shorewall6-masq(5)
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][: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 2001:470:a:227::1 ; -m statistic --mode random --probability 0.50
sit1 ::/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 2001:470:a:227::1 ; -m statistic --mode random --probability 0.50
sit1 ::/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
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