Firewall Setup

Steve Greenshaw steve at softgreen.co.uk
Sat Dec 20 22:16:14 GMT 2003


Hi,

I wonder if anyone could suggest whether what I am attempting is possible?


                         INTERNET
                                 |
                          ROUTER
                        xxx.xxx.xxx.1
                                 |
               xxx.xxx.xxx.2(alias)em0
               ______FREEBSD_______
              |                                           |
           em1                           192.168.1.1 (em2)
              |                                           |
          DMZ                                PRIVATE
 xxx.xxx.xxx.xxx/24                 192.168.1.0/24


This setup is on FreeBSD 4.9 with IPFILTER and IPNAT. This choice, rather
than IPFW and NATD is so that the GUI 'fwbuilder' (www.fwbuilder.org) can be
used by several admins who are purely Windows users. At a pinch I could use
IPFW with fwbuilder and just write any NAT rules myself for NATD, but it's
much neater to have fwbuilder do the lot.

The xxx.xxx.xxx.xxx addresses are public IP's from the same single class C
network. For historical and management/manpower reasons it is just not
possible to subnet this network at present so I've set up a bridge between
em0 and em1 with em0 having an aliased address that ipnat uses for outbound
connections from the 192.168.1.0/24 network.

Preliminary testing has shown that filtering can and does take place to
allow only restricted services access to certain adresses within the DMZ,
whilst allowing the DMZ access to necessary services on the internet. NAT
works fine to allow the PRIVATE net access to the internet.

My problem is that no matter what I do (i.e. the only rule now in place is
to allow all to any via any) I cannot reach the DMZ from within the PRIVATE
network. I need to do this to get at DNS, SMTP etc. I just can't see why
this is not possible or where I am going wrong. From the firewall box itself
I get a 'no route to host' if I try to contact a machine on the DMZ. I can
contact the router though. It's as if the default route for the
xxx.xxx.xxx.xxx/24 network is via em0 (which I can understand), but I
understood that a bridge between em0 and em1 would mean that anything
broadcast on em0 would also be broadcast on em1 so allowing me access to the
DMZ.

Is there a routing entry that I'm missing somewhere? I'm not actually
setting any routes but the default gateway in rc.conf of xxx.xxx.xxx.1.

Any suggestions or pointers would be appreciated.

Cheers,

Steve.






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