Question : Why are batches of users losing LAN access?

Hi
Hope someone can help with this one. We're a single site office with a number of rooms cabled into the comms room. Rooms pretty much use a switch each.

Had very few problems until last week.

- Last week a batch of users lost access to the LAN, that batch was around 8 users in one room. The remaining 15 users in that room were unaffected. While investigating the problem I temporarily connected them via a known good connection using an 8 port netgear switch to restore access.

Symptoms: connected to the network, but unable to renew IP address. Only 'limited' connectivity was reported by XP pro. It wasn't PC specific because known good laptops had the same problem when plugged into this connection.

We checked the cabling using a tester - this was fine, and subsequently traced it back to the comms room. At this point I was unsure what the problem was, so decided to replace the 24 port 10/100/1000 netgear switch they were using out of hours (we have a spare). I haven't done this yet, because...

- The next day another room lost connectivity. They were going through a similar netgear, only this one was a 10/100 so slightly older. At this point I decided to power down and then power up this second switch. All connections subsequently came straight back online. No problems since.

Architecture:
Each room's switch is plugged into a Layer 2 gigabit master switch. Servers and NAS boxes are plugged into the master. Total number of switches is 4 (layer 2, 2x24port netgears, and 1x 48 port netgear). We also have our VoIP traffic on the same LAN, which  goes through a separate subnet (255.255.0.0). We have approximately 100 workstations and 40 IP phones. 2000 domain.

Question;
Any advice on where I could look to start tracing the cause of the problem? The only 'event' that coincided with both outages was the set-up of a brand new Dell laptop. I dismissed this though, we do this frequently and I can't see where it would cause a problem?

Thanks in advance,
Chris.

Answer : Why are batches of users losing LAN access?

Sometimes yes because there internal tables become corrupt. Can happen for many reasons. Also you may have had a bad NIC on the network that caused issues. In managed switches generally you can force a rebuild of there tables. You can also control many other things such as speed duplexing etc... You can also see the current status, for example you could have a bad nic on a pc that is only communicating at 10mbps but the switch is at 100mbps or the card is communicating full duplex and the switch is set for half. These types of issues can cause problems with the switch.

I have had to power cycle many of the unmaged personal switches after a period of time due to problems like this. This is why managed is better you have more control over the switch and can see what is going on unmanaged you are at the mercy of the switch deciding what is best.