Provided by: shorewall_4.5.21.6-1_all 
NAME
nesting - Shorewall Nested Zones
SYNOPSIS
child-zone[:parent-zone[,parent-zone]...]
DESCRIPTION
In shorewall-zones[1](5), a zone may be declared to be a sub-zone of one or more other
zones using the above syntax. The child-zone may be neither the firewall zone nor a
vserver zone. The firewall zone may not appear as a parent zone, although all vserver
zones are handled as sub-zones of the firewall zone.
Where zones are nested, the CONTINUE policy in shorewall-policy[2](5) allows hosts that
are within multiple zones to be managed under the rules of all of these zones.
EXAMPLE
/etc/shorewall/zones:
#ZONE TYPE OPTION
fw firewall
net ipv4
sam:net ipv4
loc ipv4
/etc/shorewall/interfaces:
#ZONE INTERFACE BROADCAST OPTIONS
- eth0 detect dhcp,norfc1918
loc eth1 detect
/etc/shorewall/hosts:
#ZONE HOST(S) OPTIONS
net eth0:0.0.0.0/0
sam eth0:206.191.149.197
/etc/shorewall/policy:
#SOURCE DEST POLICY LOG LEVEL
loc net ACCEPT
sam all CONTINUE
net all DROP info
all all REJECT info
The second entry above says that when Sam is the client, connection requests should first
be processed under rules where the source zone is sam and if there is no match then the
connection request should be treated under rules where the source zone is net. It is
important that this policy be listed BEFORE the next policy (net to all). You can have
this policy generated for you automatically by using the IMPLICIT_CONTINUE option in
shorewall.conf[3](5).
Partial /etc/shorewall/rules:
#ACTION SOURCE DEST PROTO DEST PORT(S)
...
DNAT sam loc:192.168.1.3 tcp ssh
DNAT net loc:192.168.1.5 tcp www
...
Given these two rules, Sam can connect to the firewall's internet interface with ssh and
the connection request will be forwarded to 192.168.1.3. Like all hosts in the net zone,
Sam can connect to the firewall's internet interface on TCP port 80 and the connection
request will be forwarded to 192.168.1.5. The order of the rules is not significant.
Sometimes it is necessary to suppress port forwarding for a sub-zone. For example, suppose
that all hosts can SSH to the firewall and be forwarded to 192.168.1.5 EXCEPT Sam. When
Sam connects to the firewall's external IP, he should be connected to the firewall itself.
Because of the way that Netfilter is constructed, this requires two rules as follows:
#ACTION SOURCE DEST PROTO DEST PORT(S)
...
ACCEPT+ sam $FW tcp ssh
DNAT net loc:192.168.1.3 tcp ssh
...
The first rule allows Sam SSH access to the firewall. The second rule says that any
clients from the net zone with the exception of those in the “sam” zone should have their
connection port forwarded to 192.168.1.3. If you need to exclude more than one zone,
simply use multiple ACCEPT+ rules. This technique also may be used when the ACTION is
REDIRECT.
Care must be taken when nesting occurs as a result of the use of wildcard interfaces
(interface names ends in '+').
Here's an example. /etc/shorewall/zones:
/etc/shorewall/interfaces:
#ZONE INTERFACE BROADCAST OPTIONS
net ppp0
loc eth1
loc ppp+
dmz eth2
Because the net zone is declared before the loc zone, net is an implicit sub-zone of loc
and in the absence of a net->... CONTINUE policy, traffic from the net zone will not be
passed through loc->... rules. But DNAT and REDIRECT rules are an exception!
• DNAT and REDIRECT rules generate two Netfilter rules: a 'nat' table rule that rewrites
the destination IP address and/or port number, and a 'filter' table rule that ACCEPTs
the rewritten connection.
• Policies only affect the 'filter' table.
As a consequence, the following rules will have unexpected behavior:
#ACTION SOURCE DEST PROTO DEST
# PORT(S)
ACCEPT net dmz tcp 80
REDIRECT loc 3128 tcp 80
The second rule is intended to redirect local web requests to a proxy running on the
firewall and listening on TCP port 3128. But the 'nat' part of that rule will cause all
connection requests for TCP port 80 arriving on interface ppp+ (including ppp0!) to have
their destination port rewritten to 3128. Hence, the web server running in the DMZ will be
inaccessible from the web.
The above problem can be corrected in several ways.
The preferred way is to use the ifname pppd option to change the 'net' interface to
something other than ppp0. That way, it won't match ppp+.
If you are running Shorewall version 4.1.4 or later, a second way is to simply make the
nested zones explicit:
#ZONE TYPE OPTION
fw firewall
loc ipv4
net:loc ipv4
dmz ipv4
If you take this approach, be sure to set IMPLICIT_CONTINUE=No in shorewall.conf.
When using other Shorewall versions, another way is to rewrite the DNAT rule (assume that
the local zone is entirely within 192.168.2.0/23):
#ACTION SOURCE DEST PROTO DEST
# PORT(S)
ACCEPT net dmz tcp 80
REDIRECT loc:192.168.2.0/23 3128 tcp 80
Another way is to restrict the definition of the loc zone:
/etc/shorewall/interfaces:
#ZONE INTERFACE BROADCAST OPTIONS
net ppp0
loc eth1
- ppp+
dmz eth2
/etc/shorewall/hosts:
#ZONE HOST(S) OPTIONS
loc ppp+:192.168.2.0/23
FILES
/etc/shorewall/zones
/etc/shorewall/interfaces
/etc/shorewall/hosts
/etc/shorewall/policy
/etc/shorewall/rules
SEE ALSO
shorewall(8), shorewall-accounting(5), shorewall-actions(5), shorewall-blacklist(5),
shorewall-hosts(5), shorewall_interfaces(5), shorewall-ipsets(5), shorewall-maclist(5),
shorewall-masq(5), shorewall-nat(5), shorewall-netmap(5), shorewall-params(5),
shorewall-policy(5), shorewall-providers(5), shorewall-proxyarp(5), shorewall-rtrules(5),
shorewall-routestopped(5), shorewall-rules(5), shorewall.conf(5), shorewall-secmarks(5),
shorewall-tcclasses(5), shorewall-tcdevices(5), shorewall-tcrules(5), shorewall-tos(5),
shorewall-tunnels(5), shorewall-zones(5)
NOTES
1. shorewall-zones
http://www.shorewall.netshorewall-zones.html
2. shorewall-policy
http://www.shorewall.netshorewall-policy.html
3. shorewall.conf
http://www.shorewall.netshorewall.conf.html
[FIXME: source] 01/30/2014 SHOREWALL-NESTING(5)