On Wed, 2005-02-16 at 09:18 -0500, Scot L. Harris wrote: > On Wed, 2005-02-16 at 06:52, Bob Chiodini wrote: > > > > > Douglas, > > > > If you are strictly looking for redundancy then what you have done > > should work. If you want to specify a preferred router then take a look > > at the metric option to the route command. Lower numbers are more > > preferred. > > > > So how does the system use two default routes on the same subnet? Does > it send packets to both devices? If it does not then how does it decide > when to send packets to the second default route? > > > Also, if you can set up HSRP (Cisco-ish) of VRRP (IETF-ish) on the two > > I meant HSRP previously. :) > > > routers then you would only have one default router configured on each > > host and, the routers, through MAC address and IP address manipulation > > will take care of every thing else (IIRC). > > > > This is the only way I know for sure to provide redundancy for the > default router. > True HSRP and/or VRRP are ways to let the network guarantee that the default router is always available should there be failures. Some number of unique routers will appear as a single entity to individual hosts and will continue to route as long as all of the routers do not fail. The IP address assigned to the HSRP router is virtual and will physically reside on one of the redundant set. I think the routers can choose the best physical box to process the packets and depending on the configuration this physical router may vary over time and system load. I stand corrected. As to the metric option assigned to the default gateway, apparently it is not used by the kernel (man route). It looks like the kernel always picks the first default gateway in the table, whether it's up or not. However, a brief look at the kernel source, looks like if you compile the kernel with CONFIG_IP_ROUTE_MULTIPATH (2.6.10-1.766_FC3 was) you may be able to tweak what's happening to routing. http://lartc.org/howto/lartc.rpdb.multiple-links.html might provide some incite, and looks like what Douglas is trying to do. Bob...
