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Pls help on DHCP issue in C6509 network


Our network is separated to several vlans by Cisco 6509. at first we faced problem on DHCP IP address getting during bootup after releasing IP. thanks to Steve the problem was solved using portfast command - refer to following attachment.

Now we still face further issue related to it: Don't release IP first but keep the original IP, then when the client is changed from vlan A to vlan B, they can not log on the network, should first release IP, then renew IP, then relogin to the domain. In addition if use winipcfg to renew IP before release, the system will hold. Re: if only change the port profile from vlan A to vlan B without disconnection of cable, and the system reboot (not turn off power and on), the logon can work, another IP is got - in any other case it failed if not release IP first.

It's confusing us, appreciate for help.



=== attachment for last issue solved ===


Our network is separated into several vlans by Cisco 6509. DHCP service is supported by one NT server in Vlan1. Now the client which connects to Vlan1 port can not get IP address after releasing IP using WINIPCFG, even rebooting. But when in windows98, use WINIPCFG to renew, the IP can be got.

For other clients which have not been connected to Vlans, they connect to the normal HUB which shared with the DHCP NT server. After releasing IP, they can get IP using rebooting.

Re: for other vlans which are different from Vlan1, the clients can not get IP after rebooting. But they can get IP through winipcfg renewing. (the other vlans have been configured to use DHCP IP POOL which is the function of cisco6509)

We are confused on it and the users will be impacted if put them to Vlans as they would be frustrated to use WINIPCFG during boot up of the system.




Nov 12, 2001, 3:48am Pacific (1.)


it sounds like perhaps the DHCP requests timeout before the switch port is in an STP forwarding state.

Have you configured 'portfast' on user ports to speed-up STP process ?

Another option (depending on you sw version) is to configure 'set port host' which is a macro-command disabling certain parameters such as trunking/channelling and enabling portfast in effort to get a user port up and forwarding asap.

Important to note is that these commands must -only- be used on single *user* ports please see the following URL for more info:

Hope it helps



Nov 12, 2001, 5:50pm Pacific (1.1)

Hello, Steve

The problem was solved after setting spantree portfast to the user ports. very appreciate for your kind help!

Hi MickPhelps,

Only one vlan uses NT DHCP, others are using DHCP server on Cisco6509.



Community Member

Re: Pls help on DHCP issue in C6509 network

Win9x DHCP client is a very manual process. It might be easier to teach your users to shut down before restarting on the new VLAN than using winipcfg. Win2k And XP handle this much better by considering each network disconnect as a (most-likely) release.

Community Member

Re: Pls help on DHCP issue in C6509 network

Thanks, but how can I put a script in windows95/8 startup to let the IP first be released then renew BEFORE the NT login window appears.

As I tried to put the command in STARTUP setting, it only executed after login window appears... so it does not work.


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