Specifications

CHAPTER 6
First Hop Redundancy
The actual router used by a host is its Active Virtual Forwarder (AVF). GLBP group members multicast hellos every 3
seconds to IP address 224.0.0.102, UDP port 3222. If one router goes down, another router answers for its MAC address.
Configure GLBP with the interface command glbp group-number ip virtual-IP-address, as shown:
Router(config-if)# glbp 39 ip 10.0.0.1
To ensure deterministic elections, each router can be configured with a priority. The default priority is 100:
Router(config-if)# glbp 39 priority 150
Hello and hold (or dead) timers can be configured for each interface with the command glbp group-number timers
[msec] hello-time [msec] hold-time. Values are in seconds unless the msec keyword is used.
GLBP can also track interfaces just as with HSRP. If a tracked interface goes down, another router answers for the first
router’s MAC address.
Planning Router Redundancy Implementation
Before configuring first-hop redundancy, determine which protocol is best in your network. If you have the same VLAN
on multiple access switches, use HSRP or VRRP. If you use local VLANs, contained to a single switch, GLBP is an
option.
Before configuring HSRP or VRRP on a multilayer switch, determine which switch is the root bridge for each VLAN.
The root bridge should be the active HSRP/VRRP router. Determine priorities to be used, and whether you need tracking
or timer adjustment.
After your implementation, verify and test. To view the switch’s standby status, use the show standby interface interface
command or show standby brief. To monitor standby activity, use the debug standby command.
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CCNP SWITCH 642-813 Quick Reference by Denise Donohue