Re: [OSPF] draft-ietf-ccamp-automesh-01.txt

[Kireeti Kompella <kireeti@juniper.net>]

Hi Adrian,

On Sat, 13 May 2006, Adrian Farrel wrote:

> There is a draft in CCAMP that I want to bounce off the OSPF working group.
...
> My questions to you:
> 1. Is it a concern that P-routers are being used to store and forward
>  opaque information only needed by a small subset of the routers
>  in the network?

Necessary evil (i.e., No; see below)

(I would reconsider the use of the word "small" -- in most networks I 
have seen, the number of PE routers vastly outnumber the number of P 
routers.)

> 2. Is there a scaling concern that there is no control on the number of
>  mesh groups that may exist, nor the number of mesh groups to
>  which any router can belong?

I guess an implementation could go berserk and advertise 65536 bytes 
worth of mesh groups, but no, this doesn't concern me too much.

> Context:
> This question arises in the context of 
> draft-bryskin-l1vpn-ospf-auto-discovery-01.txt that is being discussed in the 
> L1VPN working group. This I-D proposes to use the IGPs (specifically OSPF) to 
> distribute information about which VPNs can be accessed through the PEs (not 
> general VPN membership or reachability information, but just a list of VPN 
> IDs and the link I-Ds that are used to reach them). Loud voices have been 
> raised in L1VPN about the scalability and appropriateness of such an idea, 
> and since it seems to be very similar to automesh, I want to see whether you 
> all think there is a problem with automesh.

I have the same issues with using ISIS/OSPF for auto-mesh as I do for 
autodiscovery in L1VPNs -- OSPF and ISIS are not ideal vehicles for 
such information.  However, there are two very important differences 
in these two cases:

1) BGP is often not present on "interior" routers (consider the case
   of "P" routers fully meshed with TE LSPs, and PEs running LDP; and
   BGP running only on PEs -- "BGP-free core")

2) It is vital for VPNs that a good policy mechanism be available to
   control the distribution of information -- otherwise, there could
   be serious breaches of privacy.

That said, I would like to see automesh information carried in BGP, 
to be used in preference to ISIS/OSPF whenever possible.

Kireeti.
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