3ad link aggregation, using LACP signalling). In this case, the two remote PEs will
agree which is active and which is standby and will signal appropriate status to the local
PE. Should the active remote PE, or the link from that PE to the protected CE, fail,
then the standby remote PE will assume the active role. Note that switchover in the
case of PE-CE link failure is triggered by the Layer 2 redundancy protocol.
Ethernet Pseudowires There are two different types of Ethernet pseudowire, both defined
in RFC 4448:
?– Tagged mode In this mode, each transported Ethernet frame must contain at
least one 802.1Q VLAN tag, and both PEs must agree how to process the tag. This
mode exists because many routers available at the time the original draft-martini
was written were unable to add and remove VLAN tags. If the VLAN tag is different
on the ingress and egress PE, then the tag is rewritten at egress??”though it
may be rewritten at ingress if the egress PE has signaled the optional requested
VLAN ID and if the ingress PE is able to rewrite the tag at ingress.
Figure 14.5 Redundant Pseudowires
CE running
802.3ad to
Dual PEs Standby PE
Active PE
Active pseudowire
Standby pseudowire
MPLS network
PE
CE
442 Chapter 14
?– Raw mode In this mode, the transported Ethernet frame may contain 802.
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