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Loss of TCP Connectivity

This is an interesting problem. I work at a local college, and we have around 3000 users. Each residence hall, 10, are split into separate VLANs. Giving the whole layout of the network could take forever, but this is a summary. The problem is that roughly 400 students have been losing TCP connectivity after 5-10min. Say a computer turns on obtains an IP, can go on the "internet", sign onto AIM and everything else. Five minutes later they will still have a valid IP address, but be unable to browse and web pages, they will retain the ability to be signed onto AIM. While having the problem a student can still release and renew a valid IP. When pinging WAN hosts,, it will resolve the DNS but it will not respond. A restart of the computer will fix the problem 99.9% of the time. We have recently replaced our core routers with 6509 series with HSRP, and Spanning Tree, and around that time we started experiencing this problem. We have captured packets for 24 hours of the computers which have had the problem, to no avail. We have also checked for any and all viruses, spy ware, and any suspicious activity, to find no patterns. The issue is that no other VLANs other than the Residence Halls have been having this problem. Is there something that we could be doing blindly, or some security feature that is disallowing these computers to stay connected? If anyone has any ideas, or is willing to suggest anything it would be a great help!

Thanks in advance

Nathan Brooks

VIP Purple

Re: Loss of TCP Connectivity


can you post the configurations of your 6509 switches ? Can you also post the output of the command:

show spantree vlan x

where x is the number of the VLAN on which you are experiencing the problems.