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Community Member

DHCP problem on Catalyst 5000

We have a very strange problem. At the customer site, when somebody wants to get an ip address via DHCP, it is no problem. When somebodyelse from another site wants to log in they don't get an ip address. They have to do a release and a renew to get an ip address.

When we put a hub between the laptop and the catalyst there is no problem to get an ip address. We toke a trace via portmirroring, we didn't see any dhcp pakket. When we toke the very same trace via a hub we saw some dhcp packets. So it seems to me the catalyst "looses" somehow these packets

all PC and Server are on the same Vlan on the same Switch.

all local users can get an ip adress. People who come from an other site

and want to login don't get an ip address.

All ports have trunking off, channeling off, portfast on.

Does someone have an idea for this problem??

Tx.

6 REPLIES
Blue

Re: DHCP problem on Catalyst 5000

Do you have an ip helper address in your config?

Community Member

Re: DHCP problem on Catalyst 5000

No we don't have ip helper on our config. Do you have any idea what it could be??

Blue

Re: DHCP problem on Catalyst 5000

From what I gather from your problem, people at your site, which are all in the same VLAN, are able to get IP's. However "offsite", which I am assuming someone connected by a frame-relay connection, etc. needs to get there IP address from you DHCP server. Since those clients are on a different segment, subnet, the ip helper command needs to be entered into the router. The command "ip helper-address xxx.xxx.xxx.xxx) where the ip address is the address of your DHCP server. You must also create a new scope for those clients on your DHCP server.

Community Member

Re: DHCP problem on Catalyst 5000

The "offsite" users are people who come from another site with their laptop and try to connect to the domain. They don't get an IP address if we put them on the switch but they receive an IP address if we put an hub between the switch and the users. I don't understand what can go wrong here? Directly to the switch it doesn't work but on a hub connected to the switch it works perfect.

Community Member

Re: DHCP problem on Catalyst 5000

The TAC engineers told us there was nothing else they could do. They don't know what could cause the problem so I wondered if someone already had this kind of problems?

Community Member

Re: DHCP problem on Catalyst 5000

did you try to disable spanning-tree (don't use portfast)

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