What it does: When certain PathErr messages are received because a link went down, those links are marked as unavailable in the TE-DB for some amount of time. This holddown is to prevent headends from being told that the link is down via RSVP when the headends have not yet received an IGP update about the link's being down. If the links were not marked as unavailable in the TE-DB, when the headends try to find another LSP for the tunnel, because the IGP update has not arrived yet, the headends might choose a path over the very link that went down in the first place. This timer is the difference between the amount of time it takes for an RSVP message to get back to the headend and the amount of time the IGP takes to propagate the same information.
Default setting: 10 seconds
When to tune it: Increase this time if it takes your IGP longer than 10 seconds to converge; decrease it if your network has links that flap a lot and your IGP converges quickly when these links change state.
Recommendation: Make sure this number is no lower than the time it takes your IGP to converge. It's probably a good idea to set it to at least 2 * IGP convergence, to give things time to settle down. Your IGP should converge in a small number of seconds, but if you find that your IGP converges in more than 5 seconds, you should think about increasing this value slightly.
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