Subject: RE: [L1vpn] Autodiscovery Protocol

From: "MEURIC Julien RD-CORE-LAN" <[email-masked]>
Date: Thu, 23 Mar 2006 18:49:27 +0100

Hi Igor.

I am glad to see L1VPN discussions are back on the air. :-)

Please, see below.

-----Original Message-----
From: Igor Bryskin [mailto:[email-masked]] 

Julien,

Thanks for the comments. Please, see in-line.

Igoe

----- Original Message ----- 
From: "MEURIC Julien RD-CORE-LAN" <[email-masked]>

Hi all.

Allow me to get back to the issue raised during the L1VPN meeting: the
autodiscovery protocol.

I think it is clear for everyone that BGP really fits the job. Thus I do not
see why we would need to add an IGP to do less things. Lots of drawbacks
were even pinpointed during the meeting: more flooding, less scalability, no
AS crossing, less flexibility (full mesh)... but no real advantage.

IB>> Just a couple. 1) No need for BGP. Untill now operators of L1 layer
networks don't seem to find any use for BGP, and unlikely to deploy BGP for
the purpose of one application some time soon

[JM] OK, but BGP is already deployed for this over some networks other than L1. Autodiscovery is not L1 specific and I do not see the need to introduce too specific mecanims when it is not necessary to be so specific. As soon as we have started to deploy a whole IETF artillery (IP + LMP + OSPF/IS-IS + RSVP-TE + ...) to introduce a CP into transport networks, I feel that we should use already well known bricks too build the wall, and avoid to fill gaps with (ad-hoc) half bricks.
Moreover, I believe that multi-AS is a key feature to support.

2) IGP solution facilitates
easier integration with TE, which is very important for GMPLS based control
plane

[JM] I must concede this.

What is more, as Kireeti said, starting with 2 different solutions is likely
to bring more problems than solve any. Since something needs to be added, I
am not sure that extending an IGP (or both if we do not want to preclude any
option...) will be easier/quicker than using BGP.

IB>> As was pointed out on the meeting, this is not an argument of a sort
RSVP-TE vs CR-LDP. The architecture (basic mode) clearly assumes the
protocol independence of L1VPN auto-discovey mechanism. The OSPF extensions
are very simple, the application is required now and based on OSPF could be
delivered quickly. What happens if the BGP solution proves to be a better
one (as it happened in the past) ?
Than the OSPF solution could be simply thrown away and replaced by the BGP
one.

[JM] I agree with the scenario, but this introduces another issue which is migration, and that is not the easiest part. Furthermore, we are not in the position where we think about extending IGPs until a new solutions shows up: BGP already exsits, and the draft was ready even before.

Cheers,

Julien

Igor

 And if, despite this, some consider it as a 1st step, then I think we do
not need to make it a standard.

So I am in favour of BGP autodiscovery, but BGP only.

Best regards,

Julien

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---

From: "Igor Bryskin" <[email-masked]>
Date: Thu, 23 Mar 2006 15:07:55 -0500

Hi Julien,

I really like the discussion. It has already produced some very good
results.

Please, see in-line.

Igor

----- Original Message ----- 

Hi all.

[JM] OK, but BGP is already deployed for this over some networks other than
L1. Autodiscovery is not L1 specific and I do not see the need to introduce
too specific mecanims when it is not necessary to be so specific. As soon as
we have started to deploy a whole IETF artillery (IP + LMP + OSPF/IS-IS +
RSVP-TE + ...) to introduce a CP into transport networks,

[IB] We are not talking about whole IETF artillery here. We are talking
about tiny OSPF extensions, very similar to what are currently working in
any GMPLS controlled network

I feel that we should use already well known bricks too build the wall, and
avoid to fill gaps with (ad-hoc) half bricks.
Moreover, I believe that multi-AS is a key feature to support.

[IB] I really would like to have a multi-AS L1 network operator as a
customer of Movaz :=) However,  I am yet to see a multi-area L1 network. You
have mentioned interop issues between the two solutions and inconvenience
supporting them both, and I am afraid you are missing a point here. In IP
network BGP and OSPF work together just fine - they both populate the same
RIB. How is it different from populating the PIT, which what L1VPN
auto-discovery is all about?
It certainly could be populated from many sources - BGP, OSPF,
configuration, etc. I don't see any issues for working the two mechanisms
simultaneously in the same (say, multi-AS) network. Would you disagree with
that?

[JM] I agree with the scenario, but this introduces another issue which is
migration, and that is not the easiest part.

[IB] Please, see my comment above

 Furthermore, we are not in the position where we think about extending IGPs
until a new solutions shows up: BGP already exsits, and the draft was ready
even before.

[IB] Well, the OSPF extensions would probably take 1 month to implement
(including extensive testing) and, as was said before, even basic BGP is not
deployed on L1 network

Two more points:

1) Scalability concerns. True, Ps do not need to have anything to do with
VPN information, and in OSPF solution they still need to participate in
flooding of L1VPN LSAs. However, OSPF is designed to distribute and manage
large numbers of external routes (AS-scope type LSAs). We do not need
external routes in L1 network - that's why we do not use BGP in L1 network
in the first place. Distribution of AS-scope L1VPN LSAs carrying VPN info
seems to be far smaller and far less dynamic substitution for type 5 LSAs

2) If IGP based discovery is such a bad thing, why don't we do discovery of
any type via BGP? For instance, there are reasons why we are doing, say, PCE
capabilities discovery via IGP. Why L1VPN discovery is any different ?

Igor