MPLS Fundamentals

OAM Alert Label

In Chapter 3, “Forwarding Labeled Packets,” you saw a specific MPLS label called the Operation and Maintenance Alert label that has a value of 14. This label is specified by the ITU-T Recommendation Y.1711 and RFC 3429. You insert this OAM Alert label in the label stack just below the label(s) of the LSP under test. Cisco IOS does not use this special MPLS label anywhere. That is because the introduction of a special label in the label stack can influence the treatment of the packet when being forwarded. An example of this is the case of load balancing labeled packets, where the change in the label stack can introduce a different forwarding behavior. As such, the real user data traffic and the OAM traffic can be forwarded in ...