When VPLS services are used to connect routers, the service scales adequately,
but when VPLS is used to connect Ethernet switches, the number of MAC
addresses the PE device has to learn imposes a severe scaling limitation.
EoMPLS Shortcomings Ethernet pseudowires provide a simple point-to-point service
and have no intrinsic shortcomings, other than the inability of the PE to signal VLAN
MPLS 459
failures to the CE (as discussed previously in ???Pseudowire OAM???). VPLS services, however,
have specific shortcomings resulting from the VPLS architecture:
Mesh Failures The VPLS architecture assumes that all PE devices are fully meshed
over Ethernet pseudowires. If any pseudowire breaks (for example, because of LSP
failure), then the VPLS service no longer offers full connectivity between all attached
devices. This can cause severe issues with IP routing protocols that rely on multicast
to transport network reachability information.
Multicast Efficiency The EoMPLS architecture is designed to hide per-pseudowire
state from the core of the network to improve scalability. In multicast networks, there
is an inevitable tradeoff between core state and replication efficiency.
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