figure this one out

OK, i work in IT, i was called to the manufacturing floor this moring at 7am. Some PC's connected to a 3com HUB had no connectivity. I'll call this HUB1

I suspected that maybe HUB1 was being supplied by another HUB, or a switch that had went down, but there were no other people complaining of network issues and i coudn't trace the feed cable because it disapeared up into the suspended cable racks above the manufacturing floor.

So, i found another HUB (HUB2) further down the line, took a line from it and plugged it into HUB1, i stuck a laptop into a spare port and BINGO, i picked up an IP address and the PC's gained connectivity. So it looked like there was a problem with the initial cable going into HUB1 but i didn't know where it terminated so i called facilities to manually trace it for me.

Anyhoo, ten minutes later i got another call, every PC connected to HUB2 (the one i borrowed a line from) had lost connectivity, as well as HUB1 and the hosts attached to it.

Long story short, i eventually found the switch that was supplying HUB2 and the port on the switch that the HUB was plugged into was showing ERRDISABLE. After re-enabling the port, all hosts gained connectivity again.

Unfortunately we don't have a syslog server on the network, so when the switch error happened, no log was kept.

Do you think this was caused by too many collisions (running a hub from another hub)

Spanning tree violation?
Portfast?

I have no idea. What i do know is that we need to get our network sorted out. The only reason i figured this out was by methodically telnetting each switch in the factory and examining the port status on each. Luckily the switchport that supplied this HUB had been assigned with a friendly name that identified HUB2 (Bay 12 HUB) if you're interested

As it stands HUB1 is still running off HUB2, yet the port on the switch is still enabled.

Worrying..

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Comments

EdTheLad

My guess would be you have a loop.Hub1 might have an intermitent problem
and when it comes on line it screws with hub2.Your best bet is to draw a diagram of the network topology and troubleshoot from there!

Bearded Steve

ed_the_lad wrote:

My guess would be you have a loop.Hub1 might have an intermitent problem
and when it comes on line it screws with hub2.Your best bet is to draw a diagram of the network topology and troubleshoot from there!

Diagram, yeah. The trouble is the Facilities department. When asked to run in new network cables, instead of doing it the right way (cable from the patch panel in the comms room) they do it like this...

They have a stash of hubs and crappy 3com switches hidden in the racks above the shop floor. They just plug into one of them and don't bother marking the cable.

So our network is a mess of hubs and crap switches. I hate the fact that the cable management is handled by another department. Surely this falls under the remit of IT? Yet our boss does nothing about it. As long as the network chugs along he's happy.

Luckily the network is getting a complete overhaul soon. Time to take the power back. lol

Bearded Steve

Dammit.

Another port on another switch in a different comms room just disabled itself. No ERRDISABLE, just shutdown,

What the hell is happening today?

forbesl

Bearded Steve wrote:

So, i found another HUB (HUB2) further down the line, took a line from it and plugged it into HUB1, i stuck a laptop into a spare port and BINGO, i picked up an IP address and the PC's gained connectivity. So it looked like there was a problem with the initial cable going into HUB1 but i didn't know where it terminated so i called facilities to manually trace it for me.

Anyhoo, ten minutes later i got another call, every PC connected to HUB2 (the one i borrowed a line from) had lost connectivity, as well as HUB1 and the hosts attached to it.

Long story short, i eventually found the switch that was supplying HUB2 and the port on the switch that the HUB was plugged into was showing ERRDISABLE. After re-enabling the port, all hosts gained connectivity again.

It sounds like a port-security shutdown. Do you have port security enable on the switchports? If so, that is more than likely what caused the ERRDISABLE on that port after you connected another hub with more users hanging off it.

Bearded Steve

There's no security on that switchport. We ended up replacing HUB2 and it's working fine so there can't be security.

johnnynodough

what model of switch is it? whats it connected to, other switches? hubs wont send BPDU's, those ports that connect to hubs are just access ports, so that is rather odd, you can rule out STP, unless there is another switch connected to the hubs on another port. It would make more sense what fobesl said, that you have security problems, or perhaps to may errors being recieved on that port so it shutsdown. Of course configurable options are whats going to errdisable a port with the exception of STP, so sift through the config. hubs connected to hubs and bundles of wires can certainly propagate nasty errors.