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New DHCP server is not working across switch

We are replacing our DHCP server and have come across a problem I'd like expert advice on.
- Our current DHCP servers (DC1,DC2) are providing leases without issue.
- We have configured new DHCP server (DC3, DC4) to replace these servers.

After deactivating scopes on DC1/2 and activating on DC3/4 we are finding the following (after ipconfig /release & renew);

Clients on the same subnet as DC1/2 obtain leases as expected

Clients on a separate subnet/switch timeout when trying to contact a DHCP server, respond OK once DC1/2 scope is re-activated

I have checked a related switch and there is no ip-helper command configured. My question is - can anyone explain why this would work with DC1/2 and not DC3/4?

Thanks in advance

SOLUTION

Paul MacDonald

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agradmin

ASKER

I don't see anything configured on the related switch.

Paul MacDonald

There must be something if these are actually two different subnets. How do clients on the foreign subnet find the DHCP servers? Or are the DHCP servers multihomed?

Ken Boone

Is DHCP snooping configured on your switches. DHCP snooping will allow dhcp responses to only come from an authorized port. This prevents someone from putting a rogue DHCP server in place. If DHCP snooping is configured then you need to configure the authorized ports.