Subject: BPDU snooping in multihoming VPLS

From: Xu Xiaohu <[email-masked]>
Date: Thu, 27 Mar 2008 16:05:46 +0100

Hi All,

In section 5.1 of draft-ietf-l2vpn-vpls-bridge-interop-02.txt, there are two
methods of propagating the CCN message over the VPLS network. The first
method is to translate the in-band CCN message into an out-of-band "MAC
Address Withdrawal" message as specified in [VPLS-LDP] and the second method
is to treat the CCN message as customer data and pass it transparently over
the set of PWs associated with that VPLS instance.

In the former method, it requires the receiving PE to translate the "MAC
Address Withdrawal" message into CCN message reversely and send it to its
local CE (switch) via its AC interfaces. In the latter method, it requires
the snooping should be enabled both on the AC interfaces and on the PW
interfaces.

I wonder whether we could integrate the two methods mentioned above as
follows: The BPDU of C-network will be passed transparently in the VPLS
instance, while BPDU snooping is enabled and only enabled on the AC
interface. Upon receiving the TCN, the PE will flush all the MAC addressed
learned for the related VSI and send "MAC Address Withdrawal" message to the
other PE neighbors of the related VSI. 

Any comment welcomed!

Best wishes,
Xiaohu XU

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   5.1.  Customer Network Topology Changes 
    
   A single CE or a customer network can be connected to a provider 
   network using more than one User-Network Interface (UNI). 
   Furthermore, a single CE or a customer network can be connected to 
   more than one provider network. [RFC-4665] provides some examples of 
   such customer network connectivity that are depicted in the figure 
   below. Such network topologies are designed to protect against the 
   failure or removal of network components with the customer network 
   and it is assumed that the customer leverages the spanning tree 
   protocol to protect against these cases. Therefore, in such 
   scenarios, it is important to flush customer MAC addresses in the 
   provider network upon the customer topology change to avoid black 
   holing of customer frames.  
 .....   
   [P802.1ad] requires that customer topology
   change notification to be detected at the ingress of the S-VLAN
   bridge component and the S-VLAN bridge transmits a Customer Change
   Notification (CCN) BPDU tagged with the S-VLAN ID associated with
   that service instance and a destination MAC address as specified in
   the block of 16 reserved multicast MAC addresses. Upon receiving the
   CCN, the provider bridge will flush all the customer MAC addresses
   associated with that S-VLAN ID on all the provider bridge interfaces
   except the one that the CCN message is received from.
   
   Based on the provider bridge model depicted in figure (1), there are
   two methods of propagating the CCN message over the VPLS network.
   The first method is to translate the in-band CCN message into an
   out-of-band "MAC Address Withdrawal" message as specified in [VPLS-
   LDP] and the second method is to treat the CCN message as customer
   data and pass it transparently over the set of PWs associated with   
   that VPLS instance. The second method is recommended because of ease
   of interoperability between the bridge and the LAN emulation modules
   of the PE.
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