Alcatel-Lucent 7750 SR Manual page 802

PBB Features
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Identical procedure is used when the whole BEB C fails.
Page 802
In other topologies, it is possible that the BMAC C1 FIB entries in the B-VPLS instance
on the remote BEBs (like BEB A) will need to move between B-SAPs. This will involve a
move of all CMAC using as next hop BMAC C1 and the new egress IOM.
7750 SR OS Services Guide