[Sussex] Persistent routes

Simon Story simon.story at catalyst-eu.net
Tue May 15 14:22:03 UTC 2012


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On 15/05/12 14:13, Steve Dobson wrote:
> Hi Simon

> Why can you have only one default route? As far as I am aware the
> default route is nothing special (in routing terms) other than it
> matches all addresses so it needs to be the last route tried by the
> routing software.  Therefore, a site with two ISP links would have
> two default routes and a packet could be routed via either to get
> off the site.  Useful if one of the links should go down or (more
> likely) become very busy.

The problem is that debian/ubuntu doesn't understand what you mean
when you specify 'gateway' twice. It just does something in the
background like:

'ip route add default via 192.168.23.254'

Which works 99% of the time.

And if you specify gateway again, it does that exactly the same thing,
only with a the new address you specified. And you'll see it refuses.
Have a go on a debian/ubuntu box.

That's not to say it's impossible, it is the debian interfaces file
runs out of steam for anything but a basic configuration.

To do anything more complicated, as the OP was attempting, one should
do 'up <blah>' in the interfaces file.
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