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

[Ted Mittelstaedt]

> -----Original Message-----
> From: owner-freebsd-questions at freebsd.org
> [mailto:owner-freebsd-questions at freebsd.org]On Behalf Of Daniela
> Sent: Tuesday, February 15, 2005 1:30 PM
> To: Jan Grant
> Cc: Alin-Adrian Anton; questions at freebsd.org
> Subject: Re: How do I set the source address on a multi-homed host?
> 
> 
> >
> > Having said that: technically, you specify source addresses for
> > connections by calling bind(2) prior to calling connect(2). 
> If you fail
> > to do this, the operating system will select a source IP address for
> > you. This'll often be the IP of the outgoing interface.
> 
> Well, if the OS selects the source IP, can't I just modify the 
> code that 
> selects it? Will this work all the time, or just when the 
> application lets 
> the OS select an address for it?
> 

Daniela,

  I have a FreeBSD 4 system setup as a NAT router, (it's real name is
nat-rtr.freebsd-corp-net-guide.com) that has 2 interfaces, the inside
is 192.168.1.1, the outside is 65.75.197.130

  This is in fact a real live system and I'm using it right now.

  I have several FreeBSD systems on the 192.168.1 network on the
inside, and several FreeBSD systems on the 65.75.197 network on the
outside.

  If I log into nat-rtr.freebsd-corp-net-guide.com (doesen't matter
what interface I connect to) and I initiate a Telnet session from
nat-rtr.freebsd-corp-net-guide.com to a system on the 192.168.1 network,
once I'm logged into that system, issuing a "w -n" command shows me
logged in from 192.168.1.1

  If on the other hand I log into a FreeBSD system that is on the
65.75.197 network, and issue a "w -n" command, then it shows me as
being logged in from 65.75.197.130

  If your setup isn't doing this, then it's screwed.  If it IS working
this way and you think there's something wrong, then it is you that
are screwed. :-)

  Could you confirm behavior one way or another - up until now the
explanations and your responses have been extremely fuzzy (open to
a number of different interpretations)

Ted