[AusNOG] steering inbound BGP (Telstra)

[Matthew Moyle-Croft]

On 16 Feb 2014, at 8:26 pm, Ben <ben at meh.net.nz> wrote:

> On Sun, Feb 16, 2014 at 08:12:15PM -0800, Matthew Moyle-Croft wrote:
>> 
>> On 16 Feb 2014, at 8:09 pm, Joshua D'Alton <joshua at railgun.com.au> wrote:
>> 
>>> Whoops completely forgot about localpref!
>>> 
>>> @Andrew  2x24/s wouldn't work for Telstra inbound though as they'd still be preferring their learned /23 from their customer vs the 2x/24s from their peer(s), right? Or do you mean it would work for making the majority of the traffic come in via the other provider?
>> 
>> Yes it would - /24s are more specific so preferred.  /23 would only kick in if /24s stopped being advertised.
> 
> Although that may work, I wouldn't advocate it without fallback routes.

"Fallback routes"?

More specifics are a common tool used to TE traffic.  The issue is if your /24s aren't globally advertised.  

> 
> What happens if Telstra receive traffic internationally from a peer on your advertised / 23?

This would only happen if that peer didn't have the 2x/24s as well.  Unless you're deliberately sending communities to prevent your other transit providers leaking the /24s I don't see much chance of it these days.

> 
> It comes into their network, and they have to do something with it.  Either they have a limited
> set of routes of their customer routes in that network, or they have a full BGP table.

Telstra have a full table, so they'd punt it via where THEY see the /24s.   You're a customer so unlikely to have BCP38 filter issues when the packets try and leave to goto your other provider.

The main issue is - if your other provider(s) don't have good domestic Australian connectivity, but again, I kind of assume anyone doing this has some clue and/or deserves some failure based learning.

MMC