Alcatel-Lucent 7210 SAS M Service Guide

VPLS Features
Page 278 7210 SAS M Services Guide
Redundant Access to VPLS Without STP
The Alcatel-Lucent implementation also alternative methods for providing a redundant access to
LAYER 2 services, such as MC-LAG, MC-APS or MC-RING. Also in this case, the topology
change event needs to be propagated into VPLS topology in order to provide fast convergence.
Figure 42 illustrates a dual-homed connection to VPLS service (PE-A, PE-B, PE-C, PE-D) and
operation in case of link failure (between PE-C and L2-B). Upon detection of a link failure PE-C
will send MAC-Address-Withdraw messages, which will indicate to all LDP peers that they
should flush all MAC addresses learned from PE-C. This will lead that to a broadcasting of
packets addressing affected hosts and re-learning process in case an alternative route exists.
Note that the message described here is different than the message described in previous section
and in RFC 4762, Virtual Private LAN Services Using LDP Signaling. The difference is in the
interpretation and action performed in the receiving PE. According to the standard definition, upon
receipt of a MAC withdraw message, all MAC addresses, except the ones learned from the source
PE, are flushed,
This section specifies that all MAC addresses learned from the source are flushed. This message
has been implemented as an LDP address message with vendor-specific type, length, value (TLV),
and is called the flush-mine message.
The advantage of this approach (as compared to RSTP based methods) is that only MAC-affected
addresses are flushed and not the full forwarding database. While this method does not provide a
mechanism to secure alternative loop-free topology, the convergence time is dependent on the
speed of the given CE device will open alternative link (L2-B switch in Figure 57) as well as on
the speed PE routers will flush their FDB.
In addition, this mechanism is effective only if PE and CE are directly connected (no hub or
bridge) as it reacts to physical failure of the link.

Alcatel-Lucent 7210 SAS M Specifications

General

Brand	Alcatel-Lucent
Model	7210 SAS M
Category	Switch
Language	English