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Beginner

IP Helper

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.

13 REPLIES 13
Collaborator

Re: IP Helper

The command for IP Helper is

ip helper-address 192.168.1.20

Mike

Beginner

Re: IP Helper

I have actually typed it correctly on the router.

Jamie

Collaborator

Re: IP Helper

If that is the case everything you list looks ok. Can you post your DHCP configuration. Also your switch config.

Mike

Beginner

Re: IP Helper

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

Beginner

Re: IP Helper

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

Beginner

Re: IP Helper

Hi Jamie,

What is the result of:

show ip dhcp relay information trusted-sources

Thanks

Chris

Beginner

Re: IP Helper

Hi Chris,

Nothing appears when I runn that command?

J.

Beginner

Re: IP Helper

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"

Beginner

Re: IP Helper

Chris,

I haven't got that command?

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

J

Beginner

Re: IP Helper

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.

Highlighted
Beginner

Re: IP Helper

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

Beginner

Re: IP Helper

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

Beginner

Re: IP Helper

That's good thanks for updating the thread.

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

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