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A question about HSRP states

Mitrixsen
Level 1
Level 1

Hello, everyone.

I've connected one router to a network and configured HSRP on it. Since this was the only HSRP-enabled router, it became the Active router. However, I have a few questions about this debug output.

*Jan 16 11:53:32.351: HSRP: Gi0/1 Interface UP
*Jan 16 11:53:33.354: HSRP: Gi0/1 Grp 1 Init: a/HSRP enabled
*Jan 16 11:53:33.354: HSRP: Gi0/1 Grp 1 Init -> Listen
*Jan 16 11:53:44.815: HSRP: Gi0/1 Grp 1 Listen: c/Active timer expired (unknown)
*Jan 16 11:53:44.815: HSRP: Gi0/1 Grp 1 Listen -> Speak
*Jan 16 11:53:54.415: HSRP: Gi0/1 Grp 1 Speak: d/Standby timer expired (unknown)
*Jan 16 11:53:54.415: HSRP: Gi0/1 Grp 1 Standby router is local
*Jan 16 11:53:54.415: HSRP: Gi0/1 Grp 1 Speak -> Standby
*Jan 16 11:53:55.647: HSRP: Gi0/1 Grp 1 Standby: c/Active timer expired (unknown)
*Jan 16 11:53:55.647: HSRP: Gi0/1 Grp 1 Active router is local
*Jan 16 11:53:55.647: HSRP: Gi0/1 Grp 1 Standby router is unknown, was local
*Jan 16 11:53:55.647: HSRP: Gi0/1 Grp 1 Standby -> Active

During the Listen state, the local router listens for hellos but doesn't transmit any, correct? Then during Speak, it generates its own hellos and participates in the election. However, why did this router first become Standby and then Active the next second?

Also, what do the Active/Standby timers have to do with these states? Each time one of them expires, the state changes.

Thank you.

David

2 Accepted Solutions

Accepted Solutions

https://www.cisco.com/c/en/us/support/docs/ip/hot-standby-router-protocol-hsrp/10583-62.html <<- this link to check each status and if router send receive hsrp message and why status go to standby then to active 

MHM

View solution in original post

Richard Burts
Hall of Fame
Hall of Fame

David

You are correct in your observations. Yes at first the router just listens to determine if there is already an HSRP participant. When that timer expires the router sends its own HSRP hello to announce to any other router on the segment that it is participating in HSRP. Then the election takes place. It is in the design of the protocol that the first election is for standby, and from standby the router may become active. The router may not transition directly to active. This approach is quite similar to the OSPF election of BDR/DR where DR is not elected directly but is promoted from BDR.

The function of the timers is: When the router interface comes up it listens to determine if there are other HSRP participants on the segment. The active timer determines how long the router must listen before it advances to the next state. When the active timer expires the router advances to speak state where it sends it own HSRP packet. At this point there is no active router and no standby router. The standby timer determines how long the router spends in that state before it advances to the election. Since the router is the only participant at this point it becomes the standby router. And from standby the router is promoted to active.

HTH

Rick

View solution in original post

2 Replies 2

https://www.cisco.com/c/en/us/support/docs/ip/hot-standby-router-protocol-hsrp/10583-62.html <<- this link to check each status and if router send receive hsrp message and why status go to standby then to active 

MHM

Richard Burts
Hall of Fame
Hall of Fame

David

You are correct in your observations. Yes at first the router just listens to determine if there is already an HSRP participant. When that timer expires the router sends its own HSRP hello to announce to any other router on the segment that it is participating in HSRP. Then the election takes place. It is in the design of the protocol that the first election is for standby, and from standby the router may become active. The router may not transition directly to active. This approach is quite similar to the OSPF election of BDR/DR where DR is not elected directly but is promoted from BDR.

The function of the timers is: When the router interface comes up it listens to determine if there are other HSRP participants on the segment. The active timer determines how long the router must listen before it advances to the next state. When the active timer expires the router advances to speak state where it sends it own HSRP packet. At this point there is no active router and no standby router. The standby timer determines how long the router spends in that state before it advances to the election. Since the router is the only participant at this point it becomes the standby router. And from standby the router is promoted to active.

HTH

Rick
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