Vlans, arp and DHCP addressing

[chazk1]

I have a couple of 12-port fibre Cisco WS-C3750G-12S-E switches which have Catalyst 3550 clusters patched into them.
Each 3550 Cluster has been allocated a seperate Vlan.

I have physically moved 6 x PCs, which use DHCP to obtain their IP addresses, from one cluster (vlan 10) to another cluster (vlan 12). When booted the PCs will not connect via the new Vlan.

I've checked the clustered ports and they show as connected. Having the mac-addresses I checked the arp table on the 3750 switches and they still show them as having been allocated the old Vlan IP addresses.

Is there anyway I can correct this on the switch so that they pick up an address on the new vlan ?

If I set the new switch ports to 'switchport access vlan 10' they will work.

 

[robertjo24]

Did you try a release and renew on the machines?

 

[chazk1]

Yes thanks, released, renewed and rebooted.Still picks up IP address it obtained when connected to the previous LAN.

 

[vipergg]

Where is the dhcp server ??? Are other pcs on vlan 12 getting addresses ok . If the dhcp server is on vlan 10 do you have ip helper addresses on the interface for vlan 12 ????Also make sure the new ports on vlan 12 have portfast turned on .

 

[ADB100]

This sounds like you may have DHCP SuperScopes setup? If you have then you need to get rid of them since this isn't what SuperScopes are intended for.
Superscopes are generally used when you have a router with secondary IP addresses on its LAN interfaces.
Can you post any configs, it might help us help you a bit more?

Andy

 

[chazk1]

Reply to last 2 messages.
The DHCP server is on a separate vlan - lets say vlan 2
Yes, other pcs on same vlan are obtaining addresses.
IP Helper address of dhcp server has been configured for each vlan.
Spanning-tree portfast already enabled on each port.
I'm checking with the server team re: superscopes

 

[chazk1]

Reply from our server team:

There is a bug with the DHCP service that when the server is rebooted the scopes go back into a Superscope config which prevents ip addresses from being corrected if a machine moves floors.

They are looking for a long term fix, maybe using a core switch as a DHCP server.

Thanks all.

 

[ADB100]

What servers are they? I have both windows 2000 & 2003 servers running as DHCP servers and I have never seen this. Are you sure they just haven't configured SuperScopes and are trying to fob you off since you have found a hole in their configurations/design?

Andy

 

[123tech]

Have you setup a new scope for VLAN 12? I have a similar setup, but for each vlan we have a scope that falls in that IP address scheme, but we are not using super scopes. Example, Vlan 10 might have dhcp for network 192.168.10.x/24 and Vlan 12 woudl have dhcp for 192.168.12.x/24. Not sure if that helps, but that's how I have it.