HSRP flapping

[sonny.wigmore]

                   Hello all,

Wondering if anyone can explain/help me understand the following situation:

The primary had a flap on HSRP and since recovered, however the secondary continued to flap between active > speak, speak > standby.

The primary stayed in Active, and the secondary also said it was changing to Active. Though the primary was carrying the traffic.

Can you please help me understand?

FastEthernet0/0 - Group 10

  State is Standby

    1 state change, last state change 1d05h

  Virtual IP address is 10.146.193.129

  Active virtual MAC address is x

    Local virtual MAC address is x(v1 default)

  Hello time 3 sec, hold time 10 sec

    Next hello sent in 2.652 secs

  Authentication text "xxx"

  Preemption enabled

  Active router is 10.146.193.130, priority 150 (expires in 8.060 sec)

  Standby router is local

  Priority 110 (configured 110)

  IP redundancy name is "hsrp-Fa0/0-10" (default)

What I did notice previously was that the active router was Unknown. I have tried to use cdp neighbor to work out what sits between the 2 routers, cdp only picks up the neighbouring router.

Any advice would be much appreciated.

[Raju Sekharan]

Hi Sonny,

If there is packet loss between HSRP Primary and Active, you will notice the standby flapping between Active and standby because

1. if it doesn' receive the hellos within hold-dwon timer of 10 seconds , it thinks active is down and will take the active role

2. If again it receives a hello, it will go back to standby

The primary doesn't change the state, because it is already active. if there is packet loss to standby, you can notice it only in the show standby output

Your problem indicates a packet loss between these 2 routers. it can be due to link issues, high cpu, ....

[sonny.wigmore]

Ok thanks for your reply.

I understand your explanation thanks however would this not be reflected on the primary also? As we were only seeing the state changes on the Secondary, the Primary remained active?

I did ping across the LAN however there wasnt any packet loss when I tested it, I presume it cleared up hence when I came to ping it the state changes had stopped.

Your response would be appreciated

[Raju Sekharan]

Hi Sonny,

Show log will report if there is an HSRP state change

When there is intermittent packet loss between active and standby.the state change is happening only on standby. That is why it is getting reported only standby

During the issue, if you look at " show standby" output you will be able to see " standby unknown"

I have seen this behavior for many customers

Thanks

Raju

*** rate if the post helps ***

[sonny.wigmore]

Ok thanks, as long as this is normal behaviour as a result of packet loss that is OK. It has cleared up now however I wanted to make sure I understood incase it happened again.

Thanks

[Raju Sekharan]

Yes. This is normal behavior.

Thanks

Raju