한국리눅스유저그룹 > 리눅스 데탑/서버/프로그래밍 지식인QA

자기 것만 챙기는 당신은 얌체족?... 답변주시는분께 "고맙다는 감사의 코멘트"를 남겨주세요. [+10점]

전짱 [PO : 1,070]

10-04-15 12:48

iptables -t nat -A PREROUTING …

눈팅만으로는 답변글을 볼 수 없습니다. 로그인하셔야 합니다.

[게시판 맨위로]

자기 것만 챙기는 당신은 얌체족?... 답변주시는분께 "고맙다는 감사의 코멘트"를 남겨주세요. [+10점]

멀티 [PO : 188,338]

07-05-15 19:57

iptables -A FORWARD -p tcp -s …

눈팅만으로는 답변글을 볼 수 없습니다. 로그인하셔야 합니다.

iptables -A FORWARD -p tcp -s [A아아피] -d [B아이피] -j ACCEPT --dport [포트] -j ACCEPT

11번 리눅스에서 위와 같은 형식으로 포트를 포워딩 하면 되지 않을까요?

iptables 메뉴얼을 한번 보세요. ^^;;

====================

[root@CentOS ~]# man iptables > iptables.txt
[root@CentOS ~]# cat iptables.txt
IPTABLES(8)                                                        IPTABLES(8)

NAME
       iptables - administration tool for IPv4 packet filtering and NAT

SYNOPSIS
       iptables [-t table] -[AD] chain rule-specification [options]
       iptables [-t table] -I chain [rulenum] rule-specification [options]
       iptables [-t table] -R chain rulenum rule-specification [options]
       iptables [-t table] -D chain rulenum [options]
       iptables [-t table] -[LFZ] [chain] [options]
       iptables [-t table] -N chain
       iptables [-t table] -X [chain]
       iptables [-t table] -P chain target [options]
       iptables [-t table] -E old-chain-name new-chain-name

DESCRIPTION
       Iptables  is  used  to  set  up, maintain, and inspect the tables of IP
       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  ta-
       ble.

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 tar-
       get, which can be the name of a user-defined chain or one of  the  spe-
       cial 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.

TABLES
       There are currently three independent tables (which tables are  present
       at  any time depends on the kernel configuration options and which mod-
       ules are present).

-t, --table table
              This option specifies the packet matching table which  the  com-
              mand  should operate on.  If the kernel is configured with auto-
              matic module loading, an attempt will be made to load the appro-
              priate module for that table if it is not already there.

The tables are as follows:

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

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

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

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

OPTIONS
       The options that are recognized by iptables 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 iptables 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 combina-
              tion.

-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 des-
              tination names resolve to multiple addresses, the  command  will
              fail.  Rules are numbered starting at 1.

-L, --list [chain]
              List  all rules in the selected chain.  If no chain is selected,
              all chains are listed.  As  every  other  iptables  command,  it
              applies  to  the specified table (filter is the default), so NAT
              rules get listed by
               iptables -t nat -n -L
              Please note that it is often used with the -n option,  in  order
              to  avoid  long reverse DNS lookups.  It is legal to specify the
              -Z (zero) option as well, in which case  the  chain(s)  will  be
              atomically  listed  and zeroed.  The exact output is affected by
              the other arguments given. The exact rules are suppressed  until
              you use
               iptables -L -v

-F, --flush [chain]
              Flush the selected chain (all the chains in the table if none is
              given).  This is equivalent to deleting all  the  rules  one  by
              one.

-Z, --zero [chain]
              Zero the packet and byte counters in all chains.  It is legal to
              specify the -L, --list (list) option as well, to see  the  coun-
              ters 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 sec-
              tion TARGETS for the legal targets.   Only  built-in  (non-user-
              defined)  chains  can  have  policies,  and neither built-in nor
              user-defined chains can be policy targets.

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

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

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

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

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

-d, --destination [!] address[/mask]
              Destination  specification.   See  the  description  of  the  -s
              (source)  flag  for  a  detailed description of the syntax.  The
              flag --dst is an alias for this option.

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

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

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

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

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

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

OTHER OPTIONS
       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  multipli-
              ers  respectively  (but  see  the  -x flag to change this).  For
              appending, insertion,  deletion  and  replacement,  this  causes
              detailed information on the rule or rules to be printed.

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

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

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

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

MATCH EXTENSIONS
       iptables 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 mod-
       ules in one line, and you can use the -h or --help  options  after  the
       module has been specified to receive help specific to that module.

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

account
       Account traffic for all hosts in defined network/netmask.

Features:

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

- one iptables rule for all hosts in network/netmask

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

--aaddr network/netmask
              defines network/netmask for which make statistics.

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

--ashort
              table will colect only short  statistics  (only  total  counters
              without splitting it into protocols.

Example usage:

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

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

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

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

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

read counters:

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

set counters:

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

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

addrtype
       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  black-
              hole  address UNREACHABLE an unreachable address PROHIBIT a pro-
              hibited address THROW FIXME NAT FIXME XRESOLVE FIXME

--src-type type
              Matches if the source address is of given type

--dst-type type
              Matches if the destination address is of given type

ah
       This module matches the SPIs in Authentication header of IPsec packets.

--ahspi [!] spi[:spi]

childlevel
       This  is  an  experimental module.  It matches on whether the packet is
       part of a master connection or one of its children  (or  grandchildren,
       etc).   For  instance,  most packets are level 0.  FTP data transfer is
       level 1.

--childlevel [!] level

comment
       Allows you to add comments (up to 256 characters) to any rule.

--comment comment

Example:
              iptables -A INPUT -s 192.168.0.0/16 -m comment --comment "A pri-
              vatized IP block"

condition
       This matches if a specific /proc filename is ’0’ or ’1’.

--condition [!] filename
              Match  on  boolean value stored in /proc/net/ipt_condition/file-
              name file

connbytes
       Match by how many bytes or packets a connection  (or  one  of  the  two
       flows  constituting the connection) have tranferred so far, or by aver-
       age bytes per packet.

The counters are 64bit and are thus not expected to overflow ;)

The primary use is to detect long-lived downloads and mark them  to  be
       scheduled using a lower priority band in traffic control.

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

[!] --connbytes from:[to]
              match packets  from  a  connection  whose  packets/bytes/average
              packet size is more than FROM and less than TO bytes/packets. if
              TO is omitted only FROM check is done.  "!"  is  used  to  match
              packets not falling in the range.

--connbytes-dir [original|reply|both]
              which packets to consider

--connbytes-mode [packets|bytes|avgpkt]
              whether  to  check the amount of packets, number of bytes trans-
              ferred 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 TCP connections to a
       server per client IP address (or address block).

[!] --connlimit-above n
              match if the number of existing tcp connections is (not) above n

--connlimit-mask bits
              group hosts using mask

Examples:

# allow 2 telnet connections per client host
              iptables  -p tcp --syn --dport 23 -m connlimit --connlimit-above
              2 -j REJECT

# you can also match the other way around:
              iptables -p tcp --syn --dport 23  -m  connlimit  !  --connlimit-
              above 2 -j ACCEPT

#  limit  the nr of parallel http requests to 16 per class C sized net-
       work (24 bit netmask)
              iptables  -p tcp --syn --dport 80 -m connlimit --connlimit-above
              16 --connlimit-mask 24 -j REJECT

connmark
       This module matches the netfilter mark field associated with a  connec-
       tion (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).

connrate
       This module matches the current transfer rate in a connection.

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

conntrack
       This  module,  when combined with connection tracking, allows access to
       more connection tracking information than  the  "state"  match.   (this
       module is present only if iptables was compiled under a kernel support-
       ing this feature)

--ctstate state
              Where state is a comma separated list of the  connection  states
              to  match.   Possible states are INVALID meaning that the packet
              is associated with no known connection, ESTABLISHED meaning that
              the  packet is associated with a connection which has seen pack-
              ets 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 mean-
              ing that the packet is starting a new connection, but is associ-
              ated with an existing connection, such as an FTP data  transfer,
              or  an ICMP error.  SNAT A virtual state, matching if the origi-
              nal source address differs from the reply destination.   DNAT  A
              virtual state, matching if the original destination differs from
              the reply source.

--ctproto proto
              Protocol to match (by number or name)

--ctorigsrc [!] address[/mask]
              Match against original source address

--ctorigdst [!] address[/mask]
              Match against original destination address

--ctreplsrc [!] address[/mask]
              Match against reply source address

--ctrepldst [!] address[/mask]
              Match against reply destination address

--ctstatus [NONE|EXPECTED|SEEN_REPLY|ASSURED][,...]
              Match against internal conntrack states

--ctexpire time[:time]
              Match remaining lifetime in seconds against given value or range
              of values (inclusive)

dccp
       --source-port,--sport [!] port[:port]

--destination-port,--dport [!] port[:port]

--dccp-types [!] mask
              Match  when  the  DCCP packet type is one of ’mask’. ’mask’ is a
              comma-separated list of packet types.  Packet types are: REQUEST
              RESPONSE  DATA  ACK  DATAACK  CLOSEREQ  CLOSE RESET SYNC SYNCACK
              INVALID.

--dccp-option [!] number
              Match if DCP option set.

dscp
       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 [0-32].

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

dstlimit
       This  module  allows you to limit the packet per second (pps) rate on a
       per destination IP or per destination port base.   As  opposed  to  the
       ‘limit’  match,  every  destination  ip / destination port has it’s own
       limit.

THIS MODULE IS DEPRECATED AND HAS BEEN REPLACED BY ‘‘hashlimit’’

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

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

--dstlimit-name name
              Name for /proc/net/ipt_dstlimit/* file entry

[--dstlimit-burst burst]
              Number of packets to match in a burst.  Default: 5

[--dstlimit-htable-size size]
              Number of buckets in the hashtable

[--dstlimit-htable-max max]
              Maximum number of entries in the hashtable

[--dstlimit-htable-gcinterval interval]
              Interval  between  garbage  collection runs of the hashtable (in
              miliseconds).  Default is 1000 (1 second).

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

ecn
       This  allows you to match the ECN bits of the IPv4 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 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]

fuzzy
       This  module  matches  a  rate  limit based on a fuzzy logic controller
       [FLC]

--lower-limit number
              Specifies the lower limit (in packets per second).

--upper-limit number
              Specifies the upper limit (in packets per second).

hashlimit
       This patch adds a new match called ’hashlimit’.  The idea  is  to  have
       something  like  ’limit’,  but  either  per destination-ip or per (des-
       tip,destport) tuple.

It gives you the ability to express

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

’100 packets per second for every service of 192.168.1.1’

with a single iptables rule.

--hashlimit rate
              A rate just like the limit match

--hashlimit-burst num
              Burst value, just like limit match

--hashlimit-mode destip | destip-destport
              Limit per IP or per port

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

--hashlimit-htable-size num
              The number of buckets of the hash table

--hashlimit-htable-max num
              Maximum entries in the hash

--hashlimit-htable-expire num
              After how many miliseconds do hash entries expire

--hashlimit-htable-gcinterval num
              How many miliseconds between garbage collection intervals

helper
       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.

icmp
       This extension is loaded if ‘--protocol icmp’ is  specified.   It  pro-
       vides the following option:

--icmp-type [!] typename
              This  allows  specification  of  the  ICMP  type, which can be a
              numeric ICMP type, or one of the ICMP type names  shown  by  the
              command
               iptables -p icmp -h

iprange
       This matches on a given arbitrary range of IPv4 addresses

[!]--src-range ip-ip
              Match source IP in the specified range.

[!]--dst-range ip-ip
              Match destination IP in the specified range.

ipv4options
       Match  on IPv4 header options like source routing, record route, times-
       tamp and router-alert.

--ssrr To match packets with the flag strict source routing.

--lsrr To match packets with the flag loose source routing.

--no-srr
              To match packets with no flag for source routing.

[!] --rr
              To match packets with the RR flag.

[!] --ts
              To match packets with the TS flag.

[!] --ra
              To match packets with the router-alert option.

[!] --any-opt
              To match a packet with at least one IP option, or no  IP  option
              at all if ! is chosen.

Examples:

$ iptables -A input -m ipv4options --rr -j DROP
              will drop packets with the record-route flag.

$ iptables -A input -m ipv4options --ts -j DROP
              will drop packets with the timestamp flag.

length
       This  module matches the length 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
       (unless the ‘!’ flag is used).  It can be used in combination with  the
       LOG target to give limited logging, for example.

--limit rate
              Maximum  average  matching  rate: specified as a number, with an
              optional ‘/second’, ‘/minute’, ‘/hour’, or  ‘/day’  suffix;  the
              default is 3/hour.

--limit-burst number
              Maximum  initial  number  of  packets to match: this number gets
              recharged by one every time the limit  specified  above  is  not
              reached, up to this number; the default is 5.

mac
       --mac-source [!] address
              Match   source   MAC   address.    It   must   be  of  the  form
              XX:XX:XX:XX:XX:XX.  Note that this only makes sense for  packets
              coming from an Ethernet device and entering the PREROUTING, FOR-
              WARD 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 com-
              parison).

mport
       This  module  matches  a  set of source or destination ports.  Up to 15
       ports can be specified.  It can only be used in conjunction with -p tcp
       or -p udp.

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

--destination-ports port[,port[,port...]]
              Match if the destination port is one of the  given  ports.   The
              flag --dports is a convenient alias for this option.

--ports port[,port[,port...]]
              Match  if the both the source and destination ports are equal to
              each other and to one of the given ports.

multiport
       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 [!] port[,port[,port:port...]]
              Match if the source port is one of the given  ports.   The  flag
              --sports is a convenient alias for this option.

--destination-ports [!] port[,port[,port:port...]]
              Match  if  the  destination port is one of the given ports.  The
              flag --dports is a convenient alias for this option.

--ports [!] port[,port[,port:port...]]
              Match if either the source or destination ports are equal to one
              of the given ports.

nth
       This module matches every ‘n’th packet

--every value
              Match every ‘value’ packet

[--counter num]
              Use internal counter number ‘num’.  Default is ‘0’.

[--start num]
              Initialize the counter at the number ‘num’ insetad of ‘0’.  Most
              between ‘0’ and ‘value’-1.

[--packet num]
              Match on ‘num’ packet.  Most be between ‘0’ and ‘value’-1.

osf
       The idea of passive OS fingerprint matching exists  for  quite  a  long
       time,  but  was created as extension fo OpenBSD pf only some weeks ago.
       Original  idea  was  lurked  in  some  OpenBSD  mailing  list   (thanks
       grange@open...)  and  than  adopted for Linux netfilter in form of this
       code.

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

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

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

In syslog you find something like this:

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

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

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

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

--genre [!] string
              Match a OS genre by passive fingerprinting

Example:

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

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

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

echo -en FLUSH > /proc/sys/net/ipv4/osf

Only one fingerprint per open/write/close.

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

owner
       This  module  attempts  to  match various characteristics of the packet
       creator, for locally-generated packets.  It is only valid in the OUTPUT
       chain,  and  even  this  some packets (such as ICMP ping responses) may
       have no owner, and hence never match.

--uid-owner userid
              Matches if the packet was created by a process  with  the  given
              effective user id.

--gid-owner groupid
              Matches  if  the  packet was created by a process with the given
              effective group id.

--pid-owner processid
              Matches if the packet was created by a process  with  the  given
              process id.

--sid-owner sessionid
              Matches if the packet was created by a process in the given ses-
              sion group.

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

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

physdev
       This module matches  on  the  bridge  port  input  and  output  devices
       enslaved  to  a bridge device. This module is a part of the infrastruc-
       ture 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  inter-
              face  which  begins  with this name will match. Note that in the
              nat and mangle OUTPUT chains one cannot match on the bridge out-
              put  port,  however  one  can in the filter OUTPUT chain. If the
              packet won’t leave by a bridge device or it is yet unknown  what
              the  output  device  will  be,  then the packet won’t match this
              option, unless

[!] --physdev-is-in
              Matches if the packet has entered through a bridge interface.

[!] --physdev-is-out
              Matches if the packet will leave through a bridge interface.

[!] --physdev-is-bridged
              Matches if the packet is being  bridged  and  therefore  is  not
              being  routed.  This is only useful in the FORWARD and POSTROUT-
              ING 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  decapsula-
              tion  or  the policy that will be used for encapsulation.  in is
              valid in the PREROUTING, INPUT and FORWARD chains, out is  valid
              in the POSTROUTING, OUTPUT and FORWARD chains.

--pol none|ipsec
              Matches if the packet is subject to IPsec processing.

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

--reqid id
              Matches the reqid of the policy rule. The reqid can be specified
              with setkey(8) using unique:id as level.

--spi spi
              Matches the SPI of the SA.

--proto ah|esp|ipcomp
              Matches the encapsulation protocol.

--mode tunnel|transport
              Matches the encapsulation mode.

--tunnel-src addr[/mask]
              Matches  the source end-point address of a tunnel mode SA.  Only
              valid with --mode tunnel.

--tunnel-dst addr[/mask]
              Matches the destination end-point address of a tunnel  mode  SA.
              Only valid with --mode tunnel.

--next Start  the next element in the policy specification. Can only be
              used with --strict

psd
       Attempt to detect TCP and UDP port scans. This match was  derived  from
       Solar Designer’s scanlogd.

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

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

--psd-lo-ports-weight weight
              Weight  of the packet with privileged (<=1024) destination port.

--psd-hi-ports-weight weight
              Weight of the packet with non-priviliged destination port.

quota
       Implements network quotas by decrementing  a  byte  counter  with  each
       packet.

--quota bytes
              The quota in bytes.

KNOWN BUGS: this does not work on SMP systems.

random
       This module randomly matches a certain percentage of all packets.

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

realm
       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).

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.

--name name
              Specify the list to use for the commands. If no  name  is  given
              then ’DEFAULT’ will be used.

[!] --set
              This  will  add the source address of the packet to the list. If
              the source address is already in the list, this will update  the
              existing  entry.  This will always return success (or failure if
              ‘!’ is passed in).

[!] --rcheck
              Check if the source address of the packet is  currently  in  the
              list.

[!] --update
              Like  --rcheck,  except it will update the "last seen" timestamp
              if it matches.

[!] --remove
              Check if the source address of the packet is  currently  in  the
              list  and  if  so that address will be removed from the list and
              the rule will return true. If the address is not found, false is
              returned.

[!] --seconds seconds
              This  option must be used in conjunction with one of --rcheck or
              --update. When used, this will narrow the match to  only  happen
              when  the  address  is  in the list and was seen within the last
              given number of seconds.

[!] --hitcount hits
              This option must be used in conjunction with one of --rcheck  or
              --update.  When  used, this will narrow the match to only happen
              when the address is in the list and packets  had  been  received
              greater  than  or  equal  to the given value. This option may be
              used along with --seconds  to  create  an  even  narrower  match
              requiring a certain number of hits within a specific time frame.

--rttl This option must be used in conjunction with one of --rcheck  or
              --update.  When  used, this will narrow the match to only happen
              when the address is in the list  and  the  TTL  of  the  current
              packet matches that of the packet which hit the --set rule. This
              may be useful if you have  problems  with  people  faking  their
              source  address in order to DoS you via this module by disallow-
              ing others access to your site by sending bogus packets to  you.

Examples:

# iptables -A FORWARD -m recent --name badguy --rcheck --seconds
              60 -j DROP

# iptables -A FORWARD -p tcp  -i  eth0  --dport  139  -m  recent
              --name badguy --set -j DROP

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

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

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

echo xx.xx.xx.xx > /proc/net/ipt_recent/DEFAULT
              to Add to the DEFAULT list

echo -xx.xx.xx.xx > /proc/net/ipt_recent/DEFAULT
              to Remove from the DEFAULT list

echo clear > /proc/net/ipt_recent/DEFAULT
              to empty the DEFAULT list.

The module itself accepts parameters, defaults shown:

ip_list_tot=100
              Number of addresses remembered per table

ip_pkt_list_tot=20
              Number of packets per address remembered

ip_list_hash_size=0
              Hash table size. 0 means to calculate it based  on  ip_list_tot,
              default: 512

ip_list_perms=0644
              Permissions for /proc/net/ipt_recent/* files

debug=0
              Set to 1 to get lots of debugging info

sctp
       --source-port,--sport [!] port[:port]

--destination-port,--dport [!] port[:port]

--chunk-types [!] all|any|only chunktype[:flags] [...]
              The  flag  letter  in  upper  case indicates that the flag is to
              match if set, in the lower case indicates to match if unset.

Chunk types: DATA INIT  INIT_ACK  SACK  HEARTBEAT  HEARTBEAT_ACK
              ABORT   SHUTDOWN   SHUTDOWN_ACK   ERROR  COOKIE_ECHO  COOKIE_ACK
              ECN_ECNE ECN_CWR SHUTDOWN_COMPLETE ASCONF ASCONF_ACK

chunk type            available flags
              DATA                  U B E u b e
              ABORT                 T t
              SHUTDOWN_COMPLETE     T t

(lowercase means flag should be "off", uppercase means "on")

Examples:

iptables -A INPUT -p sctp --dport 80 -j DROP

iptables -A INPUT -p sctp --chunk-types any DATA,INIT -j DROP

iptables -A INPUT -p sctp --chunk-types any DATA:Be -j ACCEPT

set
       This modules macthes IP sets which can be defined by ipset(8).

--set setname flag[,flag...]
              where flags are src and/or dst and there can be no more than six
              of them. Hence the command
               iptables -A FORWARD -m set --set test src,dst
              will match packets, for which (depending on the type of the set)
              the source address or port number of the packet can be found  in
              the specified set. If there is a binding belonging to the mached
              set element or there is a default binding  for  the  given  set,
              then  the  rule  will  match  the  packet  only  if additionally
              (depending on the type of the set) the  destination  address  or
              port  number  of the packet can be found in the set according to
              the binding.

state
       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 associ-
              ated with a connection which has seen  packets  in  both  direc-
              tions, NEW meaning that the packet has started a new connection,
              or otherwise associated with a connection  which  has  not  seen
              packets  in both directions, and RELATED meaning that the packet
              is starting a new connection, but is associated with an existing
              connection, such as an FTP data transfer, or an ICMP error.

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

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

tcp
       These extensions are loaded if ‘--protocol tcp’ is specified.  It  pro-
       vides the following options:

--source-port [!] port[:port]
              Source  port  or  port range specification. This can either be a
              service name or a port number. An inclusive range  can  also  be
              specified,  using  the  format  port:port.  If the first port is
              omitted, "0" is assumed; if the  last  is  omitted,  "65535"  is
              assumed.  If the second port greater then the first they will be
              swapped.  The flag  --sport  is  a  convenient  alias  for  this
              option.

--destination-port [!] port[:port]
              Destination  port or port range specification.  The flag --dport
              is a convenient alias for this option.

--tcp-flags [!] mask comp
              Match when the TCP flags are as specified.  The  first  argument
              is  the  flags which we should examine, written as a comma-sepa-
              rated list, and the second argument is a comma-separated list of
              flags which must be set.  Flags are: SYN ACK FIN RST URG PSH ALL
              NONE.  Hence the command
               iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN
              will only match packets with the SYN flag set, and the ACK,  FIN
              and RST flags unset.

[!] --syn
              Only  match TCP packets with the SYN bit set and the ACK,RST and
              FIN bits cleared.  Such packets are used to request TCP  connec-
              tion initiation; for example, blocking such packets coming in an
              interface will prevent incoming TCP  connections,  but  outgoing
              TCP  connections will be unaffected.  It is equivalent to --tcp-
              flags  SYN,RST,ACK,FIN  SYN.   If  the  "!"  flag  precedes  the
              "--syn", the sense of the option is inverted.

--tcp-option [!] number
              Match if TCP option set.

--mss value[:value]
              Match  TCP  SYN  or SYN/ACK packets with the specified MSS value
              (or range), which control the maximum packet size for that  con-
              nection.

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 facultative.

--timestart value
              Match  only  if  it is after ‘value’ (Inclusive, format: HH:MM ;
              default 00:00).

--timestop  value
              Match only if it is before ‘value’ (Inclusive, format:  HH:MM  ;
              default 23:59).

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

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

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

tos
       This module matches the 8 bits of Type  of  Service  field  in  the  IP
       header (ie. including the precedence bits).

--tos tos
              The argument is either a standard name, (use
               iptables -m tos -h
              to see the list), or a numeric value to match.

ttl
       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  allows  you  to extract quantities of up to 4 bytes from a packet,
       AND them with specified masks, shift them by specified amounts and test
       whether the results are in any of a set of specified ranges.  The spec-
       ification of what to extract is general enough  to  skip  over  headers
       with lengths stored in the packet, as in IP or TCP header lengths.

Details and examples are in the kernel module source.

udp
       These  extensions are loaded if ‘--protocol udp’ is specified.  It pro-
       vides the following options:

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

--destination-port [!] port[:port]
              Destination  port or port range specification.  See the descrip-
              tion of the --destination-port option of the TCP  extension  for
              details.

unclean
       This  module takes no options, but attempts to match packets which seem
       malformed or unusual.  This is regarded as experimental.

TARGET EXTENSIONS
       iptables can use extended target modules: the following are included in
       the standard distribution.

BALANCE
       This  allows  you to DNAT connections in a round-robin way over a given
       range of destination addresses.

--to-destination ipaddr-ipaddr
              Address range to round-robin over.

CLASSIFY
       This module allows you to set the skb->priority value (and  thus  clas-
       sify the packet into a specific CBQ class).

--set-class MAJOR:MINOR
              Set the major and minor class value.

CLUSTERIP
       This  module  allows  you  to  configure a simple cluster of nodes that
       share a certain IP and MAC address without an explicit load balancer in
       front  of  them.   Connections  are  statically distributed between the
       nodes in this cluster.

--new  Create a new ClusterIP.  You always have  to  set  this  on  the
              first rule for a given ClusterIP.

--hashmode mode
              Specify  the hashing mode.  Has to be one of sourceip, sourceip-
              sourceport, sourceip-sourceport-destport

--clustermac mac
              Specify the ClusterIP MAC address.  Has to be a link-layer  mul-
              ticast address

--total-nodes num
              Number of total nodes within this cluster.

--local-node num
              Local node number within this cluster.

--hash-init rnd
              Specify the random seed used for hash initialization.

CONNMARK
       This module sets the netfilter mark value associated with a connection

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

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

--restore-mark [--mask mask]
              Copy the connection mark value to the packet. If a mask is spec-
              ified then only those bits are copied. This is only valid in the
              mangle table.

DNAT
       This  target is only valid in the nat table, in the PREROUTING and OUT-
       PUT chains, and user-defined chains which are only  called  from  those
       chains.  It specifies that the destination address of the packet should
       be modified (and all future packets in this  connection  will  also  be
       mangled),  and rules should cease being examined.  It takes one type of
       option:

--to-destination ipaddr[-ipaddr][:port-port]
              which can specify a single new destination IP address, an inclu-
              sive  range of IP addresses, and optionally, a port range (which
              is only valid if the rule also specifies -p tcp or -p udp).   If
              no port range is specified, then the destination port will never
              be modified.

In Kernels up to 2.6.10 you  can  add  several  --to-destination
              options.  For those kernels, if you specify more than one desti-
              nation address, either via an address range  or  multiple  --to-
              destination  options, a simple round-robin (one after another in
              cycle) load  balancing  takes  place  between  these  addresses.
              Later  Kernels  (>= 2.6.11-rc1) don’t have the ability to NAT to
              multiple ranges anymore.

DSCP
       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.

ECN
       This target allows to selectively work around known ECN blackholes.  It
       can only be used in the mangle table.

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

IPMARK
       Allows you to mark a received packet basing on its IP address. This can
       replace  many  mangle/mark  entries  with only one, if you use firewall
       based classifier.

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

--addr src/dst
              Use source or destination IP address.

--and-mask mask
              Perform bitwise ‘and’ on the IP address and this mask.

--or-mask mask
              Perform bitwise ‘or’ on the IP address and this mask.

The  order  of  IP  address  bytes  is reversed to meet "human order of
       bytes": 192.168.0.1 is 0xc0a80001. At first the ‘and’ operation is per-
       formed, then ‘or’.

Examples:

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

We have one classifier rule:

tc filter add dev eth3 parent 1:0 protocol ip fw

Earlier we had many rules just like below:

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

iptables -t mangle -A POSTROUTING -o eth3 -d 192.168.5.3 -j MARK
              --set-mark 0x10503

Using  IPMARK target we can replace all the mangle/mark rules with only
       one:

iptables -t mangle -A POSTROUTING -o eth3 -j  IPMARK  --addr=dst
              --and-mask=0xffff --or-mask=0x10000

On  the routers with hundreds of users there should be significant load
       decrease (e.g. twice).

IPV4OPTSSTRIP
       Strip all the IP options from a packet.

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

# iptables -t mangle -A PREROUTING -j IPV4OPTSSTRIP

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  match-
       ing  packets  (like most IP header fields) via the kernel log (where it
       can be read with dmesg or syslogd(8)).  This is a "non-terminating tar-
       get",  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 IP packet header.

--log-uid
              Log the userid of the process which generated the packet.

MARK
       This  is  used  to  set  the  netfilter  mark value associated with the
       packet.  It is only valid in the mangle table.  It can for  example  be
       used in conjunction with iproute2.

--set-mark mark

MASQUERADE
       This  target  is only valid in the nat table, in the POSTROUTING chain.
       It should only be used with dynamically assigned  IP  (dialup)  connec-
       tions: if you have a static IP address, you should use the SNAT target.
       Masquerading is equivalent to specifying a mapping to the IP address of
       the  interface  the  packet  is going out, but also has the effect that
       connections are forgotten when the interface goes down.   This  is  the
       correct  behavior  when  the  next  dialup is unlikely to have the same
       interface address (and hence any established connections are lost  any-
       way).  It takes one option:

--to-ports port[-port]
              This  specifies  a  range of source ports to use, overriding the
              default SNAT source port-selection heuristics (see above).  This
              is only valid if the rule also specifies -p tcp or -p udp.

MIRROR
       This  is  an experimental demonstration target which inverts the source
       and destination fields in the IP header and retransmits the packet.  It
       is  only  valid  in the INPUT, FORWARD and PREROUTING chains, and user-
       defined chains which are only called from those chains.  Note that  the
       outgoing  packets  are NOT seen by any packet filtering chains, connec-
       tion tracking or NAT, to avoid loops and other problems.

NETMAP
       This target allows you to statically map a whole network  of  addresses
       onto  another  network of addresses.  It can only be used from rules in
       the nat table.

--to address[/mask]
              Network address to map to.  The resulting address will  be  con-
              structed  in  the  following way: All ’one’ bits in the mask are
              filled in from the new ‘address’.  All bits that are zero in the
              mask are filled in from the original address.

NFQUEUE
       This  target  is an extension of the QUEUE target. As opposed to QUEUE,
       it allows you to put a packet into any specific  queue,  identified  by
       its 16-bit queue number.

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

It can only be used with Kernel versions  2.6.14  or  later,  since  it
       requires
              the nfnetlink_queue kernel support.

NOTRACK
       This target disables connection tracking for all packets matching  that
       rule.

It can only be used in the
              raw table.

REDIRECT
       This  target is only valid in the nat table, in the PREROUTING and OUT-
       PUT chains, and user-defined chains which are only  called  from  those
       chains.   It redirects the packet to the machine itself by changing the
       destination IP  to  the  primary  address  of  the  incoming  interface
       (locally-generated  packets  are  mapped to the 127.0.0.1 address).  It
       takes one option:

--to-ports port[-port]
              This specifies a destination port or  range  of  ports  to  use:
              without  this,  the  destination port is never altered.  This is
              only valid if the rule also specifies -p tcp or -p udp.

REJECT
       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 TAR-
       GET, 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
               icmp-net-unreachable
               icmp-host-unreachable
               icmp-port-unreachable
               icmp-proto-unreachable
               icmp-net-prohibited
               icmp-host-prohibited or
               icmp-admin-prohibited (*)
              which  return  the appropriate ICMP error message (port-unreach-
              able is the default).  The option tcp-reset can be used on rules
              which  only match the TCP protocol: this causes a TCP RST packet
              to be sent back.  This  is  mainly  useful  for  blocking  ident
              (113/tcp)  probes  which  frequently  occur when sending mail to
              broken mail hosts (which won’t accept your mail otherwise).

(*) Using icmp-admin-prohibited with kernels that  do  not  support  it
       will result in a plain DROP instead of REJECT

ROUTE
       This is used to explicitly override the core  network  stack’s  routing
       decision.  mangle table.

--oif ifname
              Route the packet through ‘ifname’ network interface

--iif ifname
              Change the packet’s incoming interface to ‘ifname’

--gw IP_address
              Route the packet via this gateway

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

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

SAME
       Similar  to SNAT/DNAT depending on chain: it takes a range of addresses
       (‘--to 1.2.3.4-1.2.3.7’) and gives a client the  same  source-/destina-
       tion-address for each connection.

--to <ipaddr>-<ipaddr>
              Addresses  to map source to. May be specified more than once for
              multiple ranges.

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

SET
       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 and there can be no more than six
              of them.

The bindings to follow must previously be defined in order to use
              multilevel adding/deleting by the SET target.

SNAT
       This target is only valid in the nat table, in the  POSTROUTING  chain.
       It  specifies  that the source address of the packet should be modified
       (and all future packets in this connection will also be  mangled),  and
       rules should cease being examined.  It takes one type of option:

--to-source  ipaddr[-ipaddr][:port-port]
              which  can  specify a single new source IP address, an inclusive
              range of IP addresses, and optionally, a port  range  (which  is
              only  valid if the rule also specifies -p tcp or -p udp).  If no
              port range is specified, then source ports  below  512  will  be
              mapped  to  other  ports  below  512: those between 512 and 1023
              inclusive will be mapped to ports below 1024,  and  other  ports
              will  be mapped to 1024 or above. Where possible, no port alter-
              ation will occur.

In Kernels  up  to  2.6.10,  you  can  add  several  --to-source
              options.  For those kernels, if you specify more than one source
              address, either via an address  range  or  multiple  --to-source
              options, a simple round-robin (one after another in cycle) takes
              place between these addresses.  Later  Kernels  (>=  2.6.11-rc1)
              don’t have the ability to NAT to multiple ranges anymore.

TARPIT
       Captures  and holds incoming TCP connections using no local per-connec-
       tion resources. Connections are accepted, but immediately  switched  to
       the persist state (0 byte window), in which the remote side stops send-
       ing data and asks to continue every 60-240 seconds.  Attempts to  close
       the  connection  are  ignored,  forcing the remote side to time out the
       connection in 12-24 minutes.

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

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

iptables -A INPUT -p tcp -m tcp --dport 80 -j TARPIT

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

iptables -A FORWARD -p tcp -j TARPIT

iptables -A FORWARD -j DROP

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

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

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

TCPMSS
       This target allows to alter the MSS value of TCP SYN packets,  to  con-
       trol  the maximum size for that connection (usually limiting it to your
       outgoing interface’s MTU minus 40).  Of course, it can only be used  in
       conjunction with -p tcp.  It is only valid in the mangle table.
       This  target  is  used to overcome criminally braindead ISPs or servers
       which block ICMP Fragmentation Needed 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  con-
       figuration like:
        iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN \
                    -j TCPMSS --clamp-mss-to-pmtu

--set-mss value
              Explicitly set MSS option to specified value.

--clamp-mss-to-pmtu
              Automatically clamp MSS value to (path_MTU - 40).

These options are mutually exclusive.

TOS
       This  is  used to set the 8-bit Type of Service field in the IP header.
       It is only valid in the mangle table.

--set-tos tos
              You can use a numeric TOS values, or use
               iptables -j TOS -h
              to see the list of valid TOS names.

TRACE
       This target has no options.  It just turns on packet  tracing  for  all
       packets that match this rule.

TTL
       This is used to modify the IPv4 TTL header field.  The TTL field deter-
       mines how many hops (routers) a packet can traverse until it’s time  to
       live is exceeded.

Setting  or  incrementing the TTL field can potentially be very danger-
       ous,
              so it should be avoided at any cost.

Don’t  ever set or increment the value on packets that leave your local
       network!
              mangle table.

--ttl-set value
              Set the TTL value to ‘value’.

--ttl-dec value
              Decrement the TTL value ‘value’ times.

--ttl-inc value
              Increment the TTL value ‘value’ times.

ULOG
       This  target provides userspace logging of matching packets.  When this
       target is set for a rule, the Linux kernel will multicast  this  packet
       through a netlink socket. One or more userspace processes may then sub-
       scribe to various multicast groups and receive the packets.  Like  LOG,
       this  is  a  "non-terminating target", i.e. rule traversal continues at
       the next rule.

--ulog-nlgroup nlgroup
              This specifies the netlink group (1-32) to which the  packet  is
              sent.  Default value is 1.

--ulog-prefix prefix
              Prefix  log messages with the specified prefix; up to 32 charac-
              ters long, and useful for distinguishing messages in the logs.

--ulog-cprange size
              Number of bytes to be copied to userspace.  A value of 0  always
              copies the entire packet, regardless of its size.  Default is 0.

--ulog-qthreshold size
              Number of packet to queue inside kernel.  Setting this value to,
              e.g.  10 accumulates ten packets inside the kernel and transmits
              them as one netlink multipart message to userspace.  Default  is
              1 (for backwards compatibility).

XOR
       Encrypt TCP and UDP traffic using a simple XOR encryption

--key string
              Set key to "string"

--block-size
              Set block size

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.

BUGS
       Bugs?  What’s this? ;-)  Well,  you  might  want  to  have  a  look  at
       http://bugzilla.netfilter.org/

COMPATIBILITY WITH IPCHAINS
       This  iptables  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.

iptables is a pure packet filter when using the default ‘filter’ table,
       with optional extension modules.  This should simplify much of the pre-
       vious confusion over the combination of IP masquerading and packet fil-
       tering  seen  previously.  So the following options are handled differ-
       ently:
        -j MASQ
        -M -S
        -M -L
       There are several other changes in iptables.

SEE ALSO
       iptables-save(8), iptables-restore(8), ip6tables(8), ip6tables-save(8),
       ip6tables-restore(8), libipq(3).

The packet-filtering-HOWTO details iptables usage for packet filtering,
       the NAT-HOWTO details NAT, the netfilter-extensions-HOWTO  details  the
       extensions  that  are not in the standard distribution, and the netfil-
       ter-hacking-HOWTO details the netfilter internals.
       See http://www.netfilter.org/.

AUTHORS
       Rusty Russell originally 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 every-
       where.

James Morris wrote the TOS target, and tos match.

Jozsef Kadlecsik wrote the REJECT target.

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

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

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

Mar 09, 2002                      IPTABLES(8)
[root@CentOS ~]#

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NodPlayer [PO : 74,429]

07-05-15 14:50

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