Generic Failure Types

This section discusses generic failure types within the context of MPLS-based networks. These include interface failures, pseudowires, and LSP failure conditions.

Interface Failure

Interface failure events are defined as loss of signal, loss of frame, SONET AIS, and so on. These are also known as line failures and usually occur in the CE-PE link. If a line failure occurs on the core side, it usually triggers a change in Internet Gateway Protocol (IGP) adjacency, resulting in LSP tunnel failure.

Pseudowire Failures

PW failures are triggered under the following conditions:

• When the targeted LDP keepalive session between the edge PE fails or times out.

• When a link flap or failure occurs on the core network side resulting in loss of adjacency in IGP. This triggers a tunnel failure cascading into a failure of the individual pseudowires that are carried in the tunnel.

• MPLS OAM-related failures. MPLS OAM techniques, such as VCCV, MPLS, and LSP ping are able to detect the health of the PW.

Tunnel LSP Failures

Any failures on the control plane due to timeouts or link failures in network affect the IGP adjacencies and are reflected as tunnel LSP failures. Depending on whether MPLS fast reroute is configured, the tunnel LSP can be rerouted or an alternate path can be found.

For MPLS to be a viable convergence technology, a number of things need to be achieved when considering replacing it with traditional transport technologies or using it as glue to stitch together different layers and create new services. These are as follows:

• Preservation of necessary operational semantics (for example, consistency at the client layers)

• Common behavior of interworking functions (how it acts does not depend on any peer IWF)

• Minimal messaging to convey all requisite information

• Consistent behavior even under multiple fault scenarios (faults notified promptly and cleared properly)

• No unrecoverable states requiring manual intervention

• Consistent behavior no matter what the chain of interworking is (not limited to attachment circuit <->PW<->attachment circuit)

• Works for all interworking scenarios and mixes of technologies

Therefore, you need to consider these emerging interworking OAM and OAM message mapping mechanisms and applicability when deploying Any Tranport over MPLS-based services.