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Wrong DHCP Addresses


I'm having trouble with clients getting the wrong DHCP addresses. It is isolated to one location. The problem is that clients on VLAN 3 are getting addresses for clients on VLAN 1. Now it is not all clients and it is not every time. Sometimes they will get the right address sometimes they will get the wrong one.

Any help would be great.


6 Replies 6



Where is the DHCP server located. DHCP server is layer3 switch or router? Is that a Windows server.

Please paste the config and a brief diagram.

-amit singh

The DHCP server is located on VLAN 3. It is a windows DHCP server.

I've attached the sh run from the 3750 connected to the DHCP server. The server is located off of gigabit 1/0/3.

Thank you for your help

I can see that under vlan1, you have 2 helper address while under vlan3 only 1 helper address is configured.

interface Vlan1

description High School MDF

ip address

ip helper-address

ip helper-address

no ip redirects

ip directed-broadcast


interface Vlan3

description High School Wire Room D1

ip address

ip helper-address

no ip redirects

ip directed-broadcast

what are these 2 IPs and ?

are both DHCP servers ?

I would suggest to try to configure only single IP helper address unless you are using multiple helper address for UDP servics other than DHCP.

let me know if it helps or u have questions.

The address is another server which needs broadcasts to be forwarded. it is located on VLAN 3. The ip helper-address on VLAN3 was causing the issue. The DHCP server is located on VLAN3.

Your help has been much appreciated.

are all clients in VLAN 3 having same problem or only few clients have this problem?

can you check the edge switch port config to which clients in vlan 3 are connected ?

if u r connecting client PC only to a single port then port should be configured as access port.

also check for correct vlan membership of the port to which clients are connected. they all should be member of vlan 3.

if possible paste the config of one of the switchport connecting to client having problem.

All the above steps mentioned are worth trying. However if it still does not solve the problem try disabling spaning tree if you can and see if the problem still persists


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