HSRP- maximum no of Routers in single Group

Unanswered Question
Giuseppe Larosa Thu, 11/06/2008 - 00:37

Hello Raju,

there is not an upper limit but:

all the routers that are not in Active or speak state will be in Listen state and will receive the HSRP hello messages from the Active and Standby that are sent to the multicast all routers on subnet.

A practical number can be three or four.

If you look for real load-balancing capabilities you may be interested in GLBP.

Hope to help


ciscosupport99 Thu, 11/06/2008 - 07:14

I have done a few GLBP instances after having done HSRP - GLBP is the BOMB! Check it out!

ciscosupport99 Thu, 11/06/2008 - 09:35

Hi Giuseppe,

Regarding GLBP - after using both HSRP & GLBP I wonder one one might choose HSRP over GLBP ?

Would you comment please ?


Giuseppe Larosa Thu, 11/06/2008 - 10:22

Hello JRobb,

GLBP is very good when there are many end users devices directly attached to the Vlan: this is because the AVG provides different answers to clients' ARP requests for the MAC of the default gateway.

There are cases where the two routers are offering a VIP to a single device that can be a Firewall or a Front-End of devices administered by another group/department and the two groups don't want to share dynamic routing information.

In a similar scenario GLBP is not able to provide its load-balancing capability because there is a single user and so once it makes an ARP request it will use only one router.

In these cases I would prefer HSRP to GLBP but actually a dynamic routing protocol would be better.

The reason ?

even in a high end routers like GSR every HSRP group takes an entry in the packet filter of the interface (a list of unicast and multicast MAC addresses that have to be processed) and this list was only made of 32 entries for every GE in a Engine 2 3GE linecard even using subinterfaces

The same happened in Cisco 7500.

Clearly HSRP is well known and GLBP being later starts to get popularity.

Hope to help


mhorsfield Thu, 01/12/2012 - 12:44

what is the maximum number of GLBP instances that can run on one box?  I want to run one instance of GLBP for each of my eight vlans, and possibly more vlans down the road.  is there a limitation to the number of GLBP instances running at one time on one box?  obviously GLBP is running on two redundant boxes...


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