BGP - draft-ietf-idr-bgp-optimal-route-reflection-19

[Ondrej Zajicek]

On Sat, Nov 02, 2019 at 05:41:34PM +0200, Philippe Duke wrote:
> Hello,
> 
> Does someone has an effort to implement 
> draft-ietf-idr-bgp-optimal-route-reflection-19 for BGP?
> 
> I see there is a difficulty in 4.1 in IGP metric. As far as I know, most
> of vendors are currently using IGP approach .
> 
> How can I get IGP an abstract metric for peer address?
> 
> I see the need to implement BGP-LS first before. It will allow
> separation of protocols and more.
> 
> Having BGP-LS stub code would help in implementation of other features.

Hello

I thought about ORR several weeks ago. The draft is pretty fuzzy about how
to get IGP metrics, but it seems it is understood it is done by BGP-LS.

I see three possibilities:

1. BGP-LS, that is interesting idea, but plenty of work. Perhaps later.

2. Just make GRE tunnels from routers to RR and run multiple IGP (OSPF)
instances on RR, each for every router /  GRE tunnel. That would have
a higher overhead than (1), but can be done with almost no modifications
to current BIRD.

3. Just propagated computed IGP routes (including metrics) from router to
RR using BGP, perhaps in separate BGP session to avoid mixing them with
'real' BGP routes. Unfortunately regular BGP does not offer native way to
attach IGP metric to a route, but one can use AIGP attribute for that or
just abuse some other existing attribute (e.g. LOCAL_PREF) with some
filtering code.

Both variants (2) and (3) can be easily implemented in BIRD with minimal
changes, with configuration similar to multitable RS setup. The only
thing that has to be added is filter ability to change table in which
BGP next hop (and IGP metric) is recursively resolved.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."