IP Helper

Unanswered Question
Mar 1st, 2010
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Hi all,


We have multiple VLAN's with one DHCP server.

I have configured what I think is correct to get different VLAN's picking up a dhcp address from the VLAN with the DHCP server in but, it doesn't seem to be working.

Here is the config. (VLAN 10 has the DHCP server with address 192.168.1.20)

VLAN 10

Ip address 192.168.1.1 /24

VLAN 20

ip address 192.168.10.1 /24

ip-helper address 192.168.1.20

I have set a laptop with DHCP TURBO giving out address 192.168.10.0 but the clients are not picking up any address.

Could you let me know if I am doing something fundamentally wrong please?

J.



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burleyman Mon, 03/01/2010 - 07:49
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The command for IP Helper is


ip helper-address 192.168.1.20



Mike

Sean Wright Mon, 03/01/2010 - 08:01
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I have actually typed it correctly on the router.


Jamie

burleyman Mon, 03/01/2010 - 08:19
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If that is the case everything you list looks ok. Can you post your DHCP configuration. Also your switch config.


Mike

chris.macleod Mon, 03/01/2010 - 08:13
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Hi Jamie,



Can you post the full config?

Is ip routing enabled?

If you manually specify the address can the client ping the dhcp server?



Thanks

Chris

Sean Wright Mon, 03/01/2010 - 08:32
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Hi Chris, thanks for your reply.


I can ping the DHCP server when I manually put in the IP address and routing is enabled.


Jamie

chris.macleod Mon, 03/01/2010 - 08:34
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Hi Jamie,


What is the result of:


show ip dhcp relay information trusted-sources



Thanks

Chris

chris.macleod Mon, 03/01/2010 - 08:49
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Hi Jamie,


Can you issue this command:


ip dhcp relay information trust-all


then run the previous show command.  Do you now get "All interfaces are trusted source of relay agent information option"

Sean Wright Mon, 03/01/2010 - 08:53
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Chris,


I haven't got that command?


If I type ip dhcp ? the options I have is snooping?


J

Sean Wright Mon, 03/01/2010 - 08:55
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Sorry long day, needed to be in conf t.


Ok so now when I run it I get "All interfaces are trusted source of relay agent information option".


J.

chris.macleod Mon, 03/01/2010 - 09:04
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Hi,


If you are still not get getting a DHCP lease can you post the switch config?  Is the DHCP server and client on the same switch?


Would also be a good idea to install wireshark on the DHCP server so you can see what if anything is being received from clients on VLAN20.  Might well be nothing to do with the switch config.



Thanks

Chris

Sean Wright Tue, 03/02/2010 - 07:51
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Hi Chris,


All sorted.


The DHCP server did not have a scope that was on the same subnet as itself.


As soon as I configured that it started giving out IP address.


Thanks for your help.


Jamie

chris.macleod Tue, 03/02/2010 - 07:54
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That's good thanks for updating the thread.


On 2 Mar 2010, at 15:52, "UWIC2"

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