IP Helper - Isnt working

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Jun 18th, 2010
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Hi all,

Hope you can help. I thought IP helper was just a matter of putting the cmd on an interface that is a different subnet from the subnet of the DHCP server and hey presto, DHCP across broadcasts domains. Doesn't seem to be working for me?


Here is my config:-


interface Vlan800
description CSM-staff-gnd
ip address 192.168.162.2 255.255.255.0 secondary
ip address 192.168.161.2 255.255.255.0
ip helper-address 192.168.176.30
no ip redirects
ip pim sparse-mode
bridge-group 1


interface Vlan803
description CSM-backline
ip address 192.168.176.2 255.255.255.0


So the DHCP server is in Vlan 803 ip address is 192.168.176.30. If I connect a pc directly into vlan 803 it gets an IP. If I connect a pc in Vlan 800 I get nothing.


Any ideas?


J.

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John Blakley Fri, 06/18/2010 - 07:03
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Why are you using a bridge group under the vlan that has your helper? You may try taking that off, but I'm not sure what impact it'll have on your production environment.


HTH,

John

spremkumar Fri, 06/18/2010 - 07:04
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Hi


Have you enabled ip routing so that the intervlan communication can happen.


regds

Richard Burts Fri, 06/18/2010 - 14:35
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J


There are several things that can prevent ip helper-address from working. In my experience one of the most common problems is that the server address is not reachable from the subnet where the helper address is configured. A good test is whether a PC in the subnet of VLAN 800 (assigned an address in that subnet and with the router interface address as its default gateway) can ping the address specified by the helper address. Since the DHCP server appears to be in the subnet of a connected interface, I suspect that this is not the problem in your case, but it might be a good idea to test it,


The other common problem with helper address is that the DHCP server does have a correct scope for its local subnet (VLAN 803) but does not have a correct scope for the remote subnet (VLAN 800). Can you verify whether the DHCP server has a correct scope configured for 192.168.161.0?


HTH


Rick

Jamie Hancock Mon, 06/21/2010 - 04:10
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As is normall for me, as soo as I post a problem I figure out the problem!


I didn't have the scope setup on the the dhcp server to correspond to the request from the vlan.


Thanks for your help guys.


J.

Richard Burts Mon, 06/21/2010 - 04:39
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J


I am glad that you figured out the problem and now have it resolved. Thanks for posting back to the forum indicating that you have resolved the problem and what you did to solve it. It makes the forum more useful when people can read about a problem and can read what successfully resolved the problem.


HTH


Rick

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