Chromebook won't get IP on WAPS connected to specific switch

[dgsmith]

Have recently encountered a very strange problem. One chromebook never seems to connect to wifi when in a certain part of the building (where the WAPs all route to the same switch), but move that device anywhere else in school (to a WAP on a different switch) and it connects straight away. As we have several 100 chromebooks in use now, no other device has this problem (even in the "problem" area). Really scratching my head over it. It's the "DHCP Lookup Failed" error but just this one device in wireless areas connecting to just 1 switch.

 

What could possibly be the issue when the device works fine everywhere else and every other device works fine everywhere?

[dgsmith]

Hi, I know this is quite obscure, but has anyone seen anything like it? Another chromebook now doing the exact same thing when connecting to wifi via this switch. Only seems to be IP address over wifi that isn't retrieved and connecting via wired is fine.

 

Really baffled as to what we can do to check this further or resolve. Would be crazy to take perfectly functional devices out of action just because they can't get an IP in one part of the school.

[Oaktech]

Have you restarted the switch and fully updated the firmware? I suspect the arp cache is not clearing on that switch. Most switches timeout the arp cache after 300 seconds, but if that mechanism isn't working you'll see that result.

[Davit2005]

You have not mentioned makes/models of WAPs or Switches but I'd check if there are any known issues on both on the current firmware. Wireshark can also be used to see if any of the process fails.

[dgsmith]

Hi, we use Aruba, mostly 2530. The switch had been rebooted (one through choice, one without choice..) and hadn't helped, though I do keep the firmware updated semi-frequently (maybe once or twice a year), though the switch itself is fairly new and was only updated around Sep.

 

However, I see there were 1 or 2 more recent firmware released so put the latest one on and it looks like the chromebooks get an IP now(!) I suspect the process of upgrading may have cleared something rather than "fixing" through the firmware itself being newer, though as the other firmware was fairly new, it wasn't an immediate thought.

 

I guess if in doubt, do it anyway!

[Oaktech]

Hi, we use Aruba, mostly 2530. The switch had been rebooted (one through choice, one without choice..) and hadn't helped, though I do keep the firmware updated semi-frequently (maybe once or twice a year), though the switch itself is fairly new and was only updated around Sep.

 

However, I see there were 1 or 2 more recent firmware released so put the latest one on and it looks like the chromebooks get an IP now(!) I suspect the process of upgrading may have cleared something rather than "fixing" through the firmware itself being newer, though as the other firmware was fairly new, it wasn't an immediate thought.

 

I guess if in doubt, do it anyway!

 

Glad it appears sorted. We had a similar problem with another flavour of HP switch and we discovered in conversation with HP that ARP and MAC table cache flushes were something that was suspended if the switch recieved a sustained high CPU usage. The high CPU usage on our switches also caused the switch to crash and the latest firmware solved the crashing issue, which was advertised in the changelog. The cache flushes continuing to occur in spite of the high CPU was just incidental, but important to us!

[Davit2005]

Hi, we use Aruba, mostly 2530. The switch had been rebooted (one through choice, one without choice..) and hadn't helped, though I do keep the firmware updated semi-frequently (maybe once or twice a year), though the switch itself is fairly new and was only updated around Sep.

 

However, I see there were 1 or 2 more recent firmware released so put the latest one on and it looks like the chromebooks get an IP now(!) I suspect the process of upgrading may have cleared something rather than "fixing" through the firmware itself being newer, though as the other firmware was fairly new, it wasn't an immediate thought.

 

I guess if in doubt, do it anyway!

 

Could well of been a switch reboot, I did see some issues before where a faulty switch caused the dhcp issue. It was a real cheap unmanaged switch though, cannot remember the name off my head.

 

We also had issue with some HP 2650's on a specific firmware and it was not reporting MAC addresses on uplinks or the local switch. Update of firmware sorted all of those though.

Edited January 12, 2022 by Davit2005

[dgsmith]

It's always a bit frustrating when you don't actually come to understand exactly what the issue is (or was) as you can't put anything in place or prepare for if it happens again. Switches are not the kind of thing you need to reboot often (or generally, at all) and I tend to only update firmware if I have some free time or if I know we have an issue fixed by a later release.

 

Still, thanks for the suggestions!