iptables can use extended packet matching modules with the -m or
--match options, followed by the matching module name; after
these, various extra command line options become available,
depending on the specific module. You can specify multiple
extended match modules in one line, and you can use the -h or
--help options after the module has been specified to receive
help specific to that module. The extended match modules are
evaluated in the order they are specified in the rule.
If the -p or --protocol was specified and if and only if an
unknown option is encountered, iptables will try load a match
module of the same name as the protocol, to try making the option
available.
addrtype
This module matches packets based on their address type. Address
types are used within the kernel networking stack and categorize
addresses into various groups. The exact definition of that
group depends on the specific layer three protocol.
The following address types are possible:
UNSPEC an unspecified address (i.e. 0.0.0.0)
UNICAST
an unicast address
LOCAL a local address
BROADCAST
a broadcast address
ANYCAST
an anycast packet
MULTICAST
a multicast address
BLACKHOLE
a blackhole address
UNREACHABLE
an unreachable address
PROHIBIT
a prohibited address
THROW FIXME
NAT FIXME
XRESOLVE
[!] --src-type type
Matches if the source address is of given type
[!] --dst-type type
Matches if the destination address is of given type
--limit-iface-in
The address type checking can be limited to the interface
the packet is coming in. This option is only valid in the
PREROUTING, INPUT and FORWARD chains. It cannot be
specified with the --limit-iface-out option.
--limit-iface-out
The address type checking can be limited to the interface
the packet is going out. This option is only valid in the
POSTROUTING, OUTPUT and FORWARD chains. It cannot be
specified with the --limit-iface-in option.
ah (IPv6-specific)
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.
ah (IPv4-specific)
This module matches the SPIs in Authentication header of IPsec
packets.
[!] --ahspi spi[:spi]
bpf
Match using Linux Socket Filter. Expects a path to an eBPF object
or a cBPF program in decimal format.
--object-pinned path
Pass a path to a pinned eBPF object.
Applications load eBPF programs into the kernel with the bpf()
system call and BPF_PROG_LOAD command and can pin them in a
virtual filesystem with BPF_OBJ_PIN. To use a pinned object in
iptables, mount the bpf filesystem using
mount -t bpf bpf ${BPF_MOUNT}
then insert the filter in iptables by path:
iptables -A OUTPUT -m bpf --object-pinned
${BPF_MOUNT}/{PINNED_PATH} -j ACCEPT
--bytecode code
Pass the BPF byte code format as generated by the
nfbpf_compile utility.
The code format is similar to the output of the tcpdump -ddd
command: one line that stores the number of instructions,
followed by one line for each instruction. Instruction lines
follow the pattern 'u16 u8 u8 u32' in decimal notation. Fields
encode the operation, jump offset if true, jump offset if false
and generic multiuse field 'K'. Comments are not supported.
For example, to read only packets matching 'ip proto 6', insert
the following, without the comments or trailing whitespace:
4 # number of instructions
48 0 0 9 # load byte ip->proto
21 0 1 6 # jump equal IPPROTO_TCP
6 0 0 1 # return pass (non-zero)
6 0 0 0 # return fail (zero)
You can pass this filter to the bpf match with the following
command:
iptables -A OUTPUT -m bpf --bytecode '4,48 0 0 9,21 0 1
6,6 0 0 1,6 0 0 0' -j ACCEPT
Or instead, you can invoke the nfbpf_compile utility.
iptables -A OUTPUT -m bpf --bytecode "`nfbpf_compile RAW
'ip proto 6'`" -j ACCEPT
Or use tcpdump -ddd. In that case, generate BPF targeting a
device with the same data link type as the xtables match.
Iptables passes packets from the network layer up, without mac
layer. Select a device with data link type RAW, such as a tun
device:
ip tuntap add tun0 mode tun
ip link set tun0 up
tcpdump -ddd -i tun0 ip proto 6
See tcpdump -L -i $dev for a list of known data link types for a
given device.
You may want to learn more about BPF from FreeBSD's bpf(4)
manpage.
cgroup
[!] --path path
Match cgroup2 membership.
Each socket is associated with the v2 cgroup of the
creating process. This matches packets coming from or
going to all sockets in the sub-hierarchy of the specified
path. The path should be relative to the root of the
cgroup2 hierarchy.
[!] --cgroup classid
Match cgroup net_cls classid.
classid is the marker set through the cgroup net_cls
controller. This option and --path can't be used
together.
Example:
iptables -A OUTPUT -p tcp --sport 80 -m cgroup ! --path
service/http-server -j DROP
iptables -A OUTPUT -p tcp --sport 80 -m cgroup ! --cgroup
1 -j DROP
IMPORTANT: when being used in the INPUT chain, the cgroup matcher
is currently only of limited functionality, meaning it will only
match on packets that are processed for local sockets through
early socket demuxing. Therefore, general usage on the INPUT
chain is not advised unless the implications are well understood.
Available since Linux 3.14.
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
NOTE: the arptables commands above use mainstream syntax. If you
are using arptables-jf included in some RedHat, CentOS and Fedora
versions, you will hit syntax errors. Therefore, you'll have to
adapt these to the arptables-jf syntax to get them working.
In the case of TCP connections, pickup facility has to be
disabled to avoid marking TCP ACK packets coming in the reply
direction as valid.
echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose
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. This is the default
if --connlimit-daddr is not specified.
--connlimit-daddr
Apply the limit onto the destination group.
Examples:
# allow 2 telnet connections per client host
iptables -A INPUT -p tcp --syn --dport 23 -m connlimit
--connlimit-above 2 -j REJECT
# you can also match the other way around:
iptables -A INPUT -p tcp --syn --dport 23 -m connlimit
--connlimit-upto 2 -j ACCEPT
# limit the number of parallel HTTP requests to 16 per class C
sized source network (24 bit netmask)
iptables -p tcp --syn --dport 80 -m connlimit
--connlimit-above 16 --connlimit-mask 24 -j REJECT
# limit the number of parallel HTTP requests to 16 for the link
local network
(ipv6) ip6tables -p tcp --syn --dport 80 -s fe80::/64 -m
connlimit --connlimit-above 16 --connlimit-mask 64 -j
REJECT
# Limit the number of connections to a particular host:
ip6tables -p tcp --syn --dport 49152:65535 -d 2001:db8::1
-m connlimit --connlimit-above 100 -j REJECT
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
The packet is associated with no known connection.
NEW The packet has started a new connection or otherwise
associated with a connection which has not seen packets in
both directions.
ESTABLISHED
The packet is associated with a connection which has seen
packets in both directions.
RELATED
The packet is starting a new connection, but is associated
with an existing connection, such as an FTP data transfer
or an ICMP error.
UNTRACKED
The packet is not tracked at all, which happens if you
explicitly untrack it by using -j CT --notrack in the raw
table.
SNAT A virtual state, matching if the original source address
differs from the reply destination.
DNAT A virtual state, matching if the original destination
differs from the reply source.
Statuses for --ctstatus:
NONE None of the below.
EXPECTED
This is an expected connection (i.e. a conntrack helper
set it up).
SEEN_REPLY
Conntrack has seen packets in both directions.
ASSURED
Conntrack entry should never be early-expired.
CONFIRMED
Connection is confirmed: originating packet has left box.
cpu
[!] --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 DCCP option set.
devgroup
Match device group of a packets incoming/outgoing interface.
[!] --src-group name
Match device group of incoming device
[!] --dst-group name
Match device group of outgoing device
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 (IPv6-specific)
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.
ecn
This allows you to match the ECN bits of the IPv4/IPv6 and TCP
header. ECN is the Explicit Congestion Notification mechanism as
specified in RFC3168
[!] --ecn-tcp-cwr
This matches if the TCP ECN CWR (Congestion Window
Received) bit is set.
[!] --ecn-tcp-ece
This matches if the TCP ECN ECE (ECN Echo) bit is set.
[!] --ecn-ip-ect num
This matches a particular IPv4/IPv6 ECT (ECN-Capable
Transport). You have to specify a number between `0' and
`3'.
esp
This module matches the SPIs in ESP header of IPsec packets.
[!] --espspi spi[:spi]
eui64 (IPv6-specific)
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 (IPv6-specific)
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" or "N bytes per
seconds" (see below for some examples).
A hash limit option (--hashlimit-upto, --hashlimit-above) and
--hashlimit-name are required.
--hashlimit-upto amount[/second|/minute|/hour|/day]
Match if the rate is below or equal to amount/quantum. It
is specified either as a number, with an optional time
quantum suffix (the default is 3/hour), or as
amountb/second (number of bytes per second).
--hashlimit-above amount[/second|/minute|/hour|/day]
Match if the rate is above amount/quantum.
--hashlimit-burst amount
Maximum initial number of packets to match: this number
gets recharged by one every time the limit specified above
is not reached, up to this number; the default is 5. When
byte-based rate matching is requested, this option
specifies the amount of bytes that can exceed the given
rate. This option should be used with caution -- if the
entry expires, the burst value is reset too.
--hashlimit-mode {srcip|srcport|dstip|dstport},...
A comma-separated list of objects to take into
consideration. If no --hashlimit-mode option is given,
hashlimit acts like limit, but at the expensive of doing
the hash housekeeping.
--hashlimit-srcmask prefix
When --hashlimit-mode srcip is used, all source addresses
encountered will be grouped according to the given prefix
length and the so-created subnet will be subject to
hashlimit. prefix must be between (inclusive) 0 and 32.
Note that --hashlimit-srcmask 0 is basically doing the
same thing as not specifying srcip for --hashlimit-mode,
but is technically more expensive.
--hashlimit-dstmask prefix
Like --hashlimit-srcmask, but for destination addresses.
--hashlimit-name foo
The name for the /proc/net/ipt_hashlimit/foo entry.
--hashlimit-htable-size buckets
The number of buckets of the hash table
--hashlimit-htable-max entries
Maximum entries in the hash.
--hashlimit-htable-expire msec
After how many milliseconds do hash entries expire.
--hashlimit-htable-gcinterval msec
How many milliseconds between garbage collection
intervals.
--hashlimit-rate-match
Classify the flow instead of rate-limiting it. This acts
like a true/false match on whether the rate is above/below
a certain number
--hashlimit-rate-interval sec
Can be used with --hashlimit-rate-match to specify the
interval at which the rate should be sampled
Examples:
matching on source host
"1000 packets per second for every host in 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 10.0.0.0/8
--hashlimit-mask 28 --hashlimit-upto 10000/min
matching bytes per second
"flows exceeding 512kbyte/s" => --hashlimit-mode
srcip,dstip,srcport,dstport --hashlimit-above 512kb/s
matching bytes per second
"hosts that exceed 512kbyte/s, but permit up to 1Megabytes
without matching" --hashlimit-mode dstip --hashlimit-above
512kb/s --hashlimit-burst 1mb
hbh (IPv6-specific)
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 (IPv6-specific)
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.
icmp (IPv4-specific)
This extension can be used if `--protocol icmp' is specified. It
provides the following option:
[!] --icmp-type {type[/code]|typename}
This allows specification of the ICMP type, which can be a
numeric ICMP type, type/code pair, or one of the ICMP type
names shown by the command
iptables -p icmp -h
icmp6 (IPv6-specific)
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 (IPv6-specific)
This module matches IPv6 extension headers and/or upper layer
header.
--soft Matches if the packet includes any of the headers
specified with --header.
[!] --header header[,header...]
Matches the packet which EXACTLY includes all specified
headers. The headers encapsulated with ESP header are out
of scope. Possible header types can be:
hop|hop-by-hop
Hop-by-Hop Options header
dst Destination Options header
route Routing header
frag Fragment header
auth Authentication header
esp Encapsulating Security Payload header
none No Next header which matches 59 in the 'Next Header field'
of IPv6 header or any IPv6 extension headers
prot which matches any upper layer protocol header. A protocol
name from /etc/protocols and numeric value also allowed.
The number 255 is equivalent to prot.
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 (IPv6-specific)
This extension is loaded if `--protocol ipv6-mh' or `--protocol
mh' is specified. It provides the following option:
[!] --mh-type type[:type]
This allows specification of the Mobility Header(MH) type,
which can be a numeric MH type, type or one of the MH type
names shown by the command
ip6tables -p mh -h
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 one of the
following protocols: tcp, udp, udplite, dccp and sctp.
[!] --source-ports,--sports port[,port|,port:port]...
Match if the source port is one of the given ports. The
flag --sports is a convenient alias for this option.
Multiple ports or port ranges are separated using a comma,
and a port range is specified using a colon.
53,1024:65535 would therefore match ports 53 and all from
1024 through 65535.
[!] --destination-ports,--dports port[,port|,port:port]...
Match if the destination port is one of the given ports.
The flag --dports is a convenient alias for this option.
[!] --ports port[,port|,port:port]...
Match if either the source or destination ports are equal
to one of the given ports.
nfacct
The nfacct match provides the extended accounting infrastructure
for iptables. You have to use this match together with the
standalone user-space utility nfacct(8)
The only option available for this match is the following:
--nfacct-name name
This allows you to specify the existing object name that
will be use for accounting the traffic that this rule-set
is matching.
To use this extension, you have to create an accounting object:
nfacct add http-traffic
Then, you have to attach it to the accounting object via
iptables:
iptables -I INPUT -p tcp --sport 80 -m nfacct
--nfacct-name http-traffic
iptables -I OUTPUT -p tcp --dport 80 -m nfacct
--nfacct-name http-traffic
Then, you can check for the amount of traffic that the rules
match:
nfacct get http-traffic
{ pkts = 00000000000000000156, bytes =
00000000000000151786 } = http-traffic;
You can obtain nfacct(8) from http://www.netfilter.org or,
alternatively, from the git.netfilter.org repository.
osf
The osf module does passive operating system fingerprinting. This
module compares some data (Window Size, MSS, options and their
order, TTL, DF, and others) from packets with the SYN bit set.
[!] --genre string
Match an operating system genre by using a passive
fingerprinting.
--ttl level
Do additional TTL checks on the packet to determine the
operating system. level can be one of the following
values:
• 0 - True IP address and fingerprint TTL comparison. This
generally works for LANs.
• 1 - Check if the IP header's TTL is less than the fingerprint
one. Works for globally-routable addresses.
• 2 - Do not compare the TTL at all.
--log level
Log determined genres into dmesg even if they do not match
the desired one. level can be one of the following values:
• 0 - Log all matched or unknown signatures
• 1 - Log only the first one
• 2 - Log all known matched signatures
You may find something like this in syslog:
Windows [2000:SP3:Windows XP Pro SP1, 2000 SP3]: 11.22.33.55:4024
-> 11.22.33.44:139 hops=3 Linux [2.5-2.6:] : 1.2.3.4:42624 ->
1.2.3.5:22 hops=4
OS fingerprints are loadable using the nfnl_osf program. To load
fingerprints from a file, use:
nfnl_osf -f /usr/share/xtables/pf.os
To remove them again,
nfnl_osf -f /usr/share/xtables/pf.os -d
The fingerprint database can be downloaded from
http://www.openbsd.org/cgi-bin/cvsweb/src/etc/pf.os .
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.
--suppl-groups
Causes group(s) specified with --gid-owner to be also
checked in the supplementary groups of a process.
[!] --socket-exists
Matches if the packet is associated with a socket.
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 bridged packets entering the FORWARD and
POSTROUTING chains). If the interface name ends in a "+",
then any interface which begins with this name will match.
[!] --physdev-is-in
Matches if the packet has entered through a bridge
interface.
[!] --physdev-is-out
Matches if the packet will leave through a bridge
interface.
[!] --physdev-is-bridged
Matches if the packet is being bridged and therefore is
not being routed. This is only useful in the FORWARD and
POSTROUTING chains.
pkttype
This module matches the link-layer packet type.
[!] --pkt-type {unicast|broadcast|multicast}
policy
This module 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
realm (IPv4-specific)
This matches the routing realm. Routing realms are used in
complex routing setups involving dynamic routing protocols like
BGP.
[!] --realm value[/mask]
Matches a given realm number (and optionally mask). If not
a number, value can be a named realm from
/etc/iproute2/rt_realms (mask can not be used in that
case). Both value and mask are four byte unsigned
integers and may be specified in decimal, hex (by
prefixing with "0x") or octal (if a leading zero is
given).
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.
--mask netmask
Netmask that will be applied to this recent list.
[!] --rcheck
Check if the source address of the packet is currently in
the list.
[!] --update
Like --rcheck, except it will update the "last seen"
timestamp if it matches.
[!] --remove
Check if the source address of the packet is currently in
the list and if so that address will be removed from the
list and the rule will return true. If the address is not
found, false is returned.
--seconds seconds
This option must be used in conjunction with one of
--rcheck or --update. When used, this will narrow the
match to only happen when the address is in the list and
was seen within the last given number of seconds.
--reap This option can only be used in conjunction with
--seconds. When used, this will cause entries older than
the last given number of seconds to be purged.
--hitcount hits
This option must be used in conjunction with one of
--rcheck or --update. When used, this will narrow the
match to only happen when the address is in the list and
packets had been received greater than or equal to the
given value. This option may be used along with --seconds
to create an even narrower match requiring a certain
number of hits within a specific time frame. The maximum
value for the hitcount parameter is given by the
"ip_pkt_list_tot" parameter of the xt_recent kernel
module. Exceeding this value on the command line will
cause the rule to be rejected.
--rttl This option may only be used in conjunction with one of
--rcheck or --update. When used, this will narrow the
match to only happen when the address is in the list and
the TTL of the current packet matches that of the packet
which hit the --set rule. This may be useful if you have
problems with people faking their source address in order
to DoS you via this module by disallowing others access to
your site by sending bogus packets to you.
Examples:
iptables -A FORWARD -m recent --name badguy --rcheck
--seconds 60 -j DROP
iptables -A FORWARD -p tcp -i eth0 --dport 139 -m recent
--name badguy --set -j DROP
/proc/net/xt_recent/* are the current lists of addresses and
information about each entry of each list.
Each file in /proc/net/xt_recent/ can be read from to see the
current list or written two using the following commands to
modify the list:
echo +addr >/proc/net/xt_recent/DEFAULT
to add addr to the DEFAULT list
echo -addr >/proc/net/xt_recent/DEFAULT
to remove addr from the DEFAULT list
echo / >/proc/net/xt_recent/DEFAULT
to flush the DEFAULT list (remove all entries).
The module itself accepts parameters, defaults shown:
ip_list_tot=100
Number of addresses remembered per table.
ip_pkt_list_tot=20
Number of packets per address remembered.
ip_list_hash_size=0
Hash table size. 0 means to calculate it based on
ip_list_tot, default: 512.
ip_list_perms=0644
Permissions for /proc/net/xt_recent/* files.
ip_list_uid=0
Numerical UID for ownership of /proc/net/xt_recent/*
files.
ip_list_gid=0
Numerical GID for ownership of /proc/net/xt_recent/*
files.
rpfilter
Performs a reverse path filter test on a packet. If a reply to
the packet would be sent via the same interface that the packet
arrived on, the packet will match. Note that, unlike the in-
kernel rp_filter, packets protected by IPSec are not treated
specially. Combine this match with the policy match if you want
this. Also, packets arriving via the loopback interface are
always permitted. This match can only be used in the PREROUTING
chain of the raw or mangle table.
--loose
Used to specify that the reverse path filter test should
match even if the selected output device is not the
expected one.
--validmark
Also use the packets' nfmark value when performing the
reverse path route lookup.
--accept-local
This will permit packets arriving from the network with a
source address that is also assigned to the local machine.
--invert
This will invert the sense of the match. Instead of
matching packets that passed the reverse path filter test,
match those that have failed it.
Example to log and drop packets failing the reverse path filter
test:
iptables -t raw -N RPFILTER
iptables -t raw -A RPFILTER -m rpfilter -j RETURN
iptables -t raw -A RPFILTER -m limit --limit 10/minute -j NFLOG
--nflog-prefix "rpfilter drop"
iptables -t raw -A RPFILTER -j DROP
iptables -t raw -A PREROUTING -j RPFILTER
Example to drop failed packets, without logging:
iptables -t raw -A RPFILTER -m rpfilter --invert -j DROP
rt (IPv6-specific)
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
This module matches Stream Control Transmission Protocol headers.
[!] --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.
Match types:
all Match if all given chunk types are present and flags
match.
any Match if any of the given chunk types is present with
given flags.
only Match if only the given chunk types are present with given
flags and none are missing.
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.
--return-nomatch
If the --return-nomatch option is specified and the set
type supports the nomatch flag, then the matching is
reversed: a match with an element flagged with nomatch
returns true, while a match with a plain element returns
false.
! --update-counters
If the --update-counters flag is negated, then the packet
and byte counters of the matching element in the set won't
be updated. Default the packet and byte counters are
updated.
! --update-subcounters
If the --update-subcounters flag is negated, then the
packet and byte counters of the matching element in the
member set of a list type of set won't be updated. Default
the packet and byte counters are updated.
[!] --packets-eq value
If the packet is matched an element in the set, match only
if the packet counter of the element matches the given
value too.
--packets-lt value
If the packet is matched an element in the set, match only
if the packet counter of the element is less than the
given value as well.
--packets-gt value
If the packet is matched an element in the set, match only
if the packet counter of the element is greater than the
given value as well.
[!] --bytes-eq value
If the packet is matched an element in the set, match only
if the byte counter of the element matches the given value
too.
--bytes-lt value
If the packet is matched an element in the set, match only
if the byte counter of the element is less than the given
value as well.
--bytes-gt value
If the packet is matched an element in the set, match only
if the byte counter of the element is greater than the
given value as well.
The packet and byte counters related options and flags are
ignored when the set was defined without counter support.
The option --match-set can be replaced by --set if that does not
clash with an option of other extensions.
Use of -m set requires that ipset kernel support is provided,
which, for standard kernels, is the case since Linux 2.6.39.
socket
This matches if an open TCP/UDP socket can be found by doing a
socket lookup on the packet. It matches if there is an
established or non-zero bound listening socket (possibly with a
non-local address). The lookup is performed using the packet
tuple of TCP/UDP packets, or the original TCP/UDP header embedded
in an ICMP/ICPMv6 error packet.
--transparent
Ignore non-transparent sockets.
--nowildcard
Do not ignore sockets bound to 'any' address. The socket
match won't accept zero-bound listeners by default, since
then local services could intercept traffic that would
otherwise be forwarded. This option therefore has
security implications when used to match traffic being
forwarded to redirect such packets to local machine with
policy routing. When using the socket match to implement
fully transparent proxies bound to non-local addresses it
is recommended to use the --transparent option instead.
Example (assuming packets with mark 1 are delivered locally):
-t mangle -A PREROUTING -m socket --transparent -j MARK
--set-mark 1
--restore-skmark
Set the packet mark to the matching socket's mark. Can be
combined with the --transparent and --nowildcard options
to restrict the sockets to be matched when restoring the
packet mark.
Example: An application opens 2 transparent (IP_TRANSPARENT)
sockets and sets a mark on them with SO_MARK socket option. We
can filter matching packets:
-t mangle -I PREROUTING -m socket --transparent --restore-
skmark -j action
-t mangle -A action -m mark --mark 10 -j action2
-t mangle -A action -m mark --mark 11 -j action3
state
The "state" extension is a subset of the "conntrack" module.
"state" allows access to the connection tracking state for this
packet.
[!] --state state
Where state is a comma separated list of the connection
states to match. Only a subset of the states unterstood by
"conntrack" are recognized: INVALID, ESTABLISHED, NEW,
RELATED or UNTRACKED. For their description, see the
"conntrack" heading in this manpage.
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 module matches a given string by using some pattern matching
strategy. It requires a linux kernel >= 2.6.14.
--algo {bm|kmp}
Select the pattern matching strategy. (bm = Boyer-Moore,
kmp = Knuth-Pratt-Morris)
--from offset
Set the offset from which it starts looking for any
matching. If not passed, default is 0.
--to offset
Set the offset up to which should be scanned. That is,
byte offset-1 (counting from 0) is the last one that is
scanned. If not passed, default is the packet size.
[!] --string pattern
Matches the given pattern.
[!] --hex-string pattern
Matches the given pattern in hex notation.
--icase
Ignore case when searching.
Examples:
# The string pattern can be used for simple text
characters.
iptables -A INPUT -p tcp --dport 80 -m string --algo bm
--string 'GET /index.html' -j LOG
# The hex string pattern can be used for non-printable
characters, like |0D 0A| or |0D0A|.
iptables -p udp --dport 53 -m string --algo bm --from 40
--to 57 --hex-string '|03|www|09|netfilter|03|org|00|'
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. 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. If a range is given,
the second value must be greater than or equal to the
first value.
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.).
--contiguous
When --timestop is smaller than --timestart value, match
this as a single time period instead distinct intervals.
See EXAMPLES.
--kerneltz
Use the kernel timezone instead of UTC to determine
whether a packet meets the time regulations.
About kernel timezones: Linux keeps the system time in UTC, and
always does so. On boot, system time is initialized from a
referential time source. Where this time source has no timezone
information, such as the x86 CMOS RTC, UTC will be assumed. If
the time source is however not in UTC, userspace should provide
the correct system time and timezone to the kernel once it has
the information.
Local time is a feature on top of the (timezone independent)
system time. Each process has its own idea of local time,
specified via the TZ environment variable. The kernel also has
its own timezone offset variable. The TZ userspace environment
variable specifies how the UTC-based system time is displayed,
e.g. when you run date(1), or what you see on your desktop clock.
The TZ string may resolve to different offsets at different
dates, which is what enables the automatic time-jumping in
userspace. when DST changes. The kernel's timezone offset
variable is used when it has to convert between non-UTC sources,
such as FAT filesystems, to UTC (since the latter is what the
rest of the system uses).
The caveat with the kernel timezone is that Linux distributions
may ignore to set the kernel timezone, and instead only set the
system time. Even if a particular distribution does set the
timezone at boot, it is usually does not keep the kernel timezone
offset - which is what changes on DST - up to date. ntpd will
not touch the kernel timezone, so running it will not resolve the
issue. As such, one may encounter a timezone that is always
+0000, or one that is wrong half of the time of the year. As
such, using --kerneltz is highly discouraged.
EXAMPLES. To match on weekends, use:
-m time --weekdays Sa,Su
Or, to match (once) on a national holiday block:
-m time --datestart 2007-12-24 --datestop 2007-12-27
Since the stop time is actually inclusive, you would need the
following stop time to not match the first second of the new day:
-m time --datestart 2007-01-01T17:00 --datestop
2007-01-01T23:59:59
During lunch hour:
-m time --timestart 12:30 --timestop 13:30
The fourth Friday in the month:
-m time --weekdays Fr --monthdays 22,23,24,25,26,27,28
(Note that this exploits a certain mathematical property. It is
not possible to say "fourth Thursday OR fourth Friday" in one
rule. It is possible with multiple rules, though.)
Matching across days might not do what is expected. For
instance,
-m time --weekdays Mo --timestart 23:00 --timestop 01:00
Will match Monday, for one hour from midnight to 1 a.m.,
and then again for another hour from 23:00 onwards. If
this is unwanted, e.g. if you would like 'match for two
hours from Montay 23:00 onwards' you need to also specify
the --contiguous option in the example above.
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.
ttl (IPv4-specific)
This module matches the time to live field in the IP header.
[!] --ttl-eq ttl
Matches the given TTL value.
--ttl-gt ttl
Matches if TTL is greater than the given TTL value.
--ttl-lt ttl
Matches if TTL is less than the given TTL value.
u32
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.
