MPLS and Traffic Protection

Typically, when an LSP fails, the router immediately upstream from the failure signals the outage to the ingress router. The ingress router calculates a new path to the egress router, establishes the new LSP, and then directs the traffic from the failed path to the new path. This rerouting process can be time-consuming and prone to failure. For example, the outage signals to the ingress router might get lost, or the new path might take too long to come up, resulting in significant packet drops. The JUNOS software provides several complementary mechanisms for protecting against LSP failures:

• Standby secondary paths—You can configure primary and secondary paths. You configure secondary paths with the standby statement. To activate traffic protection, you need to configure these standby paths only on the ingress router. If the primary path fails, the ingress router immediately reroutes traffic from the failed path to the standby path, thereby eliminating the need to calculate a new route and signal a new path. For information about configuring standby LSPs, see Configuring the Standby State.
• Fast reroute—You configure fast reroute on an LSP to minimize the effect of a failure in the LSP. Fast reroute enables a router upstream from the failure to route around the failure quickly to the router downstream of the failure. The upstream router then signals the outage to the ingress router, thereby maintaining connectivity before a new LSP is established. For a detailed overview of fast reroute, see Fast Reroute. For information about configuring fast reroute, see Configuring Fast Reroute.
• Link protection—You can configure link protection to help ensure that traffic traversing a specific interface from one router to another can continue to reach its destination in the event that this interface fails. When link protection is configured for an interface and configured for an LSP that traverses this interface, a bypass LSP is created that handles this traffic if the interface fails. The bypass LSP uses a different interface and path to reach the same destination. For information about configuring link protection, see Configuring Node Protection or Link Protection.

When standby secondary path, and fast reroute or link protection are configured on an LSP, full traffic protection is enabled. When a failure occurs in an LSP, the router upstream from the failure routes traffic around the failure and notifies the ingress router of the failure. This rerouting keeps the traffic flowing while waiting for the notification to be processed at the ingress router. After receiving the failure notification, the ingress router immediately reroutes the traffic from the patched primary path to the more optimal standby path.

Fast reroute and link protection provide a similar type of traffic protection. Both features provide a quick transfer service and employ a similar design. Fast reroute and link protection are both described in RFC 4090, Fast Reroute Extensions to RSVP-TE for LSP Tunnels. However, you need to configure only one or the other. Although you can configure both, there is little, if any, benefit in doing so.

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