Configuring DHCP relay agent

[gbkeku]

I'm kinda confused. I want 3 remote locations to communicates with CUCM . So I decided to use IP Helper.

I have 4 Routers. HQ router R0, and Remote Routers; R1,R2,R3. CUCM is connected to the Core Switch in HQ. 

DHCP Server is configured in Core Switch in HQ and in R2, R3.

I made 4 sub-interfaces on R0 (Gi 0/2.110 encapsulation dot1q 110; Gi0/2.115 encapsulation dot1q 115; Gi0/2.113 encapsulation dot1q 113 and Gi0/2.20 encapsulation dot1q 20) and switched Gi 0/1 of Distribution Switch to trunk mode  which  connects the remote locations.

Also, I need to configure a DHCP-relay agent on Router1, R2, R3  so R0 could give addresses from pools for VLAN 20.

But I don't know, which interface I should configure IP Helper in R0, R1, R2 and R3, which addresses I should add to ip helper-address on sub-interfaces.

I would really appreciate your help!

[Georg Pauwen]

Hello,

The IP helper addresses (the IP address of the DHCP server) have to go on:

R1
Gig0/1

R2
Gig0/0

R3
Gig0/1

[gbkeku]

Thanks your response. Am I not suppose to configure it on the VLan 20.

[pieterh]

DHCP requests are broadcasts and by default not routed by routers
an ip-helper transforms broadcast to unicasts, so it can be routed to the destination

so to relay/route requests from the client to the dhcp server in another subnet you need to configure relay agent.

you configure it on the routed interface facing the client. and you configure the ip-adress of the dhcp-server as destination for the ip-helper. previous poster pointed the routers and interface where to do this, but it is incomplete,

your diagram is inconsistent: the drawing reads Gi0/1 to the client switch and Gi0/2.10 and gi0/2.20 as subinterfaces

if Gi0/1 is correct I expect also Gi0/1.10 en Gi0/1.20 as subinterfaces to the client switch

then R2 -> Gi0/1.20  and R2 -> Gi0/1.20 need an ip-helper to reach the DHCP server for the voice pool

Core2 is a L3 switch? but I see no subinterfaces there

You do not use DHCP for the PC's?

if you do, you also need ip helper int R2 gi0/1.10 and R3 gi0/1.10 and a second pool for the PC's

all ip-helper configuration lines point to the dhcp server (core1 / 176.16.17.6)