Provided by: shorewall6_5.0.4-1_all bug

NAME

       masq - Shorewall6 Masquerade/SNAT definition file

SYNOPSIS

       /etc/shorewall6/masq

DESCRIPTION

       Use this file to define Source NAT (SNAT). Requires Shorewall 4.5.14 or later.

           Warning
           The entries in this file are order-sensitive. The first entry that matches a
           particular connection will be the one that is used.

           Warning
           If you have more than one ISP link, adding entries to this file will not force
           connections to go out through a particular link. You must use entries in
           shorewall6-rtrules[1](5) or PREROUTING entries in shorewall-tcrules[2](5) to do that.

       The columns in the file are as follows.

       INTERFACE:DEST - {[+]interfacelist|[:[dest-address[,dest-address]...[exclusion]]|?COMMENT}
           Outgoing interfacelist. This may be a comma-separated list of interface names. This is
           usually your internet interface.

           Each interface must match an entry in shorewall6-interfaces[3](5). Shorewall allows
           loose matches to wildcard entries in shorewall6-interfaces[3](5). For example, ppp0 in
           this file will match a shorewall6-interfaces[3](5) entry that defines ppp+.

           Where more that one internet provider share a single interface[4], the provider is
           specified by including the provider name or number in parentheses:

                       eth0(Avvanta)

           In that case, you will want to specify the interface's address for that provider in
           the ADDRESS column.

           The interface may be qualified by adding the character ":" followed by a
           comma-separated list of destination host or subnet addresses to indicate that you only
           want to change the source IP address for packets being sent to those particular
           destinations. Exclusion is allowed (see shorewall6-exclusion[5](5)) as are ipset names
           preceded by a plus sign '+'.

           Comments may be attached to Netfilter rules generated from entries in this file
           through the use of ?COMMENT lines. These lines begin with ?COMMENT; the remainder of
           the line is treated as a comment which is attached to subsequent rules until another
           ?COMMENT line is found or until the end of the file is reached. To stop adding
           comments to rules, use a line containing only ?COMMENT.

           Beginning with Shorewall 4.6.0, a new syntax is also accepted. With the exception of
           the leading '+', the interfacelist and qualifiers may appear within the parentheses of
           INLINE(...).

           Example:

                       +INLINE(eth0)

           When this is done, you may augment the rule generated by Shorewall with iptables
           matches of your own. These matches appear after a semicolon (';') at the end of the
           line.

           See example 2 below.

       SOURCE (Optional) - [interface|address[,address][exclusion]]
           Set of hosts that you wish to SNAT; one or more host or network addresses separated by
           comma. You may use ipset names preceded by a plus sign (+) to specify a set of hosts.

       ADDRESS (Optional) -
       [-|NONAT|[address-or-address-range[,address-or-address-range]...][:lowport-highport][:random][:persistent]|detect|random]
           If you do not specify an address or address range, masquerading will be performed.
           This requires Masquerade Target support in your kernel and ip6tables.

           If you specify an address here, SNAT will be used and this will be the source address.

           You may also specify a range of up to 256 IP addresses if you want the SNAT address to
           be assigned from that range in a round-robin fashion by connection. The range is
           specified by first.ip.in.range-last.ip.in.range. You may follow the port range
           with:random in which case assignment of ports from the list will be random.  random
           may also be specified by itself in this column in which case random local port
           assignments are made for the outgoing connections.

           Example: [2001:470:a:227::2]-[2001:470:a:227::10]:1000-1010

           You may follow the port range (or :random) with :persistent. This is only useful when
           an address range is specified and causes a client to be given the same
           source/destination IP pair.

           This column may not contain DNS Names.

           Normally, Netfilter will attempt to retain the source port number. You may cause
           netfilter to remap the source port by following an address or range (if any) by ":"
           and a port range with the format lowport-highport. If this is done, you must specify
           "tcp" or "udp" in the PROTO column.

           Examples:

                       [2001:470:a:787::2]:5000-6000

           If you simply place NONAT in this column, no rewriting of the source IP address or
           port number will be performed. This is useful if you want particular traffic to be
           exempt from the entries that follow in the file.

       PROTO (Optional) - {-|[!]{protocol-name|protocol-number}[,...]|+ipset}
           If you wish to restrict this entry to a particular protocol then enter the protocol
           name (from protocols(5)) or number here.

           Beginning with Shorewall 4.5.12, this column can accept a comma-separated list of
           protocols.

           Beginning with Shorewall 4.6.0, an ipset name can be specified in this column. This is
           intended to be used with bitmap:port ipsets.

       DPORT (Optional) - {-|[!]port-name-or-number[,port-name-or-number]...|+ipset}
           If the PROTO column specifies TCP (6), UDP (17), DCCP (33), SCTP (132) or UDPLITE
           (136) then you may list one or more port numbers (or names from services(5)) or port
           ranges separated by commas.

           Port ranges are of the form lowport:highport.

           Beginning with Shorewall 4.6.0, an ipset name can be specified in this column. This is
           intended to be used with bitmap:port ipsets.

       IPSEC (Optional) - [option[,option]...]
           If you specify a value other than "-" in this column, you must be running kernel 2.6
           and your kernel and iptables must include policy match support.

           Comma-separated list of options from the following. Only packets that will be
           encrypted via an SA that matches these options will have their source address changed.

           reqid=number
               where number is specified using setkey(8) using the 'unique:number option for the
               SPD level.

           spi=<number>
               where number is the SPI of the SA used to encrypt/decrypt packets.

           proto=ah|esp|ipcomp
               IPSEC Encapsulation Protocol

           mss=number
               sets the MSS field in TCP packets

           mode=transport|tunnel
               IPSEC mode

           tunnel-src=address[/mask]
               only available with mode=tunnel

           tunnel-dst=address[/mask]
               only available with mode=tunnel

           strict
               Means that packets must match all rules.

           next
               Separates rules; can only be used with strict

           yes
               When used by itself, causes all traffic that will be encrypted/encapsulated to
               match the rule.

       MARK - [!]value[/mask][:C]
           Defines a test on the existing packet or connection mark. The rule will match only if
           the test returns true.

           If you don't want to define a test but need to specify anything in the following
           columns, place a "-" in this field.

           !
               Inverts the test (not equal)

           value
               Value of the packet or connection mark.

           mask
               A mask to be applied to the mark before testing.

           :C
               Designates a connection mark. If omitted, the packet mark's value is tested.

       USER (Optional) - [!][user-name-or-number][:group-name-or-number][+program-name]
           Only locally-generated connections will match if this column is non-empty.

           When this column is non-empty, the rule matches only if the program generating the
           output is running under the effective user and/or group specified (or is NOT running
           under that id if "!" is given).

           Examples:

           joe
               program must be run by joe

           :kids
               program must be run by a member of the 'kids' group

           !:kids
               program must not be run by a member of the 'kids' group

           +upnpd
               #program named upnpd

                   Important
                   The ability to specify a program name was removed from Netfilter in kernel
                   version 2.6.14.

       SWITCH - [!]switch-name[={0|1}]
           Added in Shorewall 4.5.1 and allows enabling and disabling the rule without requiring
           shorewall restart.

           The rule is enabled if the value stored in /proc/net/nf_condition/switch-name is 1.
           The rule is disabled if that file contains 0 (the default). If '!' is supplied, the
           test is inverted such that the rule is enabled if the file contains 0.

           Within the switch-name, '@0' and '@{0}' are replaced by the name of the chain to which
           the rule is a added. The switch-name (after '@...' expansion) must begin with a letter
           and be composed of letters, decimal digits, underscores or hyphens. Switch names must
           be 30 characters or less in length.

           Switches are normally off. To turn a switch on:
               echo 1 >
                           /proc/net/nf_condition/switch-name
           To turn it off again:
               echo 0 >
                           /proc/net/nf_condition/switch-name
           Switch settings are retained over shorewall restart.

           Beginning with Shorewall 4.5.10, when the switch-name is followed by =0 or =1, then
           the switch is initialized to off or on respectively by the start command. Other
           commands do not affect the switch setting.

       ORIGDEST - [-|address[,address]...[exclusion]|exclusion]
           (Optional) This column may be included and may contain one or more addresses (host or
           network) separated by commas. Address ranges are not allowed. When this column is
           supplied, rules are generated that require that the original destination address
           matches one of the listed addresses. It is useful for specifying that SNAT should
           occur only for connections that were acted on by a DNAT when they entered the
           firewall.

           This column was formerly labelled ORIGINAL DEST.

       PROBABILITY - [probability]
           Added in Shorewall 5.0.0. When non-empty, requires the Statistics Match capability in
           your kernel and ip6tables and causes the rule to match randomly but with the given
           probability. The probability is a number 0 < probability <= 1 and may be expressed at
           up to 8 decimal points of precision.

EXAMPLES

       Example 1:
           You have a simple 'masquerading' setup where eth0 connects to a DSL or cable modem and
           eth1 connects to your local network with subnet 2001:470:b:787::0/64

           Your entry in the file will be:

                       #INTERFACE   SOURCE                  ADDRESS
                       eth0         2001:470:b:787::0/64    -

       Example 2:
           Your sit1 interface has two public IP addresses: 2001:470:a:227::1 and
           2001:470:b:227::1. You want to use the iptables statistics match to masquerade
           outgoing connections evenly between these two addresses.

               /etc/shorewall/masq:

                      #INTERFACE    SOURCE         ADDRESS
                      INLINE(sit1)  0.0.0.0/0      2001:470:a:227::1 ;  -m statistic --mode random --probability 0.50
                      sit1          0.0.0.0/0      2001:470:a:227::2

           If INLINE_MATCHES=Yes in shorewall6.conf[6](5), then these rules may be specified as
           follows:

               /etc/shorewall/masq:

                      #INTERFACE    SOURCE         ADDRESS
                      sit1          0.0.0.0/0      2001:470:a:227::1 ;  -m statistic --mode random --probability 0.50
                      sit1          0.0.0.0/0      2001:470:a:227::2

FILES

       /etc/shorewall6/masq

NOTES

        1. shorewall6-rtrules
           http://www.shorewall.net/manpages6/shorewall6-rtrules.html

        2. shorewall-tcrules
           http://www.shorewall.net/manpages6/shorewall6-tcrules.html

        3. shorewall6-interfaces
           http://www.shorewall.net/manpages6/shorewall6-interfaces.html

        4. more that one internet provider share a single interface
           http://www.shorewall.net/4.4/MultiISP.html#Shared

        5. shorewall6-exclusion
           http://www.shorewall.net/manpages6/shorewall6-exclusion.html

        6. shorewall6.conf
           http://www.shorewall.net/manpages6/shorewall6.conf.html