[c-nsp] IOS XR / advertise best-external

[Dan Peachey]

On 19 May 2015 7:54 am, "Adam Vitkovsky" <Adam.Vitkovsky at gamma.co.uk> wrote:
>
> > Dan Peachey
> > Sent: 18 May 2015 22:04
>
> >
> > On 18 May 2015 9:40 pm, "Gert Doering" <gert at greenie.muc.de> wrote:
> > >
> > > Hi,
> > >
> > > On Mon, May 18, 2015 at 09:23:50PM +0100, Dan Peachey wrote:
> > > > If that's the case I find it strange why that's now the default
> > behaviour.
> > > > Surely that's the point of 'additional-paths' to control what
routes you
> > > > want to have backups for. In my case I definitely wouldn't have
wanted
> > > > backup routes for everything by default.
> > >
> > > BGP add-path is for sending multiple routes for a single prefix
towards a
> > > BGP peer. Different thing again...
> > >
> > > gert
> >
> > You can use 'additional-paths selection' on its own without 'send' or
> > 'receive' to filter what backup routes you install in the RIB/FIB. Using
> > this on its own does not negotiate add-path with any peers or advertise
> > multiple routes.
> >
> > Unless I missed the point, the default behaviour of enabling
> > 'best-external' now seems to be to install the backup route in the
RIB/FIB,
> > which was not the case last time I looked at it and may not be desired
> > behaviour.
> >
> > Regards,
> >
> > Dan
> >
>
> I'm pretty sure that even on 4.3.4 for eBGP prefixes you need to use the
"additional-paths selection route-policy" to get a backup route installed.
> Though I'm not that sure/can't recall what the behaviour was for iBGP
prefixes, though flooding FIB with all the backup routes is certainly not
desirable.
>
> adam
>

I was using 4.3.4 SP1 and "additional-paths selection route-policy" was
required to install eBGP/iBGP backup routes, which is fine by me and make
sense. But now it appears that the default is to install the backup route,
unless it's actually a bug...

Dan