Advertising the same IP block (with BGP) at multiple datacenters.

[optize]

Hi -

I have this IP block that I'm advertising via BGP to my providers.

I have two different datacenters, with two different providers.

My first datacenter is my primary datacenter and currently all the traffic goes there.

My second datacenter is my secondary datacenter and I have AS-PREPATH configured on that side of the BGP to add 10 (the most cisco allows) hops to that provider.

However, when I turn up that BGP on my second site, some traffic goes to it. Both datacenters are in the same city, I can't imagine the second datacenter is still the best route with the 10 AS-PREPENDS.

I can't have traffic go to that datacenter, unless the primary is down. Is there another way to accomplish this?

 

[jneiberger]

Welcome to the world of BGP. You can influence how traffic reaches your AS, but you don't control it. If your Internet connections were to the same provider, you would have more control. But since you're advertising those prefixes to separate providers, you're really at their mercy.

Some providers ignore AS path. You could try tweaking the metrics, but some providers ignore (or reset) those, as well.

 

[leedsit]

Hi,

Are you sure your backup site ISP is not stripping out your AS Path prepends. This is standard with some ISPs ( stripping out multiple same AS Paths ). Give them a shout to check / request that they dont remove these ( they should be able to change their policy or your neighbouring router). Im presuming you do have a ISP independant AS?

Lee

LEEroy
MCNE6,CCNP,CWNA,CCSA,Project+

 

[jneiberger]

It almost doesn't matter what they do, though. You never have complete control over how other ASes decide to reach your AS. If the backup site is advertising a route at all, there will be some traffic coming to it from time to time. That's almost guaranteed.

Is there a separate connection of some sort between the data centers? If so, perhaps you could configure some sort of conditional advertisement. If your Internet routers had a connection, you could set it up so that the backup site only advertises your prefixes if the main site goes down.