HSRP questions

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Feb 10th, 2009
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Do the timers (hello and hold) have to match between HSRP routers? I thought they had to, but when I tried it in lab, it didn't make any changes to the existing active and standby roles.


What's the best practice of numbering "standby group number"? If I have two vlans between two HSRP routers, I tried using just "standby 1" for both interface vlans, and also "standby 1" for one vlan and "standby 2" for the other, but I didn't see any changes as far as the standby group functions.


Thanks a lot



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Laurent Aubert Tue, 02/10/2009 - 19:00
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Hi,


From the link below, you will read that the timers set on the active router override the timers configured on the other routers:


http://www.cisco.com/en/US/docs/ios/ipapp/command/reference/iap_s3.html#wp1062738


Standby group are used to create a unique virtual mac address (0000 0C07 ACXX where XX represents the HSRP group number) associated to the IP virtual address configured for this group. Layer 3 switches can handle the same mac address on different L3 interfaces that's why you can configure the same standby group on different VLAN interface.


HTH


Laurent.

ccannon88567 Wed, 02/11/2009 - 01:31
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I have just been reading up on this and Cisco recommend a best practice of naming the standby group number the same number as the vlan.


With many standby groups in an AS this makes sense but your standby group number can only be an integer of 0 - 255.


If your vlans are in numbers over 255 than this is not possible but with today's use of MLS local vlans it's normally a good practice.

gwhuang5398 Wed, 02/11/2009 - 11:18
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Thanks a lot. I always used "standby 1" for about half of the VLANs on the L3 switch, and "standby 2" for the other half of the VLANs. I never had any problems with it. But I never really though about why.


Thanks again

Giuseppe Larosa Wed, 02/11/2009 - 13:13
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Hello Gary,

actually on multilayer switches reusing standby groups is recommended there are some platforms that can use up to 16 different groups so it is good practice to use just a few of them.


Instead subinterfaces on routers for a different implementation requires to use a different standby group number on each.


Hope to help

Giuseppe


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