Routing issues

[dspazman at epicup.com]

Let's say you have two routing tables (T1, T2), one for each interface (eth0, eth1), so you can route traffic out each one separately.

https://git.nic.cz/redmine/projects/bird/wiki/BGP_example_2

I'm assuming there would have to be some changes to that BGP script to support both routing tables.  I'm not sure how to support multiple routing tables with bird.  Would someone be able to show that?  Seems like it would be a useful example in general, and be a pretty simple modification to that example for someone who knows what they are doing.

I didn't see anything on any of the examples on git.nic.cz that showed using multiple tables, as a configuration like http://lartc.org/howto/lartc.rpdb.multiple-links.html shows you'd be using for multiple outgoing connections, which you would typically have in a BGP situation.

Though maybe https://git.nic.cz/redmine/projects/bird/wiki/Policy_routing explains it.  I plan on keep looking into that example as well.

Thanks!


-----Original Message-----
From: "Martin Barry" <marty at supine.com>
Sent: Monday, December 5, 2011 11:53am
To: bird-users at atrey.karlin.mff.cuni.cz
Subject: Re: Routing issues

$quoted_author = "dspazman at epicup.com" ;
> 
> Would cause the path through the connection on eth0 to be 10x more
> prefered then the path through eth1, so incoming bandwidth should be split
> in about a 10-1 ratio.  So if I have eth0 as a 10 Gig connection, and eth1
> as a 1 Gig connection, between using that for incoming traffic, and a
> multipath rule for outgoing traffic like this:
> 
> ip route add default scope global nexthop via 1.1.1.153 dev eth0 weight 10 nexthop via 2.2.2.81 dev eth1 weight 1
> 
> Would cause the two connections to be pretty uniformly used on incoming
> and outgoing traffic at a 10/1 ratio, allowing me to pretty fully saturate
> both lines?

Like the other Martin said, this doesn't work quite how you are thinking.

BGP unfortunately has only a limited range of controls one can manipulate
and often you have no control over what remote ASes are doing and hence
can't control the inbound traffic as much as you would like (if at all).

You'll need to read up more on the BGP selection criteria and how these work
but the ones to focus on for...

Inbound
- prefix specificity
- AS path and prepending thereof
- Communities. Signals to your upstreams for things like 'no export' or
  prepending to specific ASes
- MED. This is works best with multiple links to the same provider.

Outbound
- filtering
- local preference


cheers
Marty