[c-nsp] Useful HSRP feature additions WAS: Rate limiting questions

Christopher E. Brown chris.brown at acsalaska.net
Fri Oct 26 16:10:20 EDT 2007

Phil Mayers wrote:
> On Fri, 2007-10-26 at 13:08 -0500, Justin Shore wrote:
>> Phil Mayers wrote:
>>>> Is there a HSRP option to tell the standby router to only route traffic 
>>>> when it's active?  VRRP and GLBP would have the same problem I imagine. 
>>> No. This is a frequently requested feature.
>> I think I'll ping my account team to add my voice to the list.  This 
>> seems like an awfully easy feature addition to me.  I can't think of any 
> At first hearing it does indeed seem easy. Having put some thought into
> why Cisco don't offer this (fairly obvious) feature, I've concluded
> there are some non-trivial difficulties doing it in the fully general
> cases that HSRP can support, and on some forwarding architectures.
>> downside to doing it either.
>> Justin

I think a more useful HSRP feature would be

standby 116 gratuitous arp 240

in order to solve the longstanding issues with MAC table aging v.s. ARP
table aging w/ HSRP.

I wouldn't think that generating grat arps for the HSRP address with the
HSRP MAC would be that hard.

Often you can change the arp timeout of the client machines/routers, or
the MAC table timeout, but not always.

When the routers are physically diverse and the subnet is say a SLB
group supporting FreeBSD machines...

Or worse yet, a redundant customer feed over metro ethernet where the
customer can't/won't reduce the arp timeout to < 5min.

Christopher E. Brown   <chris.brown at acsalaska.net>   desk (907) 550-8393
                                                     cell (907) 632-8492
IP Engineer - ACS

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