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sandu_nastas1
Beginner

VRRP: What happens if an interface fails ?

Hello,

I'm new to VRRP and I have a question that may sound stupid, but I couldn't find the answer in the Internet

If we consider the topolgy attached. We want to transfer info between R1 and R4 using R2 and R3. R1 has default-gateway: 192.168.1.3 and R4 : 10.0.0.3. We consider VRRP on R2 and R3, such as R3 is the master, and R2 - Backup (on both interfaces)

Ok. If R3 fails - R2 will take over. But, if only one interface from R3 fails (for example F0/0). Then - R1 starts transmitting to F0/0 of R2, which forwards the info to R4. But, when R4 replies - he will still send the data to R3's F1/0 interface, as he sees it as Master. R3 will have to drop the data, since it's F0/0 is down.

If we shut down both interfaces of R3 - then R2 completely takes over and the transmission goes well. How can this problem be solved ?

Thank you

4 REPLIES 4
Amit Aneja
Participant

This problem can be solved by tracking the interfaces & decrementing the priority of the HSRP interface if other interfaces are down.

If R3 is the master, then I assume it has higher priority, let's say 110.

R2 has 100, so it's backup.

If we configure tracking on R3 so that in case Fa0/0 goes does, it decrements the priority by 15 & makes it 95. This would call for a failover & R2 will become master.

Router3(config)# track 1 interface fa0/1 line-protocol

Router(config-track)# exit

Router3(config)# interface fa0/0

Router3(config-if)# ip address 192.168.1.x 255.0.0.0

Router3(config-if)# vrrp 1 ip 192.168.1.3

Router3(config-if)# vrrp 1 priority 110

Router3(config-if)# vrrp 1 track 1 decrement 15

Router3(config-if)# vrrp 1 preempt

Same goes for Fa0/1

Take a look at the foll doc:

http://www.cisco.com/en/US/docs/ios/ipapp/configuration/guide/ipapp_vrrp.html#wp1065881

HTH,

Amit

Hey, thanks a lot. Now I get it.

sandu_nastas1
Beginner

However - I still have one question: in this case - would it be correct to make the 2 interfaces of every router - members of the same VRRP Group ? or different groups ?.

For example: R2: F0/0 - VRRP 1 ; F1/0 - VRRP 2

                    R3: F0/0 - VRRP 1 ; F1/0 - VRRP 2

or

                    R2: F0/0 - VRRP 1 ; F1/0 - VRRP 1

                    R3: F0/0 - VRRP 1 ; F1/0 - VRRP 1

Thank you

Hi,

configuring tracking is only for interfaces not participating in the vrrp group.

Configuring multiple groups is often used for load sharing:

http://cciethebeginning.wordpress.com/2008/08/31/vrrp-and-load-sharing/

Regards.

Alain.

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