Label switched path preemption avoidance

1. A method comprising:

determining, by a router, whether a link is congested based at least in part on an amount of available bandwidth on the link; and

responsive to determining that the link is congested:

setting, by the router, a bandwidth subscription for the link, wherein the bandwidth subscription specifies a respective amount of bandwidth available for each different label switched path priority level from a plurality of different label switched path priority levels such that the amount of available bandwidth on the link for label switched paths having priority levels that satisfy a lower priority level threshold is less than an amount of available bandwidth on the link and less than the amount of available bandwidth on the link for label switched paths having priority levels that do not satisfy the lower priority level threshold; and

responsive to setting the bandwidth subscription, sending, by the router and to at least one other router in a network, an indication that a first amount of bandwidth is available for the label switched paths having priority levels that satisfy the lower priority level threshold and that a second amount of bandwidth is available for the label switched paths having priority levels that do not satisfy the lower priority level threshold, wherein the first amount of bandwidth is less than the second amount of bandwidth, and wherein the first amount of bandwidth is less than the amount of available bandwidth on the link.

2. The method of claim 1 , wherein setting the bandwidth subscription comprises:

initiating, by the router, an interior gateway protocol update; and

generating, by the router, an interior gateway protocol update message indicating that the amount of available bandwidth on the link for label switched paths having the priority levels that satisfy the lower priority level threshold is less than the amount of available bandwidth on the link for label switched paths having the priority levels that do not satisfy the lower priority level threshold,

wherein sending the indication to the at least one other router in the network comprises sending, by the router, the interior gateway protocol update message to the at least one other router in the network.

3. The method of claim 1 , wherein determining whether the link is congested further comprises:

receiving, by the router and from a management tool, a request for the amount of available bandwidth on the link, wherein the link is coupled to the router;

sending, by the router and to the management tool, the amount of available bandwidth on the link;

receiving, by the router and from the management tool, an indication of whether the link is congested; and

determining, by the router, whether the link is congested based on the indication of whether the link is congested.

4. The method of claim 1 , further comprising:

after determining that the link is congested and responsive to determining, by the router, that the link is no longer congested, determining whether the bandwidth subscription for the link is set; and

responsive to determining that the bandwidth subscription for the link is set, selectively removing the bandwidth subscription for the link.

5. The method of claim 4 , wherein selectively removing the bandwidth subscription from the link comprises:

determining, by the router, whether the amount of available bandwidth on the link satisfies a subscription removal threshold;

responsive to determining that the amount of available bandwidth on the link satisfies the subscription removal threshold, removing, by the router, the bandwidth subscription; and

responsive to determining that the amount of available bandwidth on the link does not satisfy the subscription removal threshold, maintaining the bandwidth subscription.

6. The method of claim 4 , wherein removing the bandwidth subscription for the link comprises updating, by the router, a traffic engineering database of the router to indicate that the amount of available bandwidth on the link for label switched paths having the priority levels that satisfies the lower priority level threshold is the same as the amount of available bandwidth on the link for label switched paths having the priority levels that does not satisfy the lower priority level threshold.

7. The method of claim 6 , wherein removing the bandwidth subscription for the link further comprises:

initiating, by the router, an interior gateway protocol update;

generating, by the router, an interior gateway protocol update message indicating that the amount of available bandwidth on the link for label switched paths having priority levels that satisfy the lower priority level threshold is the same as the amount of available bandwidth on the link for label switched paths having priority levels that do not satisfy the lower priority level threshold; and

sending, by the router, the interior gateway protocol update message to at least one other router in a network.

8. The method of claim 1 , wherein determining whether the link is congested comprises determining whether the amount of available bandwidth on the link satisfies an available bandwidth threshold.

9. The method of claim 8 , further comprising:

receiving, by the router, an interior gateway protocol update message from a different router in a network, wherein the interior gateway protocol update message specifies the amount of available bandwidth on the link;

updating, by the router, a traffic engineering database of the router with the amount of available bandwidth on the link; and

determining, by the router, the amount of available bandwidth on the link by at least querying the traffic engineering database for the amount of available bandwidth on the link.

10. The method of claim 1 , wherein setting the bandwidth subscription for the link comprises:

updating, by the router, a traffic engineering database of the router to indicate that the amount of available bandwidth on the link for label switched paths having the priority levels that satisfy the lower priority level threshold is less than the amount of available bandwidth on the link for label switched paths having the priority levels that do not satisfy the lower priority level threshold.

11. A router comprising:

a plurality of physical interfaces each having at least one link interconnecting the router as one of a plurality of routers in a network; and

a processor configured to determine whether a link of a physical interface of the plurality of physical interfaces is congested based at least in part on an amount of available bandwidth on the link, and, responsive to determining that the link is congested, set a bandwidth subscription for the link, wherein the bandwidth subscription specifies a respective amount of bandwidth available for each different label switched path priority level from a plurality of different label switched path priority levels such that the amount of available bandwidth on the link for label switched paths having priority levels that satisfy a lower priority level threshold is less than an amount of available bandwidth on the link and less than the amount of available bandwidth on the link for label switched paths having priority levels that do not satisfy the lower priority level threshold.

12. The router of claim 11 , wherein the processor is configured to set the bandwidth subscription by at least being configured to execute an interior gateway protocol update, generate an interior gateway protocol update message indicating that the amount of available bandwidth on the link for label switched paths having the priority levels that satisfy a lower priority level threshold is less than the amount of available bandwidth on the link for label switched paths having priority levels that do not satisfy the lower priority level threshold, and send the interior gateway protocol update message to at least one other router of the plurality of routers in the network.

13. The router of claim 11 , further comprising:

a computer-readable storage medium configured to store a traffic engineering database,

wherein the processor is configured to receive a request for the amount of available bandwidth on the link, wherein the link is coupled to the router, query the traffic engineering database for the amount of available bandwidth on the link, send the amount of available bandwidth on the link, receive an indication of whether the link is congested, and determine whether the link is congested based on the indication of whether the link is congested.

14. The router of claim 11 , wherein the processor is configured to, responsive to determining that the link is not congested, determine whether the bandwidth subscription for the link is set, and, responsive to determining that the bandwidth subscription for the link is set, selectively remove the bandwidth subscription for the link.

15. The router of claim 11 , wherein the processor is configured to selectively remove the bandwidth subscription by at least being configured to determine whether the amount of available bandwidth on the link satisfies a subscription removal threshold, responsive to determining that the amount of available bandwidth on the link satisfies the subscription removal threshold, remove the bandwidth subscription, and, responsive to determining that the amount of available bandwidth on the link does not satisfy the subscription removal threshold, maintain the bandwidth subscription.

16. The router of claim 11 , wherein the processor is configured to determine whether the link is congested by at least being configured to determine whether the amount of available bandwidth on the link satisfies an available bandwidth threshold.

17. The router of claim 16 , further comprising:

a computer-readable storage medium configured to store a traffic engineering database,

wherein the processor is configured to receive an interior gateway protocol update message from a different one of the plurality of routers in the network, wherein the interior gateway protocol update message specifies the amount of available bandwidth on the link, update the traffic engineering database with the amount of available bandwidth on the link, and determine the amount of available bandwidth on the link by at least querying the traffic engineering database for the amount of available bandwidth on the link.

18. A computer-readable storage device storing instructions that cause a processor to:

determine whether a link is congested based at least in part on an amount of available bandwidth on the link;

responsive to determining that the link is congested, set a bandwidth subscription for the link, wherein the bandwidth subscription specifies a respective amount of bandwidth available for each different label switched path priority level from a plurality of different label switched path priority levels such that the amount of available bandwidth on the link for label switched paths having priority levels that satisfy a lower priority level threshold is less than an amount of available bandwidth on the link and less than the amount of available bandwidth on the link for label switched paths having priority levels that do not satisfy the lower priority level threshold; and

send, to at least one other router in a network, an indication that a first amount of bandwidth is available for the label switched paths having priority levels that satisfy the lower priority level threshold and that a second amount of bandwidth is available for the label switched paths having priority levels that do not satisfy the lower priority level threshold, wherein the first amount of bandwidth is less than the second amount of bandwidth, and wherein the first amount of bandwidth is less than the amount of available bandwidth on the link.

19. The computer-readable storage device of claim 18 ,

wherein the instructions further cause the processor to set the bandwidth subscription by at least causing the processor to generate an interior gateway protocol update message indicating that the amount of available bandwidth on the link for label switched paths having the priority levels that satisfy a lower priority level threshold is less than the amount of available bandwidth on the link for label switched paths having priority levels that do not satisfy the lower priority level threshold, and

wherein the instructions further cause the processor to send the indication by at least causing the processor to send the interior gateway protocol update message to at least one other router in a network.

20. The computer-readable storage device of claim 18 , wherein the instructions further cause the processor to:

receive an interior gateway protocol update message from a different one of the plurality of routers in the network, wherein the interior gateway protocol update message specifies the amount of available bandwidth on the link;

update a traffic engineering database of the router with the amount of available bandwidth on the link;

determine the amount of available bandwidth on the link by at least querying the traffic engineering database for the amount of available bandwidth on the link; and

determine whether the link is congested by at least determining whether the amount of available bandwidth on the link satisfies an available bandwidth threshold.