DHCP/Login Issue

May 17, 2006 3 Replies
J

Hi,



We are having an issue with DHCP and login to a Novell server whereby the clients can't find the tree. There seems to be some sort of timing issue when a computer boots, when the port on the switch becomes active and when the computer receives an IP address from the DHCP server.



We thought that we had established a procedure whereby users could login 30 seconds after seeing Ctrl-Alt-Del. I'm told that some users have experienced problems even after 2 or 3 minutes.



We have found out that if you try to login too soon it is possible for the computer not to have an IP address. If you then login to the local Windows machine (as opposed to Novell) and issue the appropriate dhcp release/renew commands, the IP is established. Then you can connect to Novell. However, this is too difficult for the average user as you might imagine.



Does anyone have any suggestions on how we can eliminate this issue? Is there a way to guarantee that the IP address is established before Ctrl-Alt-Del is displayed? Do you think there is some other issue going on that we are not considering?


Environment:


- Core switches = Cisco 3750 (qty = two)



- Access switches = Dell 5324 (qty = ten)



- Client machines = Windows XP SP2



All of the access switches are connected to both core switches. The DHCP servers are running on the core switches. The DHCP scope is split in half so that there is no conflict with IP addresses. There are 7 VLANs of which 4 are setup for DHCP.



The access ports (as opposed to trunk ports) on the Dell switches are configured with "spanning-tree portfast".



All of the above is known internally as the new network as is running on 10.x networks.



There is also an old (or current) network running on 192.168.x networks. The two networks are linked by a single cable running from one of the older switches (a Dell 5224) to one of the core switches. There is routing between the 10.x and 192.168.x networks, but I'm reasonably sure that no VLAN is passed back/forth. There is a DHCP server running on the old network on a Windows 2003 box, but the scope is only for the 192.168.x networks.



Thanks,


- Joe



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T

Make sure all of your ports are configured with "spanning-tree portfast" What is happening is that your PC's are booting, the NIC is enabled and switch port comes up. Since portfast is NOT enabled, the port goes into blocking state for 30 seconds, so no traffic passes, and the PC won't get an IP address. "spanning-tree portfast" on the switch tells the port to start passing traffic immediately without waiting the normal 30 seconds to determine if a another spanning-tree device is on the other end. You should not enable this on ports that connect to other switches.

On Windows98, NT and 2000, this problem was very rare because the boot up time of windows was much slower and the time elapsed between the NIC coming on and requesting a DHCP address was much longer.. XP boots pretty quick and this is a very common problem.

Scott

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T

Make sure all of your ports are configured with "spanning-tree portfast" What is happening is that your PC's are booting, the NIC is enabled and switch port comes up. Since portfast is NOT enabled, the port goes into blocking state for 30 seconds, so no traffic passes, and the PC won't get an IP address. "spanning-tree portfast" on the switch tells the port to start passing traffic immediately without waiting the normal 30 seconds to determine if a another spanning-tree device is on the other end. You should not enable this on ports that connect to other switches.

On Windows98, NT and 2000, this problem was very rare because the boot up time of windows was much slower and the time elapsed between the NIC coming on and requesting a DHCP address was much longer.. XP boots pretty quick and this is a very common problem.

Scott

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J

Thanks for the reply. I believe I did mention that we are using "spanning-tree portfast" on the ports for the clients (PC) computers. Or did you mean something else?

Meanwhile, we may have solved the problem by upgrading our Novell client to the latest version.

Novell Client for Windows NT/2000/XP v4.91 (Recommended) File Name Document Title Creation Date nc491sp2.exe Novell Client 4.91SP2 for Windows2000/XP/2003 10JAN2006

- Joe

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