Provided by: shorewall6_4.5.21.6-1_all 
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 the word 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 with only the word COMMENT.
Note
Beginning with Shorewall 4.5.11, ?COMMENT is a synonym for COMMENT and is
preferred.
SOURCE - {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}[,...]}
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.
PORT(S) (Optional) - [[!]port-name-or-number[,port-name-or-number]...]
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.
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/GROUP (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.
ORIGINAL DEST (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.
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 -
FILES
/etc/shorewall6/masq
NOTES
1. shorewall6-rtrules
http://www.shorewall.netshorewall6-rtrules.html
2. shorewall-tcrules
http://www.shorewall.netshorewall6-tcrules.html
3. shorewall6-interfaces
http://www.shorewall.netshorewall6-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.netshorewall6-exclusion.html
[FIXME: source] 01/30/2014 SHOREWALL6-MASQ(5)