For all the long versions of the
command and option names, you need to use only enough
letters to ensure that ip6tables can differentiate it
from all other options.
-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
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 mangle rules get listed by
ip6tables -t mangle -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
ip6tables -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. 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
The following parameters make up a rule specification (as
used in the add, delete, insert, replace and append
commands).
-p, --protocol [!] protocol
The protocol of the rule or of the packet to check. The specified protocol can be one of tcp, udp, icmpv6, esp, 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. But IPv6 extension headers except esp are not allowed. esp, and ipv6-nonext can be used with Kernel version 2.6.11 or later. 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 hostname (please note that specifying any name to be resolved with a remote query such as DNS is a really bad idea), a network IPv6 address (with /mask), or a plain IPv6 address. (the network name isn’t supported now). 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 64 is equivalent to ffff:ffff:ffff:ffff:0000:0000:0000:0000. 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, then matching the rule will have no effect on the packet’s fate, but the counters on the rule will be incremented.
-i, --in-interface [!] name
Name of an interface via which a packet is going to be 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 and OUTPUT 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.
-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
The following additional options can be specified:
-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).
ip6tables can use extended packet matching modules. These are loaded in two ways: implicitly, when -p or --protocol is specified, or 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 following are included in the base package, and most of these can be preceded by a ! to invert the sense of the match.
ah
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.
condition
This matches if a specific /proc filename is ’0’
or ’1’.
--condition [!] filename
Match on boolean value stored in /proc/net/ip6t_condition/filename file
dst
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.
esp
This module matches the SPIs in ESP header of IPsec packets.
--espspi [!] spi[:spi]
eui64
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 Ehternet 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.
frag
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 fragement.
fuzzy
This module matches a rate limit based on a fuzzy logic
controller [FLC]
--lower-limit number
Specifies the lower limit (in packets per second).
--upper-limit number
Specifies the upper limit (in packets per second).
hbh
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.
hl
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.
icmpv6
This extension is loaded 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
ipv6header
This module matches IPv6 extension headers and/or upper
layer header.
--header [!] header[,header...]
Matches the packet which EXACTLY includes all specified headers. The headers encapsulated with ESP header are out of scope. header 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, or proto which matches any upper layer protocol header. A protocol name from /etc/protocols and numeric value also allowed. The number 255 is equivalent to proto.
[--soft]
Matches if the packet includes all specified headers with --header, AT LEAST.
length
This module matches the length of the IPv6 payload in
octets, or range of it. IPv6 header itself isn’t
counted.
--length [!] length[:length]
limit
This module matches at a limited rate using a token bucket
filter. A rule using this extension will match until this
limit is reached (unless the ’!’ flag is used).
It can be used in combination with the LOG target to
give limited logging, for example.
--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
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).
multiport
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, but range isn’t supported now. It
can only be used in conjunction with -p tcp or -p
udp.
--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 the both the source and destination ports are equal to each other and to one of the given ports.
nth
This module matches every ’n’th packet
--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.
owner
This module attempts to match various characteristics of the
packet creator, for locally-generated packets. It is only
valid in the OUTPUT chain, and even this some packets
(such as ICMPv6 ping responses) may have no owner, and hence
never match. This is regarded as experimental.
--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.
NOTE: pid, sid and command matching are broken on SMP
physdev
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 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.
policy
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.
--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 |
random
This module randomly matches a certain percentage of all
packets.
--average percent
Matches the given percentage. If omitted, a probability of 50% is set.
rt
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.
tcp
These extensions are loaded if ’--protocol tcp’
is specified. It provides the following options:
--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
ip6tables -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 and RST 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 SYN. If the "!" flag precedes the "--syn", the sense of the option is inverted.
--tcp-option [!] number
Match if TCP option set.
udp
These extensions are loaded if ’--protocol udp’
is specified. It provides the following options:
--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.
ip6tables can use extended target modules: the following are included in the standard distribution.
DSCP
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.
HL
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.
LOG
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 IPv6
IPv6-header fields) via the kernel log (where it can be read
with dmesg or syslogd(8)). 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 (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 IPv6 packet header.
--log-uid
Log the userid of the process which generated the packet.
MARK
This is used to set the netfilter mark value associated with
the packet. It is only valid in the mangle table.
--set-mark mark
NFQUEUE
This target is an extension of the QUEUE target. As opposed
to QUEUE, it allows you to put a packet into any specific
queue, identified by its 16-bit queue number.
--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.
REJECT
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
icmp6-port-unreachable
port-unreach
which return the appropriate ICMPv6 error message
(port-unreach 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 latter.
TRACE
This target has no options. It just turns on packet
tracing for all packets that match this rule.
Various error messages are printed to standard error. The exit code is 0 for correct functioning. Errors which appear to be caused by invalid or abused command line parameters cause an exit code of 2, and other errors cause an exit code of 1.
Bugs? What’s this? ;-) Well... the counters are not reliable on sparc64.
This ip6tables is very similar to ipchains by Rusty Russell. The main difference is that the chains INPUT and OUTPUT are only traversed for packets coming into the local host and originating from the local host respectively. Hence every packet only passes through one of the three chains (except loopback traffic, which involves both INPUT and OUTPUT chains); previously a forwarded packet would 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 for packets entering the FORWARD chain. There are several other changes in ip6tables.
ip6tables-save(8), ip6tables-restore(8), iptables(8), iptables-save(8), iptables-restore(8), libipq(3).
The
packet-filtering-HOWTO details iptables usage for packet
filtering, the NAT-HOWTO details NAT, the
netfilter-extensions-HOWTO details the extensions that are
not in the standard distribution, and the
netfilter-hacking-HOWTO details the netfilter internals.
See http://www.netfilter.org/.
Rusty Russell wrote iptables, in early consultation with Michael Neuling.
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, aswell as TTL match+target and libipulog.
The Netfilter Core Team is: Marc Boucher, Martin Josefsson, Jozsef Kadlecsik, James Morris, Harald Welte and Rusty Russell.
ip6tables man page created by Andras Kis-Szabo, based on iptables man page written by Herve Eychenne <rv@wallfire.org>.
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ip6tables(8) | |