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Community Member

GLBP MACs

Given the fact that the AVG (in GLBP) responds to all ARP requests for the GLBP virtual IP address, how do the switches update their CAM tables quickly enough to ensure that the packet goes to the correct AVF?

For example:

GLBP IP address = 1.1.1.1

2 GLBP members #1 & #2.

#1 is the GLBP AVG

#1 MAC = 0000.0000.aaaa

#2 MAC = 0000.0000.bbbb

When a PC ARPs and #1 decides that the AVF #2 will forward the data for that PC it will source its ARP request with the MAC address 0000.0000.bbbb (#2).

The attached switch will update its CAM thinking that the MAC 0000.0000.bbbb is connected to #1.

Does #2 continually send out Gratuitous ARPs?

2 REPLIES
Silver

Re: GLBP MACs

GLBP load balances based on the MAC address so the devices are detecting only one MAC address coming from the firewall.

So only one GLBP router will be able to forward traffic and when ARP table refreshes the second router will forward traffic.

Community Member

Re: GLBP MACs

What I can't understand is that the AVG responds to all arp requests - thus the switch infrastructure (e.g. between the routers and the Firewall) will believe that all the MAC addresses (that the AVG responds to arp requests with) will be connected on the same interface.

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