[Sussex] Persistent routes

[Simon Huggins]

On Tue, May 15, 2012 at 02:13:30PM +0100, Steve Dobson wrote:
> 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.

In practice you can only have one default route.

You can have many default routes but only one takes effect because as
you say it matches all addresses (the last one added IIRC).

If you want to route via two lines or to have a fallback you need
something else which detects that the link has failed and removes the
failing route which switches everything to the other route.

More normally as an ISP or if you were doing routing properly you'd do
BGP (external or internal) or OSPF or similar. i.e. use proper routing
software; you can do this on linux with quagga for instance.

Simon.

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