Ken Hornstein writes:


[Andreas Wrede <andreas@planix.com> writes]

>>Paul Vixie published patches for BSD/OS 2.1 which allow for a default
>>route per interface and which remember the interface via which a tcp
>>connection was initiated. See ftp://ftp.vix.com/pub/vixie/ifdefault/
>>for more.

>Okay, I guess I'm just stupid this morning ... what are the gains in
>using this?  I have a multihomed machine at home, and I don't see how
>doing this would gain me anything.

Just from the description:
It lets you get away with a nontrivial local net (e.g., with multiple
distinct network numbers) on one side of a multihomed machine,
*without* running a real routing protocol :)

Think of a campus or neighbourhood cloud -- an Ethernet down the
street, say -- where all your neighbours have different IP addresses,
Or someone with multiple IP connectivity to their home, who wants to
do fail-over those links, wihtout running a routing protocol.

The places this trick fails should now be obvious: you're relying on
your neighbours to be smart enough to route *their* packets to *you*.
You just piggy-back replies out the interface their packets came in.
Can you say ``failure of the commons...''?

Maybe what's really meant here is routing on (src IP addr, dst IP
addr) rather than just destination address. Which is completely
different, though it can be used to similar effect.