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Date:      Sun, 15 Oct 2000 08:51:50 +0200
From:      Thierry Herbelot <herbelot@cybercable.fr>
To:        Gregory Sutter <gsutter@zer0.org>
Cc:        hackers@FreeBSD.ORG
Subject:   Re: Routing issues
Message-ID:  <39E95406.8F1C0717@cybercable.fr>
References:  <20001014233212.H3444@klapaucius.zer0.org>

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Gregory Sutter wrote:
> 
> I'm setting up a network that looks like this:
> 
> --Internet----Router---Firewall
>                           |
>                           |               /--- host
>                        Switch----NAT-----<----- host
>                           |               \----- host
>                           |                \----- etc...
>                      ---------
>                      |       |
>                    email     ns
> 
> In other words, a fairly typical small network.  I've got an 8-IP
> subnet; all hosts outside the NAT have real IPs:
> 
> router: 1.2.3.193
> firewall: 1.2.3.196  fxp0
>           1.2.3.197  fxp1
> nat:      1.2.3.198
> email:    1.2.3.194
> ns:       1.2.3.195
> 
> The problem I'm having is with my routing.  Surprise.  Here is
> the routing table for the firewall:
> 
> default                 1.2.3.193 fxp0
> 1.2.3.193               link#1 fxp0
> 1.2.3.192/29            link#2 fxp1
> 1.2.3.196               lo0
> 1.2.3.197               lo0
> 
> The gateway_enable (net.inet.ip.forwarding) is also enabled on
> the firewall.

with a *routing* firewall, like the one you are using, you must have two
different IP subnets, one for each physical interface (or else, the
kernel will not know which interface to use to send a packet).

In your case, you should use a "bridging" firewall, where ony one of the
ethernet interfaces has an IP address (you can then set up your firewall
in a "stealth" config, where it does not touch the TTL in the IP
packets)

	TfH

-- 
Thierry Herbelot


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