Regarding DHCP

[ncnaveen_arasu]

Dear team,

If we have two routers A (NOC)  & B (Remote office), and we want to configure the DHCP server behing router A so that clients in LAN segment of router B should be able to get the Ip address via DHCP.

Once we set up a DHCP server in NOC, what needs to be configured in Router/Switch to allow DHCP requests and to make it work.

Please suggest.

Thanks in advance.

Naveen

[Jeff Van Houten]

You need an ip helper address pointing to the "closest" interface connecting router a to b. the helper address should be installed on the router b interface used by your dhcp clients.

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[Jeff Van Houten]

I misread. If the dhcp server is standalone, just use ip helper pointed to it. Install on LAN interface of router b.

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[ncnaveen_arasu]

HI Jeff,

Thanks for the information, We have tried the IP helper address in LAN interface of remote office Router B. but its not working.

In our NOC, remote office will get connect to GSR(NOC router router, then L3 switch, then L2 switch then the system where we hosted the DHCP application. So in this set up when we enabled Ip helper address in LAN interface of router B, it's not working.

Please advice any additional commands need to be enabled in the L3,L2,GSR as well.

Thanks & Regards,

Naveen

[tsiarnouski]

Hi.

You should use "ip helper-address" i think. I had some free minutes at my job and i've done simple gns3 emulation regarding your situation( as i understand it from your description). But it is without any vpn and so... if you have vpn between offices you should add exception in ACL.

       Everything work in my topology. R1 recieves ip address. In case of R4 backward route to R2 you should have default-gateway on DHCP server.

       Try to ping dhcp server from router B to be sure that you have l3 connectivity.

[ncnaveen_arasu]

Hi Stanislau,

Thanks for the reply, We are running MPLS and IBGP for VRF network and OSPF as IGP, We have end to end reachability if statis IP has been assigned. So wether it is a problem for blocking DHCP requests.

We used ip helper-address on LAN interface of router. and allowed ip forward protocol UDP (67 and 68 ports) but its not working.

In  LAN we have created sub interfaces for diffrent VLANS. SO we need to apply for physical interface of subinterface.

Please suggest.

Regards,

Naveen