Routing With Two ISPs?

Lars Eggert larse at ISI.EDU
Fri Nov 7 07:15:36 PST 2003


Helge Oldach wrote:

> Drew Tomlinson:
> 
>>I have a 4.8 box serving as a gateway with two connections to the
>>Internet.  Is there some way to set the box up so that packets are
>>routed out through the same interface from which they arrived?  For
>>example, if a connection is initiated on port 80 from a packet arriving
>>on one interface, is there a way to make the outgoing packets from my
>>web server use that same interface as a gateway instead of the default
>>interface?
> 
> 
> Unfortunately not. While your application (multi-homing, aka "strong ES"
> model of RFC 1122) would appear simpler, a general solution would target
> at true policy-based routing.

For some simple setups, you can use ipfw fwd rules to forward on 
something other than destination address.

But I agree that for more complex things you need some implementation of 
policy routing.

Lars
-- 
Lars Eggert <larse at isi.edu>           USC Information Sciences Institute
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