[c-nsp] unknown unicast flooding - particularly regarding fhrp's

[Aaron]

No arp entry, means router arps out to resolve l2 mac address of course

No answer to first ping is common and I recently read that it has something
to do with CEF throttling while it builds adjacency table entry

about the 5 minute arp timeout scenario....i believe that there is something
within cisco ios that when the arp timeout period elapses, (and I believe it
might be at half-life of timeout perios or something like that) that the
router itself actually proactively arp's out even before real traffic is
coming for that destination....in other words I think the router tries to
reach out to the pre-existing arp entries to see if they still exist at arp
timer halflife or something like that.  I think I saw that while doing
"debug arp" or something like that one day a while back

aaron



 

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Lee
Sent: Monday, January 21, 2013 12:23 PM
To: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] unknown unicast flooding - particularly regarding
fhrp's

On 1/21/13, Aaron <aaron1 at gvtc.com> wrote:
> Arp timers are central, bridge timers are more distributed
>
> Arp timers I believe are specific to svi/bvi/routed interfaces, bridge 
> timers I believe are more global and may not be vlan specific
>
> Those 2 items would lead me to think arp timers would be the best 
> place to adjust

What happens when the router doesn't have an arp entry?  When I ping an idle
host I don't get an answer to the first ping.  So if you set the arp timeout
to 5 minutes does that mean the 1st packet to a host that's been idle >= 5
minutes is dropped?

Thanks,
Lee
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