[c-nsp] Anycast//DNS - BGP

[cnsp at matthias-mueller.net]

Hi,

it isn't quite that easy. Never heard before about the diverse-path feature on Cisco for RRs, but looking at your link it looks like to have this probably limiting restriction in most setups:
'Path diversity is configured within an AS, within a single RR cluster. That is, the RR will advertise the diverse path to its RR client peers only.'

In case you have one RR cluster per datacenter and multiple DNS anycast servers per datacenter, only the best path per datacenter will be distributed to the iBGP full-mesh and only the local DC routers will know about local multiple paths. In case the backbone routers connected to the DC can directly reach all DC routers, only one of the DNS anycast servers will be contacted (assuming the anycast servers are connected to different DC distribution routers). So no traffic balancing will happen for traffic comming from your backbone-routers (part of the full mesh).

If you use a global RR cluster for all datacenters, even traffic distribution accross severall datacenters won't happen if your setup includes full-meshed iBGP peers.

So it's not only turning that feature on on your RRs, but you'll have to consider how your RR-clusters are setup and how they are placed in your topology (for anycast it is more or less the same like trying to get BGP based multipathing to work in a RR environment).

Or did I miss something?

Cheers,
Matthias

On Fri, 04 May 2012 17:47:39 +0200
Robert Raszuk <robert at raszuk.net> wrote:

> Hi Henry,
> 
>  > Currently we have issues with the RR (Only select the main route)
> 
> That's an easy one to solve :)
> 
> Try using either add-paths or diverse-path on the RR. The latter is much 
> easier as it does not require upgrade of all of your BGP speakers !
> 
> http://goo.gl/KDjlg
> 
> Best,
> R.
> 
> > We want to work with DNS that are span geographical. Our DNS have the same IP.
> > We need to configure the Backbone IP (BGP) to distribute this IP (Anycast).
> > Could you have any examples over how to deployment Anycast?
> > Currently we have issues with the RR (Only select the main route)
> >
> > Thanks a lot!
> >
> > Henry
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