Firewall Setup

Kevin O'Connor kevin at
Sun Dec 21 02:53:00 GMT 2003

Steve, are you saying you have set a bridge between em0 and em1 with
both NICs having IP addresses. If this is the case it is incorrect and
will not bridge properly, only 1 of the cards in a bridge should have an
IP address assigned, in fact it will work with no IP addresses assigned.
Also you need the bridge option enabled in the kernel.

Please see the handbook

As a quick fix try setting static routes in /etc/rc.conf

-----Original Message-----
From: freebsd-users-admin at
[mailto:freebsd-users-admin at] On Behalf Of Steve Greenshaw
Sent: 20 December 2003 22:16
To: freebsd-users at
Subject: Firewall Setup


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

              |                                           |
           em1                  (em2)
              |                                           |
          DMZ                                PRIVATE       

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

The addresses are public IP's from the same single class
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
em0 and em1 with em0 having an aliased address that ipnat uses for
connections from the network.

Preliminary testing has shown that filtering can and does take place to
allow only restricted services access to certain adresses within the
whilst allowing the DMZ access to necessary services on the internet.
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
to allow all to any via any) I cannot reach the DMZ from within the
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
I get a 'no route to host' if I try to contact a machine on the DMZ. I
contact the router though. It's as if the default route for the 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

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

Any suggestions or pointers would be appreciated.



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