How should multiple routers be handled by the client?

[Neff_Glen at emc.com]

This is really a TCP/IP question, and not so much a DHCP question.

"Default router" is actually a rather misleading term.  "Router of last resort" is actually a better description of its purpose.

Lots of configuration dialogs create the incorrect impression that "default router" is a per-interface setting, but it's really a per-host setting.  You can set multiple default routers, but since a default router is routing for the same block of IPs (0.0.0.0/0 (everything but the local network)), they're equal, ie. only the destination is different.  What this really means is that only the first one in the routing table order (netstat -rn) gets used.

-G


/*
 * Glen R. J. Neff
 * RTP TSG Lab Team
 * neff_glen at emc.com
 *
 * EMC^2 == E^2
 */



-----Original Message-----
From: dhcp-hackers-bounces+neff_glen=emc.com at lists.isc.org on behalf of Andrew Pollock
Sent: Tue 6/22/2010 10:57 AM
To: dhcp-hackers at lists.isc.org
Subject: How should multiple routers be handled by the client?
 
Hi,

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=586706, which I'm unable to
reproduce in my test environment with 3.1.3 or 4.1.1-P1, raises an
interesting question: how should the client configure the system if it
receives multiple IP addresses in the routers option?

Currently Debian appears to just add a default route for each IP address in
the order they're defined in the option, which seems to essentially mean
that the last one wins.

dhcp-options(5) just says that they should be listed in order of preference,
which to me says that Debian is currently doing it wrong, and we need to
iterate over the list of routers in reverse so that the first router wins.

regards

Andrew