How do I set the source address on a multi-homed host?

Alin-Adrian Anton aanton at
Fri Feb 11 21:27:35 GMT 2005

Daniela wrote:
> I have two NICs (one inside and one outside interface) with NAT activated. The 
> problem is that every time I establish a connection with a machine on my LAN, 
> it uses the address of the outside interface as the source of the packets, 
> which creates problems with my firewall. How do I tell my machine to use the 
> other address whenever I connect to a local machine?
> Daniela

Hi Daniela,

Can you please be more specific? You mean this happens when you are 
connecting from inside intranet to some other point inside intranet?

I don't understand your topology. Intranet should have the same class 
network, C-class for instance /24, and the gateway should not see the 
packages from between 2 hosts in the same LAN. The switch/hub would see 
them only.

Can you please be more explicit of what's your setup, gateway rules, 
firewall, and what you are trying to do?

PS: if you are connecting from outside to inside, through the gateway 
which does nat, this sounds like bad firewall/nat rules.

Alin-Adrian Anton
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