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New Member

Multiple subnets 1 dhcp server

Currently we are running in a switched network. Next month we are moving to a pure routed network. We currently have 1 dhcp server sending out addresses in our We want to take the /20 and break it up among the different floors to a /22 while still keeping 1 dhcp server. We purchased a cat4503, and will be doing intra VLAN routing.

We will be setting up different scopes for each subnet on the DHCP Server.

How can I be sure that a PC on the floor gets an IP that is correct for their scheme. Meaning if the PC is broadcasting from the how can I make sure it gets an adress in the scope and not the scope and therfore leave the PC useless because each scope will have a gateway assigned to it.

I hope I am making this clear.




Re: Multiple subnets 1 dhcp server


The only way to truly be sure is to check your DHCP leases and the PC but the way it works, it is pretty hard to mess this up. The Client sends out a DHCP Discover message (BCAST) the router (with ip-helper) will encapsulate this up with it's source IP (of the VLAN interface) and send the request off to the DHCP server. This VLAN source IP is how the DHCP server knows which scope to pull the address from. So if a DHCP Discover message comes in from Subnet A the DHCP Server will issue from subnet A ..

Hope this helps clarify,


New Member

Re: Multiple subnets 1 dhcp server

Perfect. I thought thats how it would work, but I needed to be sure. We have very little time from when we get the equipment in until we have to install it. Go figure. That was the only piece that I was missing.

Thanks for your help