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

[Roger Oliver]

In the load balancer I use (F5 BigIP) they allow you to asign a mac address to you floating ip (which in this case woukd be hsrp) this mac is set up on both units but only becomes active a gru--aprs the mac when the other ipaddress  dies this failover happens very fast. In this way only the active interface routes. While I know being able to modify any mac can be bad ithought it might stilll be something that would be intereing to see 


Roger 
AIM: ippaku



-----Original Message-----
From: "Phil Mayers" <p.mayers at imperial.ac.uk>
To: "Christopher E. Brown" <chris.brown at acsalaska.net>
Cc: "Cisco-nsp" <cisco-nsp at puck.nether.net>
Sent: 10/27/07 7:06 AM
Subject: Re: [c-nsp] Useful HSRP feature additions WAS: Rate limitingquestions

On Fri, 2007-10-26 at 12:10 -0800, Christopher E. Brown wrote:
> 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.

As I understand it, the "longstanding" arp/mac aging mismatch issue
occurs when traffic is returning via the standby and the standby ages
out the mac entry because it isn't seeing the outbound packets.

The hsrp master doing grat. arps for itself doesn't address that, does
it?

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

It wouldn't. I don't see how it would solve the problem though.

> 
> 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.

Reducing the arp timeout to <5 min is a bad idea anyway, for a number
of reasons.

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