Note that the choice of
pseudowire establishment mechanism is completely independent from the choice of
LSP establishment mechanism.
The procedures used to establish pseudowires using LDP are documented in RFC
4447. Because the pseudowire labels need to be known only to the PEs at either end of
the pseudowire, targeted LDP is used between them. Two new FEC types (TLVs) are
defined here.
PWid FEC The PWid FEC (also known as ???FEC 128???) was defined in the original
draft-martini and uses a dual-ended model, where the PE at either end of the pseudowire
are configured with an identical 32-bit PW ID that enables each to correlate
Figure 14.4 The Generic PW MPLS Control Word
Frg Sequence number Flags Length 0 0 0 0
MPLS 439
the label mapping sent to its peer with the label received from that peer. FEC 128 also
identifies the PW type (e.g., Ethernet VLAN, FR DLCI, etc.) and advertises a Group ID.
The Group ID provides a means of identifying a set of pseudowires??”for example, all
pseudowires corresponding to VLANs on the same physical port or all pseudowires being
carried over a specific LSP to the egress PE??”and may be used to notify the peer
of changes in status of all pseudowires in that set in a single operation.
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