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DHCP Challenge

Mel Wade
Occasional Visitor

DHCP Challenge

I've just put in some procurve layer 3 switches.

I have 3 buildings that I service - Ad Building and two dorms. Dorms are connected to the Ad Buidling via fiber to procurve switches.
My current subnet is 10.0.4.0/22 with a gateway of 10.0.4.1 and DNS of 10.0.4.10

I need to VLAN so that each dorm and the ad building responds to a different (local) DHCP server at it's location but they remain on the same subnet.

AdBuilding - 10.0.4.1 to 10.0.5.254/22
Girls Dorm - 10.0.6.1 to 10.0.6.254/22
Boys Dorm - 10.0.7.1 to 10.0.7.254/22

The key task I need to accomplish is to have a separate DHCP server for each building, but have my content filter still see the actual client IP address so that it can handle authentication and reporting correctly.

I have to have separate DCHP servers so that I can run LTSP thin client servers in each building and have PXE booting work.

Any tips to ease the learning curve would be appreciated.
3 REPLIES
Thomas Joebstl
Frequent Advisor

Re: DHCP Challenge

Unless you configure your 'some procurve layer3 switches' to do NAT (which most dont support afaik) your content filter will always see the actual client IP.
Just dont forget to configure routes on it so it knows where to send responses for your dorm subnets.

You dont need separate DHCP servers, properly configured DHCP relaying on the L3 switch and a properly configured DHCP server can handle multiple subnets with different client options.
Mel Wade
Occasional Visitor

Re: DHCP Challenge

BTW I have ProCurve 5300xl Swithces.

I realize that it is possible to have one DHCP server, but having multiple servers would actually make management of the network easier in this case. Each dorm has a separate LTSP server. The clients PXE boot from the DHCP instructions. Without different servers I would have to create reservations for each client to be sure they booted from the correct LTSP server.

My concern is that if I setup separate VLANs for each dorm that the content filter in the main building will not see the client IP address in the dorm since they would be routed through the VLAN. Am I correct in this?
Thomas Joebstl
Frequent Advisor

Re: DHCP Challenge

You dont need per-client reservations, DHCP is smart enough to figure out which subnet the query comes from and assigns an appropriate address. You just have to make sure there's a subnet declaration with the appropriate values for each subnet. If DHCP relaying didnt work that way I'd have a really hard time administering my DHCP servers...

Routing doesnt alter any IP addresses so your content filter will see the clients as 10.0.6x or 10.0.7.x.