HSRP Active-Active configuration

[Sihanu N]

Hi Experts,

We have a current scenario with two core switches (4503) having HSRP one in Active and other in Standby mode. Since the active core switch utilization increased in now a days, we are planning to configure HSRP as Active-Active Configuration. But now all the 30 vlans are using the same standby group (standby group 1).

My queries are

1) Should we go ahead with active-active hsrp configuration by keeping the standby group 1 for all vlans or use unique group for each vlans

2) Should we give the command standby preempt command in both switches

3) Any downtime needed for the configuration change

Please provide your valuable suggestion to my queries

Advance Thanks and Regards

Sihanu N

[Reza Sharifi]

Hi,

How do you know that HSRP causing high utilization?  You only have 30 vlans and a 4500 in active stand-by mode should be able to handle that very easily.  I suggest looking at other sources for high utilization problem. If you think with only one group your utilization is high, you certainly will have even higher CPU utilization if you configure one per vlan (30 HSRP groups)

HTH

[Richard Burts]

Reza

With all due respect I wonder what you think will cause CPU utilization to be higher if there are 30 unique groups doing HSRP or 30 VLANs doing HSRP and all using the same group. It seems to me that the HSRP processing for each VLAN will be the same whether they all use the same group number or each uses a separate number.

For management and troubleshooting I can see advantages in having unique group numbers. But I do not see any implications for CPU utilization in that decision.

Sihanu N

Perhaps I am not clear what you mean when you ask about active-active configuration of HSRP. Perhaps you could clarify?

I can perhaps understand that if switch 1 is the active interface for all 30 VLANs and switch 2 is the standby interface for the 30 VLANs that there might be some performance imbalance between the switches. In this situation I have seen some people who implement HSRP so that switch 1 is active for all odd number VLAN and switch 2 is active for all even numbered VLANs. And I have seen some people who configure two HSRP groups for each VLAN and have switch 1 active for the first group and have switch 2 active for the second group. This requires that clients with each VLAN have some clients configured to use the standby address for the first group and other clients within the VLAN configured to use the standby address for the second group. Either of these approaches could address the performance imbalance.

So perhaps you can clarify what you are trying to achieve?

HTH

Rick

[Reza Sharifi]

Hi Rick,

The reason I noted that the more groups the higher CPU is because each HSRP group has to maintain a separate state and timer for each group.  So maintaining multiple HSRP groups to me can only consume more memory and CPU, especial during times when network is not very stable and the router has to go through so many state changes.

It would be more helpful if OP could provide some more details starting with "sh cpu process"

Regards,

Reza

[Richard Burts]

Reza

From my perspective it is a question of 30 instances of HSRP each using group 1 or 30 instances of HSRP with each instance using a different group number. In either case it looks to me like the same amount of CPU utilization to maintain state and timer information for each instance. Do you see a difference from your perspective?

HTH

Rick

[Sihanu N]

Thanks for your valuable suggestions and reply

I mean the HSRP Active-Active configuration like making the HSRP as both redundant and load balancing. Now it is configured as just like Active-Standby mode (Core1 - Active for all vlans, Core 2- Standby for all vlans). I need to make the configurations such as to make Core 2 to more utilized by increasing the standby priority for some vlans, so that the load for Core 1 will reduce and at the same time keeping the switches as redundant to each other.

Regarding the CPU utilization i will post the sh process cpu and related outputs, now i am not in the office.

Please provide the answers to my queries

1)  Should we go ahead with active-active hsrp configuration by keeping the  standby group 1 for all vlans or use unique group for each vlans

2) Should we give the command standby preempt command in both switches

3) Any downtime during the configuration change

Thanks

Sihanu N

[viswamin · Accepted solution]

Hi sihanu.

As Richard Suggested, if you want to acheive load balancing, then create two group of vlans each containing 15 Vlans make your configuration something like this.

Let SW A be the HSRP Active for Vlan Group  I and SW B be the Standby for the same Vlan Group I

Let SWB he the HSRP ACtive for Vlan Group  II and SW A be the standby for the same Vlan Group II

that way you should be able to load balance.

To answer you questions:

Sihanu N wrote:
1)  Should we go ahead with active-active hsrp configuration by keeping the  standby group 1 for all vlans or use unique group for each vlans
2) Should we give the command standby preempt command in both switches
3) Any downtime during the configuration change
Thanks 
Sihanu N

1. Performing configurations as stated above will provide redundancy as well as load balancing.

2. Yes ..

3. There will be downtime but may be a couple of seconds and not more .

HTH

-Vijay

[Latchum Naidu]

Hi Sihanu,

This is what called per VLAN hsrp, it means the both routers will be in active active with two different groups.

See the below link for more informaiton.
http://www.firstdigest.com/2009/04/cisco-how-to-configure-hsrp-for-load-balancing-traffic/

Please rate all the helpfull posts.
Regards,
Naidu.

[Sihanu N]

Thanks for your valuable response to my queries Vijay Swaminathan. Now i got the idea of HSRP load balancing between the switches.

Now the current hsrp configuration uses single standby group for all vlans (standby group 1). One last query regarding this(just for information)

1) Is there any problem occurs by keeping the single standby group 1 for all vlans for the load balancing the HSRP between the core switches. I just want to know significance of using different standby group no. , just know the information.

Kindly provide your valuable suggestions.

Advanced Thanks and Regards

Sihanu N