Service-delimiting VLAN tags will be removed before sending to
raw mode pseudowires and may be added when sending to tagged mode pseudowires.
When a frame arrives from a VPLS pseudowire, the PE strips the PW label and
uses it to identify the VPLS instance and the sending PE. The PE then learns the
source address of the Ethernet frame encapsulated in the pseudowire packet and, if
needed, adds it to the VPLS FIB. The PE then looks up the destination MAC address
in the FIB. If the MAC is known and corresponds to a local attachment circuit, then
the PE forwards the frame on that attachment circuit. If the MAC is unknown (or is
broadcast or multicast), then the PE replicates the packet and sends a copy to each
MPLS 445
local attachment circuit. VLAN tags may again be added or removed at this stage on
a per-attachment circuit basis.
VPLS Signalling As already discussed, VPLS signalling is simply an extended version
of pseudowire signalling. Each VPLS PE establishes an Ethernet pseudowire to each of
the other PEs in the VPLS. A unique PW label is assigned to each peer PE to enable the
local PE to identify the source of packets received over a PW.
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