Wednesday, August 26, 2009


Gotta remember...Cisco proprietary
Ran some debugs...saw that the hellos go to
*Mar  1 04:36:19.363: IP: s= (local), d= (FastEthernet0/0), len 100, sending
*Mar  1 04:36:20.075: IP: s= (FastEthernet0/0), d=, len 88, rcvd 2
*Mar  1 04:36:20.995: IP: s= (local), d= (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:
(config-if)glbp 0 ip
(config-if)glbp 0 preempt
(config-if)glbp 0 priority 120


(config-if)glbp 0 ip
(config-if)glbp 0 preempt
(config-if)glbp 0 priority 110

(config-if)glbp 0 ip
(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
Fa0/0            0    1        -      Active   0007.b400.0001  local                    -
Fa0/0            0    2        -      Listen   0007.b400.0002         -
Fa0/0            0    3        -      Listen   0007.b400.0003        -

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. is the AVG, and 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.

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