GLBP with 3 routers but only 2 of them to be active and the 3rd as hot stanby

Hi Team,

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I have been tasked with a project to implement a design to provide load balancing with 2 routers and once both of them are down then a 3rd one will take over the traffic.

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I have tried a few scenarios and designs but it seems that I am not be able to have 3 routers on the same GLBP group but only the 2 of them to operate as active forwarders.

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I think the key here is to play with the weighting but not sure what parameters to apply on the 3rd to take over the traffice when the other 2 are off.

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Thanks in advance