Subject: RES: VPN/MPLS question

From: "Loureiro, Rodrigo" <[email-masked]>
Date: Thu, 5 Apr 2001 12:01:31 -0300

Yakov,

Thanks for the response. By the way, congratulations for all of the
materials that you have produced. 

>> Hi all,
>> 
>> Thinking about use EBGP sessions between the PE-CE connection, in order
to
>> insert customer's routing information into the VPN routing table and
provide
>> layer 3 redundancy for the customer's site using BGP, a scalability
problem
>> arises:
>> 
>> Once BGP has a loop avoidance mechanism based on the as-path vector, and
>> considering that i will not summarize the prefixes in the PEs, every site
>> participating in the VPN (peer) should have a different private
autonomous
>> system. 

>not necessarily. See Section 7 of draft-rosen-rfc2547bis-03.txt
>(and specifically text on page 5 of that document) for more on this.

OK, i have already read this RFC and i see three scenarios:

1) MPLS in the CE;

2) Redistribution in the CE/PE;

3) BGP-4 in the CE.

The network will be compound by many independent administrative sites
(different companies). All of the sites will be connected to two VPN/MPLS
service providers for redundancy, and the providers will be connected to
each other advertising the related (VPNs) prefixes.

Looking at the first scenario, i can see some problems. The first is that
the CEs will be "CPEs", i mean, small/medium capacity routers and should not
have support to MPLS. Also, this scenario will not scale regarding the
configuration environment. We are talking about a partial-mesh network with
hundreds of nodes and we don´t expect to mount an IBGP environment in the
network;

The second possibility is to use redistribution, once we can use the Site of
Origin loop avoidance mechanism. This scenario have a redundancy problem,
regarding routing convergence (ATM cloud);

The last scenario was the chosen one, but the scalability question arised
regarding the private numbers. 

Regards,
--

Rodrigo

---

From: Yakov Rekhter <[email-masked]>
Date: Thu, 05 Apr 2001 08:13:00 -0700

Rodrigo,

> materials that you have produced. 

Thanks !!!

> >> autonomous system. 

sorry for the typo - it should be "page 25 of that document".

> hundreds of nodes and we don't expect to mount an IBGP environment in the
> network;
> 
> Origin loop avoidance mechanism. 

That is the scenario I had in mind. Quoting from the Internet Draft:

         If a site is not in a transit VPN, note that it need not have a
         unique Autonomous System Number (ASN).  Every CE whose site
         which is not in a transit VPN can use the same ASN.  This can
         be chosen from the private ASN space, and it will be stripped
         out by the PE.  Routing loops are prevented by use of the Site
         of Origin Attribute (see below).

>                                  This scenario have a redundancy problem,

Could you elaborate more on this please.

Yakov.