Troubleshoot first hop redundancy protocols

Exam: Cisco 642-832 - Troubleshooting and Maintaining Cisco IP Networks (TSHOOT v1.0)

First hop redundancy protocols (FHRP) are meant to provide redundancy for the default gateway, which is the first hop for a packet leaving an end-point.

HSRP, VRRP & GLBP are all Fist Hop Routing Protocols. All of these protocols have different features but their foundation is based on the concept of Virtual IP that belongs to a router that acts as the active gateway for traffic. If this router fails, the VIP fails over to the secondary/standby router.

To troubleshoot Fist Hop Routing Protocols, the following steps can be helpful:

• The most common problem with FHRPs is that the routers are not able to see each other due to which they all become active. As a result, the end-point sees multiple active gateways resulting in abnormal network behaviour.
• Use the "show standy" command and note the status of the routers. In case of HSRP or VRRP, only one router should be in "Active" state while the other should be in standy sate.
• In most of the cases, the different rotuers are connected to 2 different switches which are trunked together. Ensure that the VLAN, to which the routers belong, is allowed in the inter-switch trunk.
• If the routers are connected to a single switch, ensure that the switch port on which the routers are connected are all in the same VLAN.
• For security purposes, each FHRP has an authentication feature. Make sure that the authentication is turned on on all the routers and the key matches on all the routers.
• On the end-point, make sure that the default gateway being used is the Virtual IP or the Standby IP.