Creative" Applications For H-Vpls; Figure 3: Traffic Sent N Time Over The Same Link Of The Ring - Juniper M10i Application Note

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APPLICATION NOTE - Demystifying H-VPLS

"Creative" Applications for H-VPLS

In addition to the previously described motivations for using H-VPLS, we are seeing how H-VPLS is being positioned

and used as the response to LDP VPLS Forwarding Plane "Achilles Heel": Handling multicast traffic (LDP VPLS

Control Plane "Achilles Heel" is the lack of auto-discovery).

It is well known that VPLS relies on the replication of traffic on the ingress PE to deliver the "multipoint" capability of

VPLS. This happens for L2 multicast traffic, L2 broadcast traffic, and unknown unicast traffic.

Even though from the service and end customer's perspective, the service is actually multipoint, the inherent point-

to-point nature of this scheme produces serious inefficiencies in the network. The worst case scenarios are the ring

topologies, as can be observed in the following diagram, where traffic may need to be replicated over the same link

as many times as nodes exist on the ring.

So based on these performance attributes, some vendors have found H-VPLS to be "the answer" for this VPLS

inefficiency.

Sometimes it is proposed that H-VPLS mechanisms be used to create "artificial" replication points on a VPLS-based

network such that it is possible to minimize the amount of ingress replications required to transport multicast traffic

over VPLS. The way to create this is by configuring these nodes as H-VPLS hubs, but making them interpret that the

device on the other end is an H-VPLS spoke, so effectively the split horizon rule is not applied, and traffic received on

a pseudowire is forwarded to the next replication point.

CPE

MAC table

LDP active psuedowire

LDP backup psuedowire

CPE

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