Intermittent lost network connectivity on individual work stations

[moodymutey]

I manage a small-hospital computer network.  Next to the hospital there is an attached doctor's clinic with about 10 computers, all using windows XP.  Those computers are hard wired to a Netvanta 1234 managed switch which then feeds through a single cable to a Netvanta 1534 switch in the main server room.  The problem is that intermittently, infrequently, individual work stations in the doctor's clinic seem to lose their network connectivity.  The particular work station won't connect to the internet, won't connect to the network printers, and generally seems cut off from the network.  Nothing I do during this time period seems to have any effect.  After 20 to 30 minutes, the work station spontaneously returns to normal operation.  The machines have Vipre antivirus protection and Vipre is not finding anything related to this problem.  I have also run Malwarebytes antimalware and come up with nothing.  Because this phenomenon has never happened anywhere else in the hospital but has happened to many of the workstations in the clinic, I assume it must be occurring in something that is common only to the doctor's clinic computers, which is why I am wondering if the Netvanta 1234 could be involved.  I have talked to Adtran TS and they suggested this could be related to name vs. mac address conflicts.  I have only recently started monitoring the 1234 event logs so have not yet had the opportunity to check its logs after the problem has occurred (don't we love the intermittent problems).  DHCP is turned off in the 1234 and is handled by the server in the main computer room which is also the DNS server.  Anybody experienced anything similar?

[Anonymous]

- Thanks for posting your question on the forum. I would say we first need to figure out what state the PC is in when it loses network connectivity and also see if the switch correctly knows where the PC is in the network. Here are some things that would be helpful to know:

- Does the PC have an IP address and Default Gateway assigned when it is in this state? The output to "ipconfig" within the PC's command prompt window will answer this question.

- If the PC does have the correct IP and Default Gateway, is the PC able to ping its default gateway? Is it able to ping any device within its network? Is it able to ping out to the internet (i.e. 4.2.2.2)?

- Is the 1234 currently running a single VLAN? If so, try pinging the PC from the 1234 and the view the "show arp" and "show mac address-table". Within the "show arp" table, you will want to see if the IP address of the PC is matching up with the correct MAC address of the PC. If the 1234 is unable to resolve the MAC address, this is important to note as well. Within the "show mac address-table" output, you will want to make sure that the MAC address of the PC is listed only once and that it is linked to the correct switchport.

- It would also be good to try the above test with the 1534 as well.

The answers to these questions will help in narrowing down where the issue may lie. It may also be good to view the switchport statistics along the path the PC takes in the network to its destination.

Let us know if you have any further questions.

Thanks,

Noor

[moodymutey]

Thanks for the suggestions, Noor.  As I said in my post, I can only be in

waiting mode until the next time this intermittent problem strikes.  When it

does, I will follow your suggestions and then post again.

Ben Pressman Head of Maintenance & IT, Safety Officer

[moodymutey]

So, approximately a year later, I realized this post is still open.  What happened is that the intermittent problem went away.  I never got the chance to implement Noor's suggestions.  Therefore I am closing the case without knowing what was really going on.