IIRC, Cisco attempts a unicast refreash 60 seconds prior to expiration and again at-expiration if former fails.
I can't quiet remember but I think Rodney Dunn from Cisco had provided a very good explanation of the internals. Look for "ARP strangeness" or something like that in the archives from about a year ago. ./Randy --- On Mon, 1/21/13, Aaron <[email protected]> wrote: > From: Aaron <[email protected]> > Subject: Re: [c-nsp] unknown unicast flooding - particularly regarding fhrp's > To: "'Lee'" <[email protected]>, [email protected] > Date: Monday, January 21, 2013, 2:04 PM > 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: [email protected] > [mailto:[email protected]] > On Behalf Of Lee > Sent: Monday, January 21, 2013 12:23 PM > To: [email protected] > Subject: Re: [c-nsp] unknown unicast flooding - particularly > regarding > fhrp's > > On 1/21/13, Aaron <[email protected]> > 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 > _______________________________________________ > cisco-nsp mailing list [email protected] > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ > > _______________________________________________ > cisco-nsp mailing list [email protected] > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ > _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
