shorewall-masq5masqShorewall Masquerade/SNAT definition file/etc/shorewall/masqDescriptionUse this file to define dynamic NAT (Masquerading) and to define
Source NAT (SNAT).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, adding entries to this file will
*not* force connections to go out through a particular ISP. You must use
PREROUTING entries in shorewall-tcrules(5) to do
that.The columns in the file are as follows.INTERFACE - [+]interfacelist[:[digit]][:[address[,address]...[exclusion]]Outgoing interfacelist. Prior to
Shorewall 4.1.4, this must be a single interface name; in 4.1.4 and
later, this may be a comma-separated list of interface names. This
is usually your internet interface. If ADD_SNAT_ALIASES=Yes in
shorewall.conf(5), you may
add ":" and a digit to indicate that you want
the alias added with that name (e.g., eth0:0). This will allow the
alias to be displayed with ifconfig. That is
the only use for the alias name; it may not appear in any other
place in your Shorewall configuration.Each interface must match an entry in shorewall-interfaces(5).
Prior to Shorewall 4.1.4, this must be an exact match.
Shorewall-perl 4.1.4 and later allow loose matches to wildcard
entries in shorewall-interfaces(5). For
example, ppp0 in this file
will match a shorewall-interfaces(5)
entry that defines ppp+.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 shorewall-exclusion(5)).If you wish to inhibit the action of ADD_SNAT_ALIASES for this
entry then include the ":" but omit the digit: eth0:
eth2::192.0.2.32/27Normally Masq/SNAT rules are evaluated after those for
one-to-one NAT (defined in shorewall-nat(5)). If you want the
rule to be applied before one-to-one NAT rules, prefix the interface
name with "+": +eth0
+eth0:192.0.2.32/27
+eth0:2This feature should only be required if you need to insert
rules in this file that preempt entries in shorewall-nat(5).SOURCE (Formerly called SUBNET)
-
{interface[[:]exclusion]|address[,address][exclusion]}Set of hosts that you wish to masquerade. You can specify this
as an address (net or host) or as an
interface. If you give the name of an
interface, the interface must be up before you start the firewall
(Shorewall will use your main routing table to determine the
appropriate addresses to masquerade).In order to exclude a address of the specified SOURCE, you may
append an exclusion ("!" and a comma-separated
list of IP addresses (host or net) that you wish to exclude (see
shorewall-exclusion(5))).
Note that with Shorewall-perl, a colon (":") must appear between an
interface name and the
exclusion;Example (shorewall-shell):
eth1!192.168.1.4,192.168.32.0/27Example (shorewall-perl):
eth1:!192.168.1.4,192.168.32.0/27In that example traffic from eth1 would be masqueraded unless
it came from 192.168.1.4 or 196.168.32.0/27ADDRESS (Optional) - [-|NONAT|[SAME:[nodst:]][address-or-address-range[,address-or-address-range]...][:lowport-highport][:random]|detect|random]If you specify an address here, SNAT will be used and this
will be the source address. If ADD_SNAT_ALIASES is set to Yes or yes
in shorewall.conf(5) then
Shorewall will automatically add this address to the INTERFACE named
in the first column.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.
Beginning with Shorewall 4.0.6, 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: 206.124.146.177-206.124.146.180You may also use the special value "detect" which causes
Shorewall to determine the IP addresses configured on the interface
named in the INTERFACES column and substitute them in this
column.Finally, you may also specify a comma-separated list of ranges
and/or addresses in this column.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: 192.0.2.4:5000-6000
:4000-5000You can invoke the SAME target rather than the SNAT target by
prefixing the column contents with .SAME works like SNAT with the exception that the same local IP
address is assigned to each connection from a local address to a
given remote address.If the option is included, then the
same source address is used for a given internal system regardless
of which remote system is involved.Support for the SAME target is scheduled for removal from
the Linux kernel in 2008.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.If you want to leave this column empty but you need to specify
the next column then place a hyphen ("-") here.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.PORT(S) (Optional) -
[[!]port-name-or-number[,port-name-or-number]...]If the PROTO column specifies TCP (protocol 6) or UDP
(protocol 17) then you may list one or more port numbers (or names
from services(5)) separated by commas or you may list a single port
range
(lowport:highport).Where a comma-separated list is given, your kernel and
iptables must have multiport match support and a maximum of 15 ports
may be listed.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 strictMARK - [!]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. This option is only supported by
Shorewall-perl.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 192.168.0.0/24.Your entry in the file can be either: #INTERFACE SOURCE
eth0 eth1or #INTERFACE SOURCE
eth0 192.168.0.0/24Example 2:You add a router to your local network to connect subnet
192.168.1.0/24 which you also want to masquerade. You then add a
second entry for eth0 to this file: #INTERFACE SOURCE
eth0 192.168.1.0/24Example 3:You have an IPSEC tunnel through ipsec0 and you want to
masquerade packets coming from 192.168.1.0/24 but only if these
packets are destined for hosts in 10.1.1.0/24: #INTERFACE SOURCE
ipsec0:10.1.1.0/24 196.168.1.0/24Example 4:You want all outgoing traffic from 192.168.1.0/24 through eth0
to use source address 206.124.146.176 which is NOT the primary
address of eth0. You want 206.124.146.176 to be added to eth0 with
name eth0:0. #INTERFACE SOURCE ADDRESS
eth0:0 192.168.1.0/24 206.124.146.176Example 5:You want all outgoing SMTP traffic entering the firewall on
eth1 to be sent from eth0 with source IP address 206.124.146.177.
You want all other outgoing traffic from eth1 to be sent from eth0
with source IP address 206.124.146.176. #INTERFACE SOURCE ADDRESS PROTO PORT(S)
eth0 eth1 206.124.146.177 tcp smtp
eth0 eth1 206.124.146.176The order of the above two rules is significant!FILES/etc/shorewall/masqSee ALSOshorewall(8), shorewall-accounting(5), shorewall-actions(5),
shorewall-blacklist(5), shorewall-exclusion(5), shorewall-hosts(5),
shorewall-interfaces(5), shorewall-ipsec(5), shorewall-maclist(5),
shorewall-nat(5), shorewall-netmap(5), shorewall-params(5),
shorewall-policy(5), shorewall-providers(5), shorewall-proxyarp(5),
shorewall-route_rules(5), shorewall-routestopped(5), shorewall-rules(5),
shorewall.conf(5), shorewall-tcclasses(5), shorewall-tcdevices(5),
shorewall-tcrules(5), shorewall-tos(5), shorewall-tunnels(5),
shorewall-zones(5)