use of IP helper address

[ahmadbilal]

hi,

i have a DHCP server x.x.x.x running in my LAN i want my remote office lan to get IP addresses from my DHCP server.I have applied IP helper address x.x.x.x on the lan of my remote office and on the serial of this office.

Still i remote office users dont get IP addresses.No access-lists are in place and i have also defined ip forward-protocol udp in the routers.

How do i test if a request for DHCP is coming to the remote router lan interface.i tried enabling debug ip udp but dont see a request for udp port 67.My both routers are running OSPF.

regards

[Georg Pauwen]

Hello,

can you post the configurations of both routers ?

Regards,

Georg

[ahmadbilal]

Following is the config of remote router.Is debug ip udp the right way to check if any messages are being recieved.

REMOTE:

version 12.2

service timestamps debug datetime msec

service timestamps log datetime msec

service password-encryption

!

ip forwrd-protocol udp

ip subnet-zero

interface Loopback0

ip address 10.1.1.1 255.255.255.255

!

interface FastEthernet0/0

ip address 10.2.2.1 255.255.255.0

ip helper-address 10.4.4.30

duplex auto

speed auto

!

!

interface Serial1/0

ip address 10.3.3.2 255.255.255.252

!

router ospf 20

log-adjacency-changes

network 10.0.0.0 0.255.255.255 area 20

!

ip classless

line con 0

line aux 0

line vty 0 4

login

!

!

end

[Harold Ritter]

Debug ip udp on the router configured with the "ip helper-address" should give you some information on what is going wrong. You configuration looks good. Make sure 10.4.4.30 is reachable and that it is configured with a scope of 10.2.2.0/24.

Hope this helps,

[Richard Burts]

I think that your config looks mostly ok. I would suggest that you remove the command:

ip forwrd-protocol udp

This command is expected to specify protocol port numbers not just UDP and I am not sure what the effect is of what is essentially an incomplete command. And forwarding of DHCP is enabled by default so you do not need any ip forward-protocol command.

If you want another idea of how to test, I would suggest a test on the router on the subnet where the DHCP server is connected. On that router I would use debug to look for packets coming to the server. To do it I would do this:

config term

access-list 190 permit ip any host 10.4.4.30

end

terminal monintor

debug ip packet 190

You might need to put the command no ip route-cache on the interface to force the router to process switch the packets so that debug will see them.

This debug will show any packets being forwarded to the DHCP server.

Are you certain that the DHCP server is properly configured with a scope to respond to PCs on your segment?

HTH

Rick

[smif101]

One thing to check is to make sure that your DHCP server has a scope in it for the 10.2.2.0 network. If it does and everything still doesn't work you can always use your router as the DHCP server just the same. Here is a sample config

R4(config)#ip dhcp excluded-address 10.2.2.1 10.2.2.10

R4(config)#ip dhcp pool dhcpsrv

R4(config-dhcp)#network 10.2.2.0 255.255.255.0

R4(config-dhcp)#default-router 10.2.2.1

R4(config-dhcp)#dns-server 150.50.4.10

R4(config-dhcp)#domain-name smif101.com

[m.saufi]

Smif010,

Pardon me to interrupt, when configuring dhcp server in the router, does this mean that you can go without the Windows dhcp server? What I'm trying to say is that can the router be a DHCP server by itself?

Many thanks.

[net_wiz73]

why have u entered the ip helper on the serial interface of your LAN router. It is not required as the remore router is the one which needs the helper. try removing that line frm your main office router.