SHOREWALL6-MASQ(5) | Configuration Files | SHOREWALL6-MASQ(5) |
NAME¶
snat - Shorewall6 SNAT/Masquerade definition fileSYNOPSIS¶
/etc/shorewall6/snat
DESCRIPTION¶
This file is used to define dynamic NAT (Masquerading) and to define Source NAT (SNAT). While still supported, its use is deprecated in favor of shorewall6-snat[1](5) which was introduced in Shorewall 5.0.14.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[2](5) or PREROUTING entries in shorewall-tcrules[3](5) to do that.
The columns in the file are as follows.
ACTION
MASQUERADE[+][([lowport-highport][random])]
SNAT[+]([address-or-address-range][:lowport-highport][:random][:persistent]|detect|
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: 206.124.146.177-206.124.146.180
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 feature replaces the SAME modifier which was removed from Shorewall in version 4.4.0.
You may also use the special value detect which causes Shorewall to determine the IP addresses configured on the interface named in the DEST column and substitute them in this column.
Finally, you may also specify a comma-separated list of ranges and/or addresses in this column.
DNS Names names are not allowed.
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", "udp", "dccp" or "stcp" in the PROTO column.
Example:
[2001:470:a:787::2]:5000-6000
CONTINUE[+]
action[+][(parameter,...)]
Normally Masq/SNAT rules are evaluated after those for one-to-one NAT (defined in shorewall6-nat[7](5)). If you want the rule to be applied before one-to-one NAT rules, follow the action name with "+": This feature should only be required if you need to insert rules in this file that preempt entries in shorewall6-nat[7](5).
SOURCE (Optional) - [interface|address[,address...][exclusion]]
DEST - {interface|[:[dest-address[,dest-address]...[exclusion]]|?COMMENT}
The interface must match an entry in shorewall6-interfaces[8](5). Shorewall allows loose matches to wildcard entries in shorewall6-interfaces[8](5). For example, ppp0 in this file will match a shorewall6-interfaces[8](5) entry that defines ppp+.
Where more that one internet provider share a single interface[9], 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 as the SNAT parameter.
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[10](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.
PROTO (Optional) - {-|[!]{protocol-name|protocol-number}[,...]|+ipset}
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}
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]...]
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
spi=<number>
proto=ah|esp|ipcomp
mss=number
mode=transport|tunnel
tunnel-src=address[/mask]
tunnel-dst=address[/mask]
strict
next
yes
MARK - [!]value[/mask][:C]
If you don't want to define a test but need to specify anything in the following columns, place a "-" in this field.
!
value
mask
:C
USER (Optional) - [!][user-name-or-number][:group-name-or-number][+program-name]
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
:kids
!:kids
+upnpd
Important
The ability to specify a program name was removed from Netfilter in kernel version 2.6.14.
SWITCH - [!]switch-name[={0|1}]
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:
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]
This column was formerly labelled ORIGINAL DEST.
PROBABILITY - [probability]
EXAMPLES¶
Example 1:Your entry in the file will be:
#ACTION SOURCE DEST MASQUERADE 2001:470:b:787::0/64 eth0
Example 2:
/etc/shorewall/snat: #ACTION SOURCE DEST SNAT(2001:470:a:227::1) ::/0 sit1 { probability=0.50 } SNAT(2001:470:a:227::2) ::/0 sit
FILES¶
/etc/shorewall6/snatNOTES¶
- 1.
- shorewall6-snat
- 2.
- shorewall6-rtrules
- 3.
- shorewall-tcrules
- 4.
- shorewall6.conf
- 6.
- www.shorewall.net/Actions.html
- 7.
- shorewall6-nat
- 8.
- shorewall6-interfaces
- 9.
- more that one internet provider share a single interface
- 10.
- shorewall6-exclusion
03/16/2017 | Configuration Files |