R21xx-HP FlexFabric 11900 MPLS Configuration Guide

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Figure 60 Packet encapsulation
PW redundancy
PW redundancy provides redundant links between PEs so that the customer networks can communicate
when the path over one PW fails. As shown in Figure 61,
PE 1 establishes two PWs (one primary and one
backup). The CEs communicate through the primary PW. When the primary PW fails, PE 1 brings up the
backup PW and forwards packets from CE 1 to CE 2 through the backup PW. When CE 2 receives the
packets, it updates its MAC address table, so that packets from CE 2 to CE 1 also travel through the
backup PW. Only static PWs and LDP PWs support PW redundancy.
Figure 61 PW redundancy
The MPLS L2VPN determines whether the primary PW fails according to the LDP session status or the BFD
result. The backup PW is used when one of the following conditions exist:
• The primary PW goes down because the public tunnel of the primary PW is deleted, or BFD detects
that the public tunnel has failed.
• The primary PW is deleted because the LDP session between PEs goes down, or BFD detects that the
primary PW has failed.
• A manual PW switchover is performed.