RE: BGP advertise-best-external on RR

["Jakob Heitz (jheitz)" <jheitz () cisco com>]

If your network is such that only a handful of routers supply redundant paths, then you can set up iBGP sessions with 
those directly without going via route reflectors. You can have most routes going through reflectors and a few through 
direct BGP sessions. Not everything needs to go through route reflectors. You can even do both: Have a router peer with 
a reflector as well as directly if you only need the redundant routes in a few places. You will end up with duplicate 
routes, but that's not a show stopper. You can avoid duplicate routes with route maps. You can have multiple route 
reflectors with different cluster IDs that carry the redundant routes only. Clients can peer with multiple clusters. 
Use route maps to avoid duplicate routes. These last things get complicated to manage, so I'd still go for add-path if 
at all possible.

--Jakob


> Message: 2
> Date: Tue, 1 Sep 2015 14:51:27 +0200
> From: Mohamed Kamal <mkamal () noor net>
> To: Jeff Tantsura <jeff.tantsura () ericsson com>, Diptanshu Singh
>       <diptanshu.singh () gmail com>
> Cc: NANOG <nanog () nanog org>
> Subject: Re: BGP advertise-best-external on RR
> Message-ID: <55E59F4F.8010704 () noor net>
> Content-Type: text/plain; charset=windows-1252; format=flowed
>
> Hi,
>
> Diverse-path will only send the second best path, and in my case I have
> three routes not two. In addition to that, every PE will have to peer
> with the RR via a second session (on the same RR, as I will not deploy a
> new standalone shadow RR) and this will increase the BGP sessions to the
> double.
>
> Add-path will have a network-wide IOS upgrade for this BGP capability to
> be supported which is not viable now.
>
> So, is there any other recommendation other than the internet VRF with
> different RDs solution?
>
> Regards,
>
> Mohamed Kamal
> Core Network Sr. Engineer
>
> On 8/25/2015 11:37 AM, Jeff Tantsura wrote:
> > Hi,
> >
> > In your case I?d recommend to use diverse path, due to its simplicity and
> > non disruptive deployment characteristics.
> > As you know - diverse path requires additional BGP session per additional
> > (second, next, etc) path, in most cases not a problem, however mileage
> > might vary.
> >
> > To my memory, in Cisco land - it has only been implemented in IOS, not XR,
> > please check.
> >
> > Cheers,
> > Jeff
> >
> >
> >
> >
> > -----Original Message-----
> > From: Diptanshu Singh <diptanshu.singh () gmail com>
> > Date: Monday, August 24, 2015 at 10:53 PM
> > To: Mohamed Kamal <mkamal () noor net>
> > Cc: "nanog () nanog org" <nanog () nanog org>
> > Subject: Re: BGP advertise-best-external on RR
> >
> > > Yes . In the case of diverse path , shadow route reflector will be the
> > > one wherever  you enable commands to trigger diverse path computation.
> > >
> > > Good thing with diverse path is that the RR-Clients don't have to have
> > > any support but bad thing is that it can only reflect One additional
> > > best-path( second best path ) .
> > >
> > > Sent from my iPhone
> > >
> > > > On Aug 24, 2015, at 2:31 PM, Mohamed Kamal <mkamal () noor net> wrote:
> > > >
> > > > It's only supported on the 15.2(4)S and later not the SRE train. I
> > > > might consider an upgrade.
> > > >
> > > > One more question regarding this, can you configure the RR to be the
> > > > main and shadow RR?
> > > >
> > > > Mohamed Kamal
> > > > Core Network Sr. Engineer
> > > >
> > > > > On 8/24/2015 9:16 PM, Diptanshu Singh wrote:
> > > > > BGP Add-Path might be your friend . You can look at diverse-path as
> > > > > well .