ip6tables
IPv6 packet filter administration
see also :
ip6tables-save - ip6tables-restore - iptables - iptables-save - iptables-restore
Synopsis
ip6tables
[-t table]
{-A|-C|-D} 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] -S [chain
[rulenum]]
ip6tables
[-t table]
{-F|-L|-Z}
[chain [rulenum]] [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
add an example, a script, a trick and tips
examples
source
service ip6tables stop
chkconfig iptables off
chkconfig ip6tables off
source
source /filter/fw6.conf
ip6tables -F
ip6tables -X
ip6tables -P INPUT ACCEPT
ip6tables -P OUTPUT ACCEPT
ip6tables -P FORWARD ACCEPT
source
sudo /sbin/chkconfig ip6tables off
sudo /sbin/service iptables stop
sudo /sbin/service ip6tables stop
description
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.
options
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.
-C,
--check chain
rule-specification
Check whether a rule matching
the specification does exist in the selected chain. This
command uses the same logic as -D to find a
matching entry, but does not alter the existing iptables
configuration and uses its exit code to indicate success or
failure.
-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. Like
every other ip6tables command, it applies to the specified
table (filter is the default).
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
-S,
--list-rules [chain]
Print all rules in the selected
chain. If no chain is selected, all chains are printed like
ip6tables-save. Like every other ip6tables command, it
applies to the specified table (filter is the default).
-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
[rulenum]]
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 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.
-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.
-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, udplite, icmpv6,
esp, mh or the special keyword
"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. "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 be a hostname, a network IP
address (with /mask), or a plain IP address.
Names will be resolved once only, before the rule is
submitted to the kernel. Please note that specifying any
name to be resolved with a remote query such as DNS is a
really bad idea. (Resolving network names is not supported
at this time.) The mask is a plain number, specifying
the number of 1’s at the left side of the network
mask. A "!" argument before the address
specification inverts the sense of the address. The flag
--src is an alias for this option.
Multiple addresses can be specified, but this will expand
to multiple rules (when adding with -A), or will
cause multiple rules to be deleted (with -D).
[!] -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.
-c,
--set-counters packets
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.
-v may be specified multiple times to possibly
emit more detailed debug statements.
-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).
compatibility with ipchains
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.
diagnostics
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.
match extensions
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.
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.
cluster
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
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
comment
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"
connbytes
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 ...
connlimit
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.
--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
connmark
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).
conntrack
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
meaning that the packet is associated with no known connection
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
ESTABLISHED
meaning that the packet is associated with a connection which has
seen packets in both directions,
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.
UNTRACKED
meaning that the packet is not tracked at all, which happens if
you use the NOTRACK target in 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
[!] --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.
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
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.
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 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.
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 fragment.
hashlimit
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" (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 as a number, with an optional time quantum suffix;
the default is 3/hour.
--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.
--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.
Examples:
matching on source host
"1000 packets per second for every host in 192.168.0.0/16" =>
-s 192.168.0.0/16 --hashlimit-mode srcip --hashlimit-upto
1000/sec
matching on source port
"100 packets per second for every service of 192.168.1.1" =>
-s 192.168.1.1 --hashlimit-mode srcport --hashlimit-upto 100/sec
matching on subnet
"10000 packets per minute for every /28 subnet (groups of 8
addresses) in 10.0.0.0/8" => -s 10.0.0.8 --hashlimit-mask 28
--hashlimit-upto 10000/min
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.
helper
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.
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.
icmp6
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
iprange
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.
ipv6header
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
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.
ipvs
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
length
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]
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. 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
[!] --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).
mh
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 ipv6-mh -h
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. It can only be used in conjunction with -p tcp or
-p udp.
[!] --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.
owner
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.
[!] --socket-exists
Matches if the packet is associated with a socket.
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
if it is yet unknown what the output device will be, then the
packet won’t match this option, unless ’!’ is used.
[!] --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
This module matches the link-layer packet type.
[!] --pkt-type
{unicast|broadcast|multicast}
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. --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.
quota
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.
rateest
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
recent
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.
[!] --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 reap
This option can only be used in conjunction with
--seconds. When used, this will cause entries older then
’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
Steve’s ipt_recent website
(http://snowman.net/projects/ipt_recent/) also has some examples
of usage.
/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.
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.
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 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
set
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.
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. As
standard kernels do not ship this currently, the ipset or
Xtables-addons package needs to be installed.
socket
This matches if an open socket can be found by doing a socket
lookup on the packet.
--transparent
Ignore non-transparent sockets.
state
This module, when combined with connection tracking, 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. 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. UNTRACKED meaning that the packet is not
tracked at all, which happens if you use the NOTRACK target in
raw table.
statistic
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.
string
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.
tcp
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. If the first port is greater than
the second one they will be swapped. 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.
tcpmss
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.
time
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.).
--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.)
tos
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.
u32
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.
udp
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.
tables
There are currently three independent tables (which tables are
present at any time depends on the kernel configuration options
and which modules are present).
-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).
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)
security:
This table is used for Mandatory Access Control (MAC) networking
rules, such as those enabled by the SECMARK and
CONNSECMARK targets. Mandatory Access Control is
implemented by Linux Security Modules such as SELinux. The
security table is called after the filter table, allowing any
Discretionary Access Control (DAC) rules in the filter table to
take effect before MAC rules. This table provides the following
built-in chains: INPUT (for packets coming into the box
itself), OUTPUT (for altering locally-generated packets
before routing), and FORWARD (for altering packets being
routed through the box).
targets
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.
target extensions
ip6tables can use extended target modules: the following are
included in the standard distribution.
AUDIT
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.
Example:
iptables -N AUDIT_DROP
iptables -A AUDIT_DROP -j AUDIT --type drop
iptables -A AUDIT_DROP -j DROP
CHECKSUM
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.
CLASSIFY
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.
CONNMARK
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.
CONNSECMARK
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.
CT
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 id
Assign this packet to zone id and only have lookups done
in that zone. By default, packets have zone 0.
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.
IDLETIMER
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.
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 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.)
NFLOG
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
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.
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. It can only be used with
Kernel versions 2.6.14 or later, since it requires the
nfnetlink_queue kernel support. 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 is silently bypassed instead.
The packet will move on to the next rule.
NOTRACK
This target disables connection tracking for all packets matching
that rule.
It can only be used in the raw table.
RATEEST
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.
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 or 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 later.
SECMARK
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
SET
This modules 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 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 specifications and
there can be no more than six of them.
--timeout value
when adding entry, the timeout value to use instead of the
default one from the set definition
--exist
when adding entry if it already exists, reset the timeout value
to the specified one or to the default from the set definition
Use of -j SET requires that ipset kernel support is provided. As
standard kernels do not ship this currently, the ipset or
Xtables-addons package needs to be installed.
TCPMSS
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.
TCPOPTSTRIP
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.
TEE
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 0.0.0.0 (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
TOS
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 (or later) and 2.6.33.15
(or later), 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.
TPROXY
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.)
TRACE
This target marks packes so that the kernel will log every rule
which match the packets as those traverse the tables, chains,
rules.
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.
It can only be used in the raw table.
version
This manual page applies to ip6tables @PACKAGE_VERSION@.
bugs
Bugs?
What’s this? ;-) Well... the counters are not reliable
on sparc64.
see also
ip6tables-save ,
ip6tables-restore , iptables ,
iptables-save ,
iptables-restore , libipq.
The
packet-filtering-HOWTO details iptables usage for packet
filtering, 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/.
authors
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, as well
as TTL match+target and libipulog.
The Netfilter
Core Team is: Marc Boucher, Martin Josefsson, Yasuyuki
Kozakai, Jozsef Kadlecsik, Patrick McHardy, James Morris,
Pablo Neira Ayuso, Harald Welte and Rusty Russell.
ip6tables man
page created by Andras Kis-Szabo, based on iptables man page
written by Herve Eychenne <rv[:at:]wallfire[:dot:]org>.