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Is there a way I can set a DHCP on the 3.0 network without using a server like the other two networks or configuring a DHCP on the router?

Can I use the IP helper-address command to use the server on my 200.0 network for DHCP?

enter image description here

  • I think we're missing a picture. – Ron Trunk Oct 12 '15 at 13:07
  • Your right sorry. Lol! – user17715 Oct 12 '15 at 13:21
  • The network to the far left is 1.0 middle network is 2.0 and the far right is 3.0. Excuse the blur. – user17715 Oct 12 '15 at 13:22
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 12 '17 at 19:12
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Yes, you can. That is exactly the scenario it was made for. On the far right router (the 3.0) network, use the help command on the LAN interface. For example:

Interface Fa0/1
ip address x.x.x.x m.m.m.m
ip helper-address y.y.y.y

y.y.y.y is the IP address of your DHCP server.

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  • Do I use the helper-address command somewhere? – user17715 Oct 12 '15 at 13:25
  • I expanded my answer. – Ron Trunk Oct 12 '15 at 13:29
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DHCP uses Broadcast to find a DHCP server. ip-helper may be used on your router to forward those broadcast frames to your DHCP server located within another broadcast domain.

The router receives the broadcast frame and uses unicast to forward it to the specified dhcp server.

Ron has already posted the correct configuration required to set up DHCP helper where the interface can be a physical interface a sub-interface or an SVI.

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It can be done but it's not really recommended. You just have to make sure your server has a scope for that network so it knows which pool to use when it reads the relay stamp and configure the helper on the local router (don't configure multiple devices with helpers, it's a really common mistake to see).

Best practices rant:

When possible you should do DHCP as close to the originating network as possible, if a WAN link goes down they're not going to be able to access any of the information locally. If the .200s site link goes down any sites relying on that server have lost access to every thing until you go around and statically configure addresses on devices that need it.

Typically you'd use helper if you have multiple subnets at the same site (or layer 3 boundaries? I can't tell exactly what's going on in your screenshot, it's small and my eyes are strained currently)

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