GLBP Timers

iamme4eva

Hey,

Just wondered if someone could help clear something up?

I think I've got my head around the GLBP timers - for the duration of the redirect timer the AVG will keep giving out the MAC of the failed AVF, in the hope that it will come back online.

For the duration of the timeout timer, the AVF that took over the failed AVF's duties will carry on answering frames on behalf of it. After the timeout timer, all of the peers will flush the MAC address of the failed AVF and that's the end.

If I do actually have that right, my question is this:

If, for the duration of the timeout timer, another AVF is using the failed AVF's MAC address, then surely the ARP entry will never age out of any devices ARP cache, as frames with the failed MAC are still being seen? This would mean that once the timeout timer expired, all devices that were using failed MAC will then lose connectivity until their ARP entry expires?

Thanks.

Nick.

iamme4eva

Never mind. I labbed it. I was right, after the four hours then connectivity would be lost if the address was still cached. However, it seems that Windows, and I guess other systems, forces a refresh of everything in the arp cache periodically. I changed the timeout timer to ten minutes and kept a constant ping going, and about 8 minutes in the mac address in the cache changed for seemingly no reason, and with no outage.

For information, it seems that arp entries age out between 30-45 secs of inactivity in Windows, plus a force refresh around every ten minutes. I couldn't find any documentation to support it, but that's my findings.