If the implicit null label is used, the protection tunnel label is popped and the tree SID P2MP LSPs are forwarded to the MP with the tree SID label.
In Figure: Protection using the implicit null label, node A is protecting link A-B through node C, so the facility protection tunnel is set up through node C. Node C is a PHP node and is programmed to swap the facility protection label with implicit null (label 3).
After a failure on the A-B link, node A pushes label 2000 as indicated in the protection next hop programmed in the replication segment for trees 1 and 2. Trees 1 and 2 share the same facility protection tunnel (label 2000). The packet is forwarded to node C, where node C pops the protection next hop and forwards the packet to node B with a replication SID on top of the packet.
