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New Member

WS-2950's Dropping VLAN1 connectivity

Hi there,

First off yes yes its EOL. Big companies like to use network infrastructure till it catches on fire and only then they will blame you and replace it with a network refresh you have quoted them on a 100 times in the past.

Anyhow. I have a problem where only the 2950's switches go transperant. They drop VLAN1 thus no CDP snmp packets. The users keep working fine but our NMS center keeps calling me at 3am when this happens.

These are access switches that connect to stacked 3750's. Some of the uplinks are using media converters that i have been trying to get removed. But i doubt that it could be the cause of the vlan1 going down.

Any Ideas would help. I can how ever due to copy right aggreements not give any configs here regarding this client :<

Just some Ideas will help cause I am out of them

New Member

WS-2950's Dropping VLAN1 connectivity


did this setup ever work properly? if yes, was something changed in the past?

by saying "dropping vlan1 connectivity" you mean that all devices connected to vlan1 loose the connection to each other?

does this always happens at the same time?

the users are in a different vlan?

what if you are connected to vlan1 on lets say switch A and try to communicate with a device in vlan1 which resides on switch A as well while this problems occurs?

i know these are some standard questions, but try to understand the scenario a bit better.


New Member

WS-2950's Dropping VLAN1 connectivity

Hi thanks for the reply.

Your first two questions I can not give feed back on. Most cases you Adopt a network and find it in a dismal state.

The  timing is random. There are 6 vlans only the management vlan drops  connectivity and its set on vlan 1. As you know vlan 1 transports your  CDP protocols as well. So even doing a CDP neighbor command doesnt show  the switch. But if you are on the "data" vlan you can communicate to the  "printer" vlan with no problem. But not to vlan1. Also the funny thing  is when this happens all the lights on the switch stays static excluding  the trunk ports that flashes between amber and green.



New Member

WS-2950's Dropping VLAN1 connectivity

hi daniel,

what do you have to do to get the vlan1 back?

how many 2950´s do you have?

is there a lot of traffic in your network, like backup jobs or server sync?

what kind of traffic is on vlan1, besides the CDP?

what IOS version is running on the 2950´s and have you checked if there maybe is a bug known to that IOS verison?

it is indeed a strange behaviour and i have never heard of it before.

its also weird that the lights of the switch stay static, could be related to a high cpu utilisation.

here is a document which could help you to figure out if its the cpu.


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