Multiple default routes on multihome host

[Bruce M. Simpson]

Nick Barnes wrote:
> I want packets from address A1 to be sent via gateway G1, but packets
> from address A2 to be sent via gateway G2.
>
> How do I do this?  Can I just have more than one default route?  I'm
> remote from the machine in question, so I don't want to tinker with
> the default route until I'm sure of the answer.
>   

Others have chimed in saying that having redundant routes constitutes 
poor network design: it really depends where one draws the distinction 
between router and host. In ad-hoc and peer-to-peer networks, there is 
no such distinction.

The forwarding code doesn't support multiple routes to the same 
destination, largely out of development inertia. People are looking at 
this now.

The forwarding code doesn't support load balancing yet, it's being 
considered for the future. There are problems with load balancing and 
TCP as it can result in loss of the original packet ordering. Of course 
this is something which stuff like SACK *begins* to address, it is a 
scenario more common in satellite networks.

However you want next-hop selection based on the "laddr" for a socket 
which is a different thing. The stack doesn't do this on its own, it 
needs help from packet filtering code.

You should be able to achieve this using "route-to" rules in IPFW or PF, 
there are tutorials out there on the subject.

cheers
BMS