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2950 switches and UPS


I?m having a strange problem with a rack of 2950 switches when they come back up after a power outage.

The college I work at is subject to semi-frequent blackouts in the dorms due to electric infrastructure issues in a rural area.. We have a UPS on each switch rack so that students, almost all of whom have laptops, have a few minutes to close and save networked files before the network access goes down.

The problem is that most, but not all, of the 2950 switches do not switch frames routed back from the core on the VLAN when the UPS runs out of juice and shuts down. This was first observed as DCHP requests going to the server but clients never receiving the offer. Further testing revealed that statically configured clients do not work either. However, there is no problem with ping-telnet on the management VLAN of the switch itself.

This does not happen when the UPS is just unplugged but it does happen if it is put in sleep mode, turned off, or runs out of juice.

The only consistent thing we can find is that it never happens on 2900 switches but not all 2950 switches. By all appearances the switches should be working right. There is no STP block on any ports, green lights are on, VTP functions and the right VLAN information is there, and all ports with PC?s running on them read as up and running normally in the configuration.

So far the only fix seems to be to manually cycle the power on each effected switch. Obviously this is a real problem with power goes out overnight on a weekend.

Does anybody have any experience with this or have any suggestions on how to deal with it?

We can?t really afford to buy new UPS?s right now. And even if we did there seems no guarantee that it would solve the problem


Re: 2950 switches and UPS

Sounds strange, troubleshoot the issue just as you would any connectivity issue. First, eliminate the DHCP by static ip address to testing connectivity, make ip addresses assigned are correct including mask, default gateway, etc. 2. Ping from device in the same switch to another device connected in the same switch in the same vlan to see if L2 is fine. 3. Then ping that PC default gateway, then the routers other interfaces if there are more than one to see if the router is switching packets. If you have a ping failing on any of the steps, there is not need to proceed to the next step, Hopefully this would help you track down the issue, UPS should not affect packet switching of the device.