A packet received with a label matching either a node SID or an adjacency SID is forwarded according to the ILM type and operation, as described in the following table.
Label type |
Operation |
|---|---|
Top label is a local node SID |
The label is popped and the packet is further processed. If the SID label of the popped node is at the bottom of the stack label, the IP packet is looked up and forwarded in the appropriate FIB. |
Top or next label is a remote node SID |
The label is swapped to the calculated label value for the next-hop and forwarded according to the primary or backup NHLFE. With ECMP, a number of primary next-hops (NHLFEs) are programmed for the same destination prefix and for each IGP instance. ECMP and LFA next-hops are mutually exclusive. |
Top or next label is an adjacency SID |
The label is popped and the packet is forwarded out of the interface to the next-hop associated with this adjacency SID label. In effect, the data path operation is modeled like a swap to an implicit-null label instead of a pop. |
Next label is BGP 3107 label |
The packet is further processed according to the ILM operation. The BGP label may be popped and the packet looked up in the appropriate FIB. |
Next label is a service label |
The packet is looked up and forwarded in the Layer 2 or VPRN FIB. |
A router forwarding an IP or service packet over an SR tunnel pushes a maximum of three transport labels with a remote LFA next-hop.