Re: [mpls] Comments on draft-ietf-mpls-ldp-multi-topology-01

[Lizhong Jin <[e-mail]>]

Hi,
I agree with Ice's summary. I don't think it is very difficult to choose
the option of signaling MT-ID within FEC.

Thanks
Lizhong




> ------------------------------
>
> Message: 2
> Date: Thu, 17 Nov 2011 23:34:50 +0800
> From: IJsbrand Wijnands <[e-mail]>
> To: Quintin Zhao <[e-mail]>
> Cc: [e-mail]
> Subject: [mpls] Comments on draft-ietf-mpls-ldp-multi-topology-01
> Message-ID: <[e-mail]>
> Content-Type: text/plain; charset=us-ascii
>
> Dear Quintin,
>
> During the MPLS WG presentation you asked for feedback on the different
> options to signal the MT-ID. See below;
>
> I've worked on this with Kamran Raza and we came to the conclusion there
> is really only one good option to signal the MT-ID, and that is within the
> FEC. This is true for LDP, and very much true for mLDP. We documented the
> preferred solution for mLDP, which would also apply to LDP. See;
>
> draft-iwijnand-mpls-mldp-multi-topology-00.txt
>
> Below is a summary of the reasons;
>
> - The LDP spec allows for multiple FEC's to be signaled in a single label
> mapping. If you don't add the MT-ID into the FEC its becomes difficult to
> match the MT-ID the right FEC, so you can't mix and match FEC elements, for
> example for IPv4 and IPv6. For the same reason Address Family is part of
> the FEC.
>
> - The MT-ID is something that is directly related to the Prefix/Root
> address encoded in the FEC, so it makes sense to combine them.
>
> - LDP messages and specifications that use FEC (e.g. Typed Wildcard,
> End-of-LIB) will automatically be extended for MT. There is no need to
> specify for which messages (map, withdraw, release etc..) the MT-ID applies.
>
> - If you are doing mLDP Live-Live using MTR (or MRT) and the 2 LSPs
> merge/overlap for some reason, you potentially duplicate the traffic and
> prevent live-live from working. For that reason the MT-ID MUST be in the
> FEC to make sure the 2 LSPs are unique and will never accidentally merge.
>
> - With mLDP a router may receive label mappings from multiple downstream
> routers, each of them including a different MT-ID. At that point you would
> need come up with some selection logic on which MT-ID you need to select
> and signal upstream. If the MT-ID is part of the FEC, you don't have that
> problem.
>
>
> Thx,
>
> Ice & Kamran
>
>
> ------------------------------
>
> _______________________________________________