Computing forwarding tables for link failures

1. A method for maintaining a bridging network communication path table, the method comprising:

performing a shortest path first (SPF) computation to build a communication path table for a bridging network that has a transparent interconnection of lots of links (TRILL) topology with equal cost multipath (ECMP) paths, wherein the communication path table indicates a plurality of active ECMP paths between a first routing bridge and a second routing bridge in the bridging network, and wherein the SPF computation ranks each active ECMP path of the plurality of active ECMP paths based on: a link value that represents a number of links included in the active ECMP path, a reliability value for one or more of the links included in the active ECMP path, and an expected volume of traffic to be transferred through one or more of the links included in the active ECMP path;

determining a failed communication link between the first routing bridge and the second routing bridge in the bridging network;

identifying, in the communication path table, a first ECMP path of the plurality of active ECMP paths that includes the failed communication link; and

responsive to identifying the first ECMP path that includes the failed communication link, adding an indication to the communication path table that the first ECMP path is not active and postponing an SPF computation to rebuild the communication path table until a later time.

2. The method of claim 1 wherein the communication path table is stored at a third routing bridge, and the communication path table indicates paths originating at the third routing bridge.

3. The method of claim 1 wherein the communication path table is for one of: unicast traffic or multi-destination traffic.

4. A computer program product for maintaining a bridging network communication path table, the computer program product comprising program instructions stored on a computer-readable hardware storage device, the stored program instructions comprising:

program instructions to perform a shortest path first (SPF) computation to build a communication path table for a bridging network that has a transparent interconnection of lots of links (TRILL) topology with equal cost multipath (ECMP) paths, wherein the communication path table indicates a plurality of active ECMP paths between a first routing bridge and a second routing bridge in the bridging network, and wherein the SPF computation ranks each active ECMP path of the plurality of active ECMP paths based on: a link value that represents a number of links included in the active ECMP path, a reliability value for one or more of the links included in the active ECMP path, and an expected volume of traffic to be transferred through one or more of the links included in the active ECMP path;

program instructions to determine a failed communication link between the first routing bridge and the second routing bridge in the bridging network;

program instructions to identify, in the communication path table, a first ECMP path of the plurality of active ECMP paths that includes the failed communication link; and program instructions to, responsive to identifying the first ECMP path that includes the failed communication link, add an indication to the communication path table that the first ECMP path is not active and postpone an SPF computation to rebuild the communication path table until a later time.

5. The computer program product of claim 4 wherein the communication path table is stored at a third routing bridge, and the communication path table indicates paths originating at the third routing bridge.

6. The computer program product of claim 4 wherein the communication path table is for one of: unicast traffic or multi-destination traffic.

7. A computer system for maintaining a bridging network communication path table, the computer system comprising:

a processor(s) set; and

a computer-readable hardware storage device; and

program instructions stored on the computer-readable hardware storage device for execution by the processor(s) set, the stored program instructions comprising:

program instructions to perform a shortest path first (SPF) computation to build a communication path table for a bridging network that has a transparent interconnection of lots of links (TRILL) topology with equal cost multipath (ECMP) paths, wherein the communication path table indicates a plurality of active ECMP paths between a first routing bridge and a second routing bridge in the bridging network, and wherein the SPF computation ranks each active ECMP path of the plurality of active ECMP paths based on: a link value that represents a number of links included in the active ECMP path, a reliability value for one or more of the links included in the active ECMP path, and an expected volume of traffic to be transferred through one or more of the links included in the active ECMP path;

program instructions to determine a failed communication link between the first routing bridge and the second routing bridge in the bridging network;

program instructions to identify, in the communication path table, a first ECMP path of the plurality of active ECMP paths that includes the failed communication link; and program instructions to, responsive to identifying the first ECMP path that includes the failed communication link, add an indication to the communication path table that the first ECMP path is not active and postpone an SPF computation to rebuild the communication path table until a later time.

8. The computer system of claim 7 wherein the communication path table is stored at a third routing bridge, and the communication path table indicates paths originating at the third routing bridge.

9. The computer system of claim 7 wherein the communication path table is for one of: unicast traffic or multi-destination traffic.

10. The method of claim 1 , further comprising:

identifying a second ECMP path of the plurality of active paths in the communication path table; and

re-routing network traffic between the first routing bridge and the second routing bridge using the second ECMP path.

11. The method of claim 1 , further comprising:

responsive to determining that the failed communication link between the first routing bridge and the second routing bridge has been restored, indicating that the first ECMP path is active.

12. The method of claim 1 , wherein the SPF computation is postponed until a routine maintenance period occurs.