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New Member

Multiple VLAN - DHCP problem

I am having trouble getting my Server2000 DHCP server to generate the correct IP according to the VLAN to which the client belongs. We are using 3550 24port powered switches on the access level and a 3550 12-T and 12-G on the core level. We have set all necessary helper-ip's and the clients receive a correct IP the first time they join the network but after their VLAN is changed it continues to try and assign their original IP. If the DHCP scope is disabled then it will reassign the correct scope's IP. We have experimented with Option82 and have still not determined if we need DHCP service running on both the access and core level.

4 REPLIES
Purple

Re: Multiple VLAN - DHCP problem

You only need the helper addresses configured on the switches or routers where the subnet is defined .

New Member

Re: Multiple VLAN - DHCP problem

Yes, that is what is happening. The helpers are configured on the L3 VLAN's in the 3550-12T.

New Member

Re: Multiple VLAN - DHCP problem

Have you checked the lease time of the IP address allocated ?

Prior to changing VLAN is the DHCP address released.

Purple

Re: Multiple VLAN - DHCP problem

Check to see if you have a specific broadcast address in the vlan definition , if so get rid of it and this might fix your problem .There should not be any specific broadcast address defined on the vlans . We had the same type problem where we defined a specific broadcast address xxx.xxx.xxx.255 and hsrp would not work correctly if the person moved to a different vlan . Remove the defined broadcast address and let it use the default of 255.255.255.255 . Very good page on dhcp at

http://www.cisco.com/en/US/customer/tech/tk648/tk361/technologies_tech_note09186a00800f0804.shtml

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