Subject: Reply to your comments on the draft "Optimized MAC Address Operations in VPLS with Redundancy"

From: Jiang Yuan-long <[email-masked]>
Date: Wed, 06 Aug 2008 17:34:01 +0800

Hi, Ali:

Thanks for your comments in the last L2VPN WG meeting, I will try to give you some reasons here.
Following are the two questions:

1. What do you think will be faster convergence? When you flush MAC addresses, 
the learning is done in data plane at wire speed. Why does that prolong convergence time?

-Faster convergence means the time to associate the MACs with the "exact" out port
will be shorter. Though learning is done in data plane at wire speed, the time for a frame to arrive 
at the end host and the response time for a host to send a reverse frame accross the PE (on which the 
MACs is flushed) will be a rather long time. So the learning process is not only determined solely by 
the wire speed, but also on the host processing time and delays on all the intermediate routers.
For this reason, flooding may also last for a rather long time.

2. You consider a simple case with simple backup for primary. In cases where primary fails and traffic gets
 distributed among multiple PE's, how do you take care of that?

-I believe the most commonly deployed scenario is one backup PE for a primary PE.
In my opinion, for the scenario of multiple backup PEs protecting a primary PE, 
only one PE out of them will be elected as the working PE when the primary PE failed, 
rather than distribute the traffic over multiple backup PEs,
otherwise, loops may be introduced to the attached customer site.
BTW, in a similar way, for PW redundancy mechanism, only 1 secondary is selected as the working PW (see 
draft-ietf-pwe3-redundancy-bit-00.txt in PWE3 WG)
Anyway, if there is any such requirements confirmed, I think it will be OK for us to find some solutions and 
add them to the future drafts. 

cheers,
Yuanlong