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

[Dan Peachey]

On 18 May 2015 7:21 am, "Marian Ďurkovič" <md at bts.sk> wrote:
>
> On Sun, 17 May 2015 13:48:42 +0200, Gert Doering wrote
> > RP/0/RSP0/CPU0:Cisco-F-X#sh cef  194.97.129.1
> > Sat May 16 23:26:20.777 MEDST
> > 194.97.129.1/32, version 76418887, internal 0x14000001 (ptr 0xa1045a14)
> >  [1], 0x0 (0x0), 0x0 (0x0)
> >  Updated May  9 14:43:16.617 Prefix Len 32, traffic index 0,
> > precedence n/a, priority 4 BGP Attribute: id: 0xc4eb, Local id: 0xbc96,
> >  Origin AS: 65300, Next Hop AS: 65300
> >
> >    via 10.10.11.45, 5 dependencies, recursive [flags 0x6000]
> >     path-idx 0 [0x9eac8c88 0x0]    next hop 10.10.11.45 via
10.10.11.45/32
> >    via 10.10.11.241, 5 dependencies, recursive, bgp-ext, bgp-best-ext
[flags
> 0x6060]
> >     path-idx 1 [0x9e5a92c0 0x0]    next hop 10.10.11.241 via
10.10.11.241/32
> >
> > ... and indeed, it nicely load-shares packets between the primary
> > service instance (behind 10.10.11.45) and the secondary service instance
> > (on the base IP 10.10.11.241).
>
> Hi Gert,
>
> the fact that both entries are present in RIB and CEF tables is expected
> behaviour. It's part of the new design, where both active and backup
paths are
> preinstalled into the CEF table, which allows much faster convergence
when the
> active path disappears. Note that the backup path has different CEF
flags, which
> should instruct the forwarding engine *not* to use it when another
regular path
> is present in CEF table.

Hi,

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.

Regards,

Dan