GLBP Lab

Gotta remember...Cisco proprietary
Ran some debugs...saw that the hellos go to 224.0.0.102
*Mar  1 04:36:19.363: IP: s=172.16.10.100 (local), d=172.16.10.4 (FastEthernet0/0), len 100, sending
*Mar  1 04:36:20.075: IP: s=172.16.10.1 (FastEthernet0/0), d=224.0.0.102, len 88, rcvd 2
*Mar  1 04:36:20.995: IP: s=172.16.10.3 (local), d=224.0.0.102 (FastEthernet0/0), len 88, sending broad/multicast

Did a pretty standard config....3 routers connected to one switch.  Gave each fa0/0 interface a unique address on the 172.16.10.x/24 subnet, and applied the following config:
R1

(config-if)glbp 0 ip 172.16.10.100

(config-if)glbp 0 preempt

(config-if)glbp 0 priority 120

R2

(config-if)glbp 0 ip 172.16.10.100

(config-if)glbp 0 preempt

(config-if)glbp 0 priority 110

R3

(config-if)glbp 0 ip 172.16.10.100

(config-if)glbp 0 preempt

(received default priority of 100)

used show glbp [brief]
R3#sh glbp brief
Interface   Grp  Fwd Pri     State    Address         Active router   Standby router
Fa0/0            0    -      100  Listen  172.16.10.100  172.16.10.1  172.16.10.2
Fa0/0            0    1        -      Active   0007.b400.0001  local                    -
Fa0/0            0    2        -      Listen   0007.b400.0002  172.16.10.1         -
Fa0/0            0    3        -      Listen   0007.b400.0003  172.16.10.2        -

The - in the first line identifies the AVG, or active virtual gateway.  This is the device that distributes the created glbp mac-addresses to client within arp replies.  As you can see, there are 3 different AVF's represented by the 3 routers.  172.16.10.1 is the AVG, and 172.16.10.2 is standing by in case it fails.  You can also see which mac-address/ip address is associated with each AVF.  I also learned that the first AVF is actually going to be the first one to receive a client.