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Routing behaviour with VRRP Fabric Routing

  • 24 September 2020
  • 1 reply
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VRRP fabric routing allows a VRRP backup router to take part in L3 routing and forward packets that would have to be routed by the VRRP master if fabric routing was not enabled.

What is not clear from the documentation is where the backup router will potentially route packets to.

Say R1 is a VRRP master and R2 is a VRRP backup router with fabric routing enabled. Both R1 and R2 have different default routes in their routing table learned from elsewhere in the network.

A packet arrives that will be routed via the default route - as R2 is closer to the switch which this packet arrives from it deals with the routing for this packet.

Which of the following does R2 do:

1 - Simply route the packet according to its own routing table, resulting in traffic potentially taking a different route than if it had been handled via the VRRP master (R1).

2 - Route the packet as if it were the VRRP master - this would involve R1 having somehow informed R2 of what route to use.

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Best answer by Miguel-Angel RODRIGUEZ-GARCIA 24 September 2020, 23:19

Hi Jon,

R2 can only use his own routing table, so answer 1.

Concerning your point “Both R1 and R2 have different default routes in their routing table learned from elsewhere in the network”.

It would be a very very very bad idea to design your VRRP cluster with fabric routing and the members being able to learn something that the other can’t/wouldn’t.

It is possible to go for setups where the members can learn different things and there are use cases for that but in this case disable the fabric routing and set priorities on the VRRP master/backup members to allow only one active router at a time.

Cheers

 

Mig

 

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Hi Jon,

R2 can only use his own routing table, so answer 1.

Concerning your point “Both R1 and R2 have different default routes in their routing table learned from elsewhere in the network”.

It would be a very very very bad idea to design your VRRP cluster with fabric routing and the members being able to learn something that the other can’t/wouldn’t.

It is possible to go for setups where the members can learn different things and there are use cases for that but in this case disable the fabric routing and set priorities on the VRRP master/backup members to allow only one active router at a time.

Cheers

 

Mig

 

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