07-09-2009 12:28 PM
The switches they are connected to report what seems to me to be a high rate of errors consisting of type "Rcv-Err" and "Giants". The APs plugged into 2960, 3550 and 3560 POE switches report these errors at much lower rates, if any at all.
It wouldn't surprise me if the power injectors normally introduced some errors but the rate seems a bit excessive to me. Has anyone else notice this? Is this a common problem? If so what is an acceptable error rate for installations involving Power Injectors? Is there anything I can do to mitigate this problem?
07-09-2009 12:45 PM
These oversized MTU discovery packets are sometimes clocked as giant
errors. You can enable jumbo frames on the switches or you can
specifically set the AP MTU size in the AP system-profile on the
controller. When the MTU is specifically set, then MTU discovery does
07-09-2009 01:07 PM
In the AP system-profile, set the SAP MTU to 1500 bytes and the errors will disappear.
As Brian said, you could also increase the size of your MTU on your switches, but not all switches support jumbo frames. In your case:
2950 - no support
2960/3560 - Supported, but globally set for fe and ge ports. Must reload after executing the commands.
(config)# system mtu
(config)# system jumbo mtu
3550 - Depends on the model. The gigabit versions support up to 2000 bytes, the fastethernet versions up to 1546. So the 3550-12G and 12T can do 2000, the others are 1546, hence only the 12G and 12T could support Aruba's MTU discovery.
(config)# system mtu
07-10-2009 08:53 AM
The errors were indeed being caused by the MTU issue. The 2950s seemed to be counting the oversized packets as both Giants and Rcv-Error while the 2960s, 3560s, etc. counted them as just Giants.
The inflated count was from the APs not being able to contact their controllers for a few hours as the power injectors were put in before the switch ports were properly configured.
02-22-2010 03:15 PM
I notice a large burst of giants when the AP first boots and then a small trickle (5-10 an hour) following. Just more MTU traffic, I'm guessing?
Is this safe to ignore aside from the counter filling up? :eek: