Subject: RE: [mpls] Question regarding MAC Withdrawal in H-VPLS Dual-homed MTU-s

From: "Dutta, Pranjal" <[email-masked]>
Date: Tue, 26 Sep 2006 15:22:06 +0530

Asaf,

           Please refer my answers inline.

Thanks,

Pranjal

________________________________

From: Asaf Henig [mailto:[email-masked]] 
Sent: Tuesday, 26 September, 2006 1:42 PM
To: [email-masked]; [email-masked]; [email-masked]
Subject: [mpls] Question regarding MAC Withdrawal in H-VPLS Dual-homed
MTU-s

It is yet unclear from draft
http://www.ietf.org/internet-drafts/draft-ietf-l2vpn-vpls-ldp-09.txt who
is responsible to send the MAC Withdrawal message to the secondary PE-rs
when fail-over occures in an H-VPLS dual homed MTU-s scenario.

Section 10.2.2 in the draft recommends that PE3-rs (in Figure.5 in the
draft) which is secondary PE-rs may

send out a flush message.  Secondary PE-rs is agnostic of switchover
events at MTU-s.  As MTU-s controls VC switchover so MAC address
withdrawal should be initiated by MTU-s.

It is known that when a primary VC fails in a dual-homing scenario the
PE-rs connected to the secondary VC should relearn the MAC addresses
behind the MTU-s. In order to make this process faster this "secondary"
PE-rs should flush the relevant previously learned MAC addresses. For
that to happen we have two options:
  
A) The primary PE-rs would send the MAC Withdrawal message to the
secondary PE-rs (and all other PE-s) the minute it recognizes that its
VC has failed.

Primary PE-rs shouldn't initiate MAC withdrawal on VC failure. Think
about a case when primary VC from MTU-s fails and secondary VC from
MTU-s to the secondary PE-rs is also down. In that case anyway traffic
from MTU-s won't get re-learned by secondary PE-rs and/or other PEs. So
the traffic will be permanently black holed and initiating MAC withdraw
by primary PE-rs is not necessary. So the MAC withdraw is sent only when
secondary VC is made active at MTU-s. MTU-s initiates MAC withdraw as it
is the device that decides switching over to secondary VC.

B) The MTU-s itself would send the MAC Withdrawal to the secondary PE-rs
the minute it switches from primary to secondary VC. The secondary PE-rs
would be responsible to propegate this message to all other PEs in the
VPLS domain (this option is recommended by
draft-pdutta-l2vpn-vpls-ldp-mac-opt-00.txt).

In this draft we have extended the MAC withdraw method recommended by
VPLS-LDP draft. We have kept provisions for both MTU-s initiated MAC
withdraw as well as PE-rs initiated MAC withdraw in the extension. There
could be other applications/scenarios of MAC withdraw where PE-rs may
need to trigger withdrawal. 

The 01 version is available at:
http://tools.ietf.org/wg/l2vpn/draft-pdutta-l2vpn-vpls-ldp-mac-opt-01.tx
t

Which option is preferred?

Thanks for any help.  
Asaf Henig
MRV communications