[c-nsp] HSRP Groups on ASR1k

[Phil Mayers]

On 09/28/2010 06:31 PM, Benjamin Lovell wrote:
>>
>> Is this right?
>>
>> Isn't the HSRP MAC the same for a given group number, regardless of
>> which sub-int?
>>
>> We run all our interfaces (not ASR1k though) in "standby group 0"

> BL> It varies by platform. The 3K series switches for example also use
> the VLAN ID and will give you 256(i think) unique MACs even if using the
> same group ID. Either way using the same or no group ID is defiantly not
> Cisco's recommendation.

That's interesting. We don't see that on the (few) 3750s we've got 
routing - the one routing our subnet is 00:00:0c:07:ac:00 but the SVI is 
(obviously) vlan tag.

Why do Cisco recommend against using the same group ID? What's the problem?

>>
>>>
>>> This could be a software limitation that was addressed or is planed
>>> to be addressed in later code releases or it could be a hard limit of
>>> the NIC used on the SPAs. I would open a case with the TAC to have
>>> them talk to the devs about this and see if it will be important to
>>> you.
>>>
>>> BTW - not clear on the part where you said you are using HSRP groups
>>> 1 and 2 on the customer sub-ints. You should use a unique standby
>>> group for each HSRP instance. If you are not this *may have something
>>> to do with your problem.
>>
>> Why? Using a different standby group per sub-int will surely
>> definitely run you over the mac receive filter size limit? What's the
>> problem using the same group number on different interfaces?
>
> BL>It's certainly possible/likely but this is really a matter of
> platform knowledge about how the ASR 1K does MAC filtering / HSRP MAC
> assignment. I am not that deep into the ASR 1K platform and unless one
> is it would not be wise to jump to conclusions.

Fair point.

However, on the 6500 under 12.2(33)SXI, the standby group is limited 
from 0-255. This means it could only do HSRP on 255 subnets; we do way 
more than that, and I'm sure customers elsewhere do. If there's a 
problem lying under the hood re-using the group ID, it would be good to 
know what it was.

>
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