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       nesting - Shorewall Nested Zones




       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.

       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.



                   #ZONE    TYPE        OPTION
                   fw       firewall
                   net      ipv4
                   sam:net  ipv4
                   loc      ipv4


                   #ZONE     INTERFACE     BROADCAST     OPTIONS
                   -         eth0          detect        dhcp,norfc1918
                   loc       eth1          detect


                   #ZONE     HOST(S)                     OPTIONS
                   net       eth0:
                   sam       eth0:


                   #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: tcp      ssh
                   DNAT      net       loc: 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 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 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 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: 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 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:


                   #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

       When using other Shorewall versions, another way is to rewrite the DNAT
       rule (assume that the local zone is entirely within

                   #ACTION     SOURCE                 DEST      PROTO      DEST
                   #                                                       PORT(S)
                   ACCEPT      net                    dmz       tcp        80
                   REDIRECT    loc:     3128      tcp        80

       Another way is to restrict the definition of the loc zone:


                   #ZONE    INTERFACE      BROADCAST        OPTIONS
                   net      ppp0
                   loc      eth1
                   -        ppp+
                   dmz      eth2


                   #ZONE    HOST(S)             OPTIONS
                   loc      ppp+:








       shorewall(8), shorewall-accounting(5), shorewall-actions(5),
       shorewall-blacklist(5), shorewall-hosts(5), shorewall-interfaces(5),
       shorewall-ipsec(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-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)


        1. shorewall-zones

        2. shorewall-policy

        3. shorewall.conf

[FIXME: source]                   06/17/2010