Some clients on 2950 switch can not reach dhcp server

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Nov 3rd, 2005
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I have several clients connecting to a 2950 switch that can not reach the dhcp server. The 2950's connect to the 4506 core switch via dual fiber. The 4506 handles intervlan routing and has the ip helper address defined in it. There are possibly 10 clients out of 150 that can not hit the dhcp server. The have portfast enabled and are hard coded to 100/full. Please let me know if you have any ideas.


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thisisshanky Thu, 11/03/2005 - 10:26
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If you configure a static address from that subnet on the PC's not hitting the DHCP server, can they ping the DHCP server ?

Are there devices on the same vlan , on the same 2950 switch, that does get DHCP ? (Some of them get, while some of them doesnt ?)

I would take a look at configs on the 4506, and also the 2950 in question.

glen.grant Thu, 11/03/2005 - 10:53
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I have seen some older clients that have a problem even with portfast , use the "switchport host" command which will turn on portfast ,shuts off trunking and channeling to bring up the port even faster than with portfast alone. something easy to try . Make sure the clients nics are hardcoded to 100/full ,can't hardcode the switch 100/full without hardcoding the clients nics 100/full also.

William Maguire Thu, 11/03/2005 - 14:45
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I gathered some additional information:

The clients are all using IBM thinkpads t41 and t40. The issue is on other model switches as well. The issue is on multile vlans (if I set a port that was in vlan 100 to vlan 100 or vice versa it corrects the issue). I'm really stumped now.

William Maguire Thu, 11/03/2005 - 14:46
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(if I set a port that was in vlan 100 to vlan 200 or vice versa it corrects the issue

Richard Burts Fri, 11/04/2005 - 07:51
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It sounds to me like there may be an issue with the way that some of the VLAN interfaces are configured. Can you post configuration of the VLAN interface for the VLAN in which clients are working and also post configuration of the VLAN where clients are not working?

Also when you get into one of these situations, if you disable the switch port to which the client is connected and then enable the port does it change the behavior?



andrew.butterworth Fri, 11/04/2005 - 10:54
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Do these users move around the network? i.e. they can connect to ports in VLAN 100 or 200 depending on where they plug in? Do you use SuperScopes on your DHCP server and the scopes for VLAN 100 & 200 are in the same SuperScope?



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