DHCP ip helper question

[dasmit]

Hello,


I have setup my router Back-to-Back, I setup a 2000 server running DHCP trying to get through the router to the client on the other side.

I have looked at cisco web site, all I saw to configure was the ip helper-address on the interface. I also saw something on the ip forward-protocol 68 and 67 for bootp/dhcp clients and servers.

I setup my router like this
DHCP server 150.150.1.2 255.255.255.0

router 1
E0 int on router1 150.150.1.1 255.255.255.0

ip forward udp 67
ip forward udp 67

S0 ip address 132.183.161.1 255.255.255.0
ip helper 150.150.1.2
encap hdlc
clock rate 64000
no shut

int on other router, which is a 2505 has 8 hub ports on it so no config is needed for the hub ports.

router 2
so ip address 132.183.161.2 255.255.255.0
ip helper 150.150.1.2
encap hdlc
no shut

I can ping the DHCP server fine, and I have been beating on this for a little while now, I am sure I am just over looking something.

Thanks in advance for the help!

 

[wybnormal]

IP helper goes on the side closet to the client.. DHCP works by the client broadcasting for a DHCP server.. any DHCP server.. the router picks it up the on the ethernet port and needs to know to forward it to where the server is at.. so the helper is on the closest port to the client.. the packet is repackaged as a unicast and forwarded to either the subnet (x.x.x255) or to a specific IP (x.x.x.123) Once the server gets the request, it returns an DHCP OFFER via a UNICAST packet.. the client BROADCASTs back and the the server sends a ACK UNICAST as the final packet. You can see what IP helper is needed only on the one side.. this does NOT hold true for NT authentication onto a domain, WINS etc..

THis document explains the DHCP side pretty well...

http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_c/ipcprt1/1cddhcp.htm

Here is another link that might prove useful.

http://www.cisco.com/univercd/cc/td/doc/product/voice/ics7750/tblshoot/tstcp.htm#xtocid16

MikeS
Find me at

http://www.packetattack.com

"The trouble with giving up civil rights is that you never get them back"

 

[Saeed42]

Make sure you don't have anything blocking port 67 & 68, I had a similar problem a while ago when I disabled bootp broadcasts (no ip bootp-server). You can debug all udp packets and see where it's failing.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Don't be content with being average. Average is a close to the bottom as it is to the top
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[dasmit]

Thanks for the posts, I figured out the problem. 2505 routers come with 8 hub ports on them, I was setting up the ip helper address in the S0 port, cause I could no set them up on the Hub port.

1 thing I did no know was if you configure e0 on the router it config's all the hub ports which is where I needed to setup the IP helper address, I kinda figured that out when I turn debug ip udp and I saw nuttin. =(

Thanks again
Dave

 

[spidermanfan]

You might want to check out MS technet article Q190930
"UDP Broadcast Forwarding by Cisco's IP Helper"

no ip forward-protocol udp netbios-ns
--Will stop NetBIOS Name Server

no ip forward-protocol udp netbios-dgm
--Will stop NetBios Datagram