Re: semi OT: default route

[Jason Opperisano <opie@817west.com>]

On Wed, Oct 20, 2004 at 05:37:34PM +0100, Nick Drage wrote:
> However if you want to give the routes different metrics....
> 
> ip route add default via 1.2.3.4 metric 1
> ip route add default via 4.5.6.7 metric 2
> 
> "ip" will accept that input.
> 
> That should mean if the host can't send the traffic via 1.2.3.4 it will
> realise this ( I presume solely if it gets no arp-reply for 1.2.3.4) it
> will try and send the traffic via 4.5.6.7 instead.
> 
> That seems to be the way it should work, however on a test box my host
> is happily trying to arp for 1.2.3.4 continuosly.
> 
> Anyone help me finish off this answer ;)

yes--the linux routing code will do dead gateway detection and fall
back to a lower metric route in the event of failure, and also go back
to the higher metric route upon resurrection.  this can be useful for
an active-standby setup.

as for which route added by 'route' actually gets used--i've never spent
the time to figure out how it picks the one it uses, but it certainly
only appears to ever use one--maybe it picks the one with the lowest
numerical value...  or maybe it uses one of those magic 8-ball things...

-j

-- 
Jason Opperisano <opie@817west.com>