Subject: draft-ietf-ccamp-automesh-01.txt

From: "Adrian Farrel" <[email-masked]>
Date: Sat, 13 May 2006 15:25:48 +0100

Hi,

There is a draft in CCAMP that I want to bounce off the OSPF working group.

draft-ietf-ccamp-automesh-01.txt uses the new opaque LSA defined in 
draft-ietf-ospf-cap-08.txt in order to carry information about "mesh 
groups". Members of mesh groups would be connected together by tunnels to 
provide a sub-mesh across the network.

There are many applicabilities of this feature, but it is wanted in CCAMP to 
allow the construction of a mesh of MPLS-TE tunnels between a set of MPLS 
label switching routers (LSRs) within the network. This set might be a 
sub-set of the PEs, or might be a sub-set of the P-routers used to build a 
hierarchical network.

The management of the mesh membership information is not the responsibility 
of the IGP. Rather, this is opaque information that is delivered to an 
application. Thus, SPF is acting as a transport for routing-related 
information.

Any router may be a member of more than one mesh group, and many routers 
might not be in any mesh group (consider the PE mesh case where all 
P-routers are not in the 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?
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?

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.

many thanks,
Adrian

---

From: Kireeti Kompella <[email-masked]>
Date: Mon, 15 May 2006 07:12:14 -0700 (PDT)

Hi Adrian,

> There is a draft in CCAMP that I want to bounce off the OSPF working group.
...
>  opaque information only needed by a small subset of the routers

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.)

>  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.

> 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.
-------

---

From: "Igor Bryskin" <[email-masked]>
Date: Mon, 15 May 2006 11:42:58 -0400

Kireeti,

Good to hear from you.

Please, see in-line.

Igor

----- Original Message ----- 
From: "Kireeti Kompella" <[email-masked]>
To: "Adrian Farrel" <[email-masked]>
Cc: <[email-masked]>; <[email-masked]>
Sent: Monday, May 15, 2006 10:12 AM
Subject: Re: [OSPF] draft-ietf-ccamp-automesh-01.txt

> have seen, the number of PE routers vastly outnumber the number of P

IB>> I think it is even more true in the context of L1 networks which in
most of the cases are bunch of interconnected rings of PEs with zero or very
few Ps.

>     be serious breaches of privacy.

IB>> Note, that what we are suggesting to advertise in L1VPN opaque LSAs are
locally configured CE-PE links and their association with VPNs. I am sure
that I am missing something, so could you help me understand:
a) what scenarios of "serious breaches of privacy" you have in mind?
b) how the BGP approach can help in this regard?

Thanks,
Igor