[AusNOG] steering inbound BGP (Telstra)

[Tony]

I've done this in the past (but don't claim to be an expert). Track a BGP prefix on one of the links and if it dissapears start advertising BGP routes on the alternate link. You may be wondering what stops the tracked prefix from appearing via the backup link and never going down, the answer was that the primary BGP provider was configured for "domestic routes" and the backup provider was configured for "default only" so that the only service the tracked /16 would appear from was the primary link.

From memory the reason for doing this was that the backup link was a lot smaller in comparison to the primary one, so was only to be used in the "emergency" situation (it was a DSL2 service backing up a 10M fibre, the backup link have also had a small per MB data allowance on it). Yes, it was a small customer with a single /24 (their own one from ages ago) and this is how they wanted it to work. They were aware of the failover times involved and were happy with this.

Many strange and bizarre things are possible if you think hard enough about how to do them. This doesn't always mean they are good things to do but as long as you don't bust anything feel free to be creative !


regards,
Tony.




________________________________
 From: Joshua D'Alton <joshua at railgun.com.au>
To: Chris Gibbs <Chris.Gibbs at gosford.nsw.gov.au> 
Cc: "AusNOG (AusNOG at lists.ausnog.net)" <AusNOG at lists.ausnog.net> 
Sent: Monday, 17 February 2014 1:15 PM
Subject: Re: [AusNOG] steering inbound BGP (Telstra)
 


I could be wrong but BGP just doesn't support what you're wanting, and even more so no carrier is ever really going to work in the way you describe. It should never make sense (for a carrier) to not prefer their own routes (which are directly connected, ie admin dist 1), vs those of their peers (even if settlement free, admin dist 1+N), even if communities were involved (i believe telstra do use communities internally between telstra/telstraglobal/reach).

Even if you advertised /24s telstra would still use their own learned routes (from you) rather than peer learned routes (from your alternate upstream), as designed BGP.

I don't know for sure it is default behaviour for TWI, but I believe it is default for... the internet in general.

I think the only way to achieve what you want would be to engineer the system such that nothing is advertised to telstra, and only advertised if the other link goes down. I can think of a few ways to do this, but keeping in mind BGP announce times, it wouldn't be a 100% uptime.

Good luck with the traffic engineering, there are definitely a few onlist that are experts.



On Mon, Feb 17, 2014 at 1:59 PM, Chris Gibbs <Chris.Gibbs at gosford.nsw.gov.au> wrote:

Hey all,
> 
>We currently utilise Telstra Internet Direct services for our primary inbound for AS38236, I would like to move to using Telstra as the least preferred and swap to another provider for inbound.
> 
>When I tested the swap, the majority of domestic looking glasses were confirming inbound through our preferred inbound. However Telstra always seems to prefer their own routes instead of peer learnt; even after setting either as-prepend or MED. A Telstra engineer confirmed this.
> 
>My question is pretty much is there any other way to steer inbound traffic to us through Telstra? (without grabbing a /23 and advertising more specific 2 x /24s or using communities, which Telstra doesn’t support)
> 
>The only other alternative would be to swap providers at our DR site, and we originally had issues getting a service installed there.
> 
>Does anyone also know if this is the default behaviour through Telstra Wholesale Internet?
> 
>Cheers ,
>   Chris Gibbs
>Network and Security Engineer | Information Management & Technology
>Gosford City Council
>(PO Box 21)
>Gosford NSW 2250
>P  (02) 43258888
>M  0408 222 496
>E  Chris.Gibbs at gosford.nsw.gov.au 
> 
>        gosford.nsw.gov.au   
> 
> 
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