Subject: RES: RES: VPN/MPLS question

From: "Loureiro, Rodrigo" <[email-masked]>
Date: Thu, 5 Apr 2001 14:11:30 -0300

Yakov,

>> The second possibility is to use redistribution, once we can use the Site
of
>> 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).

>>2) Use static routing in the CE/PE, redistributing them into the VPN
routing table.
>>
>>                                  This scenario have a redundancy problem,
>> regarding routing convergence (ATM cloud);

>Could you elaborate more on this please.

OK. Regarding this approach we have two solutions:

1) Use BGP in the CE and a unique ASN for the whole network (VPNs), once it
will be stripped in the PE. This solution can solve the scalability problem.

2) Use static routing in the CE/PE, redistributing them into the VPN routing
table. As i said this solution has a redundancy problem. For this solution
to work properly, the PE should stop redistribute the CE prefix into the
VPN, once the IP connectivity between the PE/CE is not available anymore. If
we think about an ATM cloud, the PE probably will be connected to an ATM
switch, which creates a PVC through the ATM cloud till the access switch
(probably a frame-relay switch), which is connected to the CE. Now consider
that the physical link between the CE and the access switch went down. The
protocol in the interface connecting the CE to the switch will went down,
and the CE should converge correctly through the redundant interface
(considering that the CE automaticaly removes the routes from the routing
table). However, the PE is connected to an ATM switch through an ATM main
interface, and the connection to the CE was done through an ATM
subinterface. At this moment, the L2 protocol in the PE subinterface is
already up (once it´s directly connected to the ATM switch), so the static
route is already a valid entry in the PE routing table. This way the
redundancy doesn´t work.

Maybe should be possible to solve this problem using OAM cells, but, in
fact, we cannot count on this at this moment. What do you think?

Thanks,
--

Rodrigo