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New Member

VLAN Issue

Hi all ,

I have a question regarding VLANS and DHCP server.

I have a Cisco 3750 as a core L3 Switch

I create the 4 VLANS ,vlan 76 ( Vlan 77 , Vlan78 and Vlan 81.

I associated one port to Vlan 76, one to Vlan 77 one to vlan 78 and remainimng to Vlan 81 ( DHCP and all other servers are in VLAN 81)

On VLAN 76 vlan 77 and VLAN 78 ,i connected L2 Switch ( all ports of the switch are on same VLAn respectively)

I have set the IP helper address on each VLAN.

Now when i first cconnect the PC to VLAN 76 DHCP server issue the Correct IP to the PC( 172.16.76.X) now when i removed my PC from Vlan 76 and plugged into the Vlan 78 MY PC again get the Ip address from VLAN 76 , where as it should get IP from Vlan 78 ( 172.16 78.x)

Could you please help me in resolving the problem?

Below is the configuration of the port assosiated with VLAN 76

Interface GigabitEthernet1/0/2

description Connect-to-SegmentA

switchport access vlan 76

switchport mode access

switchport nonegotiate

interface Vlan76

description SegmentA-Vlan

ip address

Ip helper-address is the DHCP server.

I want that DHCP should issue the ip address according to VLAN.


Looking for help

  • Other Network Infrastructure Subjects

Re: VLAN Issue

Have you created an 'interface vlan78' ? If you have, and if you have given it a 172.16 78.x address, then the DHCP server will assign it an address out of the 172.16 78.x range, providing that you have created a scope on the DHCP server for the 172.16 78.x network.


New Member

Re: VLAN Issue


Thanks for answering

yes i have created the Interface

interface Vlan78

description SegmentC-Vlan

ip address

ip helper-address

also 172.16.78.x scope has been created in DHCP server for distribution.



Re: VLAN Issue


Can you confirm that you did a DHCP RELEASE on the PC before trying to acquire a new address when you plugged it into a VLAN 78 port ?


New Member

Re: VLAN Issue


yes I confirm you that i first release the DHCP lease by IPCONFIG/release

But reslult is same.

Attached is the Config file for core L3 switch and HP L2 2650 switches.

Please help me on this issue.


Re: VLAN Issue

Verify your DHCP scopes are defined correctly. If you defined a separate scope with separate router default gateways then your clients should allocate according to VLAN.

New Member

Re: VLAN Issue

make sure you are not using superscopes that was my issue on a problem like this.

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