Last Updated on August 1, 2021 by Admin 2
You are troubleshooting a problem with two routers configured in a HSRP group. You intended to configure the routers so that Router A and Router B would each track their respective Fa0/1 interfaces and decrement their priorities for several VLAN groups if the tracked interface went down. However, you find that Router A is not taking over as the active device for the HSRP group on VLAN 101 when the Fa0/1 interface on Router B fails.Which command would NOT be useful for discovering the problem?
- show running-configuration
- show vlans
- show standby brief
- show standby
The show vlans command would NOT be useful for discovering the problem. When troubleshooting a problem with Hot Standby Router Protocol (HSRP), the show vlans command will yield no useful information. The output of the command is shown below, demonstrating that there is no HSRP information provided.
All three of the remaining commands will be useful in discovering information. Each is shown below with an example of its application to troubleshooting.
Example A:show running-configuration
Router B is not taking over as the active device for VLAN 101’s HSRP group when the Fa0/1 interface on Router A fails. Below is a partial output of show run for both routers with the output focused on the section concerning VLAN 101’s configuration on each.
The above output displays the source of the problem. Router A has a decrement value of 5 configured for Fa0/1, as shown on the last line of the output after the specification of Fastethernet 0/1. This means that when its Fa0/1 interface goes down, Router A will subtract 5 from its priority for the VLAN 101 group, lowering it to 175. This is still higher than the priority of Router B, which is 170. Therefore, the solution is to change the decrement value for Router A to at least 11. When the interface goes down, Router A’s priority will be decremented to 169, allowing Router B to take the role as active for the HSRP group in VLAN 101.
Example B:show standby brief
Router C is not taking over as the active device for VLAN 102’s HSRP group when the Fa0/1 interface on Router D fails. Below is a partial output of show standby brief for both routers C and D, with the output focused on the section concerning VLAN 102’s configuration on each.
Interface Grp Prio P State Active addr Standby addr Group addr Fa0/1 102 200 Active local 10.10.10.253 10.10.10.251
Interface Grp Prio P State Active addr Standby addr Group addr Fa0/1 102 200 P Active local 10.10.10.253 10.10.10.251
The absence of a P in the P (preempt) column in the output for Router C shows that it is not set to preempt. If not configured to preempt, it will never take over for Router D, regardless of its priority with respect to Router D.
Example C: show standby
Router F is supposed to be the active router for VLAN 103’s HSRP group. Occasionally both routers are shut down for maintenance over the weekend. After the routers are rebooted, Router F is not taking over as the active device for VLAN 103’s HSRP group. Below is a partial output of the show standby command for both routers, with the output focused on the section concerning VLAN 103’s configuration on each
The output shows that Router F is not assuming the active role because of the priority and decrement values configured on the routers. When both routers go down, Router E will decrement its priority (200) by 10, as shown in last two lines of its output, leaving the priority at 190. Router F will decrement its priority (190) by 50 as shown in last two lines of its output, leaving the priority at 140. Therefore, to ensure that Router F maintains its role as active even after the dual shutdowns, the priority of Router F should be increased to at least 241. When both routers decrement their priorities after shutdown, Router F will then have a priority of 191, which will be higher than the priority value of Router E.
Configure and verify first-hop redundancy protocols