Subject: VPLS question on MAC address withdrawal

From: "Shah, Himanshu" <[email-masked]>
Date: Thu, 29 Dec 2005 16:19:19 -0500

Hope somebody can shed light on the following questions....

(1)
There are two mechanisms described - 
MAC address withdraw List TLV and empty MAC Address withdraw List TLV

cut-and-paste from draft.

6.2.2. Address Withdraw Message Containing MAC List TLV 
   
  The processing for MAC List TLV received in an Address Withdraw 
  Message is: 
   
  For each MAC address in the TLV: 
     - Remove the association between the MAC address and the AC or 
        PW over which this message is received 
   
  For a MAC Address Withdraw message with empty list: 
     - Remove all the MAC addresses associated with the VPLS 
        instance  (specified by the FEC TLV) except the MAC addresses 
        learned over the PW associated with this signaling session 
        over which the message was received 
   
  The scope of a MAC List TLV is the VPLS specified in the FEC TLV in 
  the MAC Address Withdraw Message.  The number of MAC addresses can 
  be deduced from the length field in the TLV. 

To simplify the problem, lets assume that for a given VPLS instance A there are only 5 MAC
addresses and one PW. In this case, for TCN-Triggererd MAC-address-withdrawal, sending
a list of 5 MAC address vs sending an empty list achieves opposite result. That is, sending 
explicit list will cause the receiver to remove all 5 addresses (lets assume that they all were
associated with sender). But by sending, empty MAC-address-withdrawal list, it will remove 
none.  However, the draft says,

In order to minimize the impact on LDP convergence time, when the 
  MAC list TLV contains a large number of MAC addresses, it may be 
  preferable to send a MAC address withdrawal message with an empty 
  list. 

(2)
Is MAC-Address-withdraw mechanism ever intended to be used for U-PW (user facing PW, MTU-S<->PErs)?
If so, how, when, implication of withdraw msg from N-PW (PE<->PE) to U-PW, etc needs to
be described.

regards,
himanshu

Himanshu Shah
Ciena Corp