Rerouting Around Failures; Ldp-Over-Rsvp Tunnel Protection; Abr Protection - Alcatel-Lucent 7450 Manual

Ethernet service switch

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Rerouting Around Failures

Every failure in the network can be protected against, except for the ingress and egress PEs. All

other constructs have protection available. These constructs are LDP-over-RSVP tunnel and ABR.

An RSVP LSP can deal with a failure in two ways.

If an ABR fails, then routing around the ABR requires that a new next-hop LDP-over-RSVP

tunnel be found to a backup ABR. If an ABR fails, then the T-LDP adjacency fails. Eventually, the

backup ABR becomes the new next hop (after SPF converges), and LDP learns of the new next-

hop and can reprogram the new path.

LDP-over-RSVP Tunnel Protection on page 546

ABR Protection on page 546

If the LSP is a loosely routed LSP, then RSVP will find a new IGP path around the failure,

and traffic will follow this new path. This may involve some churn in the network if the

LSP comes down and then gets re-routed. The tunnel damping feature was implemented

on the LSP so that all the dependent protocols and applications do not flap unnecessarily.

If the LSP is a CSPF-computed LSP with the fast reroute option enabled, then RSVP will

switch to the detour path very quickly. From that point, a new LSP will be attempted from

the head-end (global revertive). When the new LSP is in place, the traffic switches over to

the new LSP with make-before-break.

7450 ESS MPLS Guide