8.10 Route deletion hold function

The route deletion delay functionality delays the deletion from the routing table of routes that routing protocols have invalidated. Its use enables packet forwarding to be maintained over existing routes until an alternate route is available. The following figure shows an example of applying the route deletion delay functionality.

Figure 8-21: Example of applying the route deletion hold facility

In the figure above, a peer disconnect occurs between the priority router and the external-AS router A. This causes the Switch to disable its BGP4 routes until they can be re-learned from a non-priority router. However, the route deletion delay functionality stops the switch from deleting the routing information from the routing table, and packet forwarding is maintained through the following route:

Priority router -> Non-priority router -> External-AS router B

This function is applied when a numeric value in the range of 5 to 4294967295 (seconds) is specified as the route deletion pending timer value to be set by the configuration command routing options delete-delay.