DHCP request through accesspoint and router

[joris_struijk]

This is how our setup is like:

Laptops => Cisco 1100 AP(static IP) => Wired LAN (Subnet 1) => Cisco Router => Wired LAN (Subnet 2) => DHCP server

What i would like is that the DHCP-request from our laptops is forwarded/relayed through the AP and Router to the DHCP-server and back.

We dont want to use the AP's internal DHCP server but centralise this.

At the moment i'v configured the AP through CLI and added the following command: ip dhcp-server xx.xx.xx.xx

Where xx is the IP of the DHCP server

On the Router i'v added the command ip helper-address xx.xx.xx.xx

Where xx is the IP of the DHCP server

Don't know if this is the correct way, but i do know it isn't working.

Some help is realy appreciated.

Grx,

Joris

[joris_struijk]

We narrowed it down to the Windows 2003 acting as router.

We temp. replaced this windows router with another cisco router and then it works.

Wen we then place back the windows router it stops working.

The windows router doesn't correctly routes the Cisco's DHCPdiscover,DHCPrequests etc...

Now what??

We must be doing something wrong on the windows router but what?

[joris_struijk]

what is the meaning of "no ip directed-broadcast"?

we disabled this but to no result

[joris_struijk]

I'v run Ethereal on the Windows router and it shows the following:

Broadcast from Cisco Router, Protocol ARP, Info: Who has 10.6.0.2? Tell 10.6.128.1.

Reply on interface loop from the Cisco Router.

On the other interface he gets an ARP reply from the DHCP server responding that the DHCP server is located at the 10.6.0.1 interface of the Windows router

10.6.0.2 is the IP of the DHCP server.

10.6.128.1 is the interface of the Cisco router connected to the Windows router.

Now what? The Windows ROuter isn't forwarding anything back to the Cisco router.

[kka]

Why does the Cisco use ARP for an IP address (10.6.0.2) of

a subnet it's supposedly not part of? This I would expect if

the Cisco is configured with a netmask containing both IPs

10.6.128.1 and 10.6.0.2, i.e. 10.6.128.0/16

Without prefixes/netmasks it's a bit difficult to understand

your network.

Yesterday you wrote, that ping from the client to the server

(DHCP server?) works in both directions - is this for the

same setup?

[joris_struijk]

I am seeing ARP requests for the 10.6.0.2 IP from the Cisco Router and nothing else. Why?

[fausto-oliveira]

Are you sure that the windows router is forwarding between interfaces ?

Do "netsh routing ip relay" followed by a show global and paste the output here.

Also do "netsh routing ip dump" and paste that output.

[joris_struijk]

It's working right now.

Thx for all the help, i'v learned a lot from all of you.

The windows router had a problem with one of the interface, replacing it resolved the problem.

Silly problem, difficult to trace.

Grx and all the best,

Joris