Route preference using an Offset List
Here's the scenario, R1 has 2 potential routes to R6 and you want 1 route preferred and the other to stay in the topology table as a backup. This example uses equal cost, but this will also work with unequal cost routes as long as they have the same Administrative Distance and both routes exist in the topology table.
To influence R1 to use the path through R2, you will apply an offset list "out" on R3 R3(config)# access-list 1 permit 2.2.2.0 R3(config)#router eigrp 100 R3(config-router)#offset-list 1 out 34567 <-- Uses access-list 1 with an offset of 34567 R3(config-router)#end On R1 the route via R3 will become less desirable, but still be available in the topology table in case the route via R2 disappears. Before (lines omitted for brevity): D EX 2.2.2.0 [170/28416] via 10.4.0.9, 00:12:46, FastEthernet1/0 [170/28416] via 10.4.0.5, 00:12:46, FastEthernet0/0 And 10.4.0.5 (FastEthernet0/0), from 10.4.0.5, Send flag is 0x0 Composite metric is (28416/2816), route is External 10.4.0.9 (FastEthernet1/0), from 10.4.0.9, Send flag is 0x0 Composite metric is (28416/2816), route is External After (lines omitted for brevity): D EX 2.2.2.0 [170/28416] via 10.4.0.5, 00:12:15, FastEthernet0/0 And 10.4.0.5 (FastEthernet0/0), from 10.4.0.5, Send flag is 0x0 Composite metric is (28416/2816), route is External 10.4.0.9 (FastEthernet1/0), from 10.4.0.9, Send flag is 0x0 Composite metric is (62976/37376), route is External You'll see the metric for the second route is much higher now but it is still available should the 1st route go away. ***Note: This technique could also have been applied inbound, on R1 toward R3 using the command: R1(config-router)#offset-list 1 in 34567 FastEthernet 1/0 |