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by rcoolman

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I have an NT4 domain. We are adding additional Cisco switches and want to split the network (due to size)into multiple VLAN's. My core switch is a Catalyst 3550-12T. I have created the VLAN's and all the switches recognize them. I have enabled routing on the 12T and if I manually set the IP parameters on a system on VLAN1 & VLAN2 they can ping. What I don't understand is how to set up DHCP on my NT server to serve the proper IP's to each VLAN. VLAN1 is 10.1.0.0/16 network and VLAN2 is 10.2.0.0/16. Can anyone help me set this up?

6 replies

by riverfreight

If I remember right you install a faux IP for each split in the originating hardware; Gawd, Call IBM for assistance as everyone I know of and know that knows how to do it correctly is dead or ancient to the point of and including clarity of mind only on occasion.
RIVER FREIGHT

by solis

Assuming you have your scopes configured correctly & your DHCP server supports it (ISC dhcpd with the shared-network clause works well), you will need some form of DHCP relay unless your DHCP server has an interface cabled to a port in each VLAN.Alternatively, you can specify "ip helper-address" on Cisco routers to forward specific broadcasts to a dedicated box. If your DHCP server was 10.1.0.47 in VLAN 1 you would configure the router's broadcast recieving interface thus:

router(config-if)#ip helper-address 10.1.0.47

ip helper-address forwards more than just DHCP broadcasts, so you need to read this:

http://routergod.com/trinity/

This is a nice breakdown in a comedic fashion & more...

Below is document specifically addressing your switch:

http://www.cisco.com/en/US/products/hw/switches/ps646/products_configuration_guide_chapter09186a008007e714.html#xtocid2281417

Have fun & good luck!

by solis

Clarification:

router(config-if)#ip helper-address 10.1.0.47

This command would reside on an interface cabled to VLAN 2, 3, 4 and so on, but not on the interface in VLAN 1 where the DHCP server resides.

Also, each scope must be configured to push down the correct default gateway for each VLAN.

by rcoolman

I couldn't get it to work the way I wanted, but appreciated the link to routergod. I also felt like maybe my situation couldn't work the way I wanted after working some more on it based on your reply. Solved problem by enabling dhcp on Cisco device & killing it on server. Thanks for help.

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