shorewall6-masq5masqShorewall6 Masquerade/SNAT definition file/etc/shorewall6/masqDescriptionUse this file to define Source NAT (SNAT). Requires Shorewall 4.5.14
or later.The entries in this file are order-sensitive. The first entry that
matches a particular connection will be the one that is used.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(5) or
PREROUTING entries in shorewall-tcrules(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(5).
Shorewall allows loose matches to wildcard entries in shorewall6-interfaces(5).
For example, ppp0 in this
file will match a shorewall6-interfaces(5)
entry that defines ppp+.Where more that
one internet provider share a single interface, 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)) 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.Beginning with Shorewall 4.5.11, ?COMMENT is a synonym for
COMMENT and is preferred.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 -
{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]:1000-1010You 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]:5000-6000If 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.PORT(S) (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=numberwhere 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|ipcompIPSEC Encapsulation Protocolmss=numbersets the MSS field in TCP packetsmode=transport|tunnelIPSEC modetunnel-src=address[/mask]only available with mode=tunneltunnel-dst=address[/mask]only available with mode=tunnelstrictMeans that packets must match all rules.nextSeparates rules; can only be used with strictyesWhen 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)valueValue of the packet or connection mark.maskA mask to be applied to the mark before testing.:CDesignates 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:joeprogram must be run by joe:kidsprogram must be run by a member of the 'kids'
group!:kidsprogram must not be run by a member of the 'kids'
group+upnpd#program named upnpdThe 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-nameTo turn it off again:echo 0 >
/proc/net/nf_condition/switch-nameSwitch settings are retained over shorewall
restart.Beginning with Shorewall 4.5.10, when the
switch-name is followed by
or , 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.ExamplesExample 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::0/64Your entry in the file will be: #INTERFACE SOURCE ADDRESS
eth0 2001:470:b:787::0/64 -Example 8: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(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