Regarding DHCP on cisco router

Answered Question
Jul 23rd, 2009

Hi Friends,

I have configured two DHCP pools on a router say pool test (10.10.10.0/24) and pool best (20.20.20.0/24).

Now connected one L3 switch and created two vlan 10 and 20 with interface IP 10.10.10.1 and 20.20.20.1 resp. IP helper is given on both the interface with ip helper address 100.100.100.100/24 given on router fas 0/0 int.

one more vlan 100 is created on L3 with inteface IP 100.100.100.1/24.

router and switch are connected fas 0/0 and Gi 1/0/12 on switch with switch port s in vlan 100.

I am not getting ip address on any of the port which I assign to vlan 10 and 20.

Is this correct setup if not please tell how to configure vlan interface on L3 and dhcp scope on Router and how to connect router and switch.

Thanks,

Hemant

I have this problem too.
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Correct Answer by Peter Paluch about 7 years 4 months ago

Hello Hemant,

A few hints to consider:

1.) Can you ping the 100.100.100.100 from your L3 switch?

2.) Does your DHCP server (the router) have a route to reach your networks 10.10.10.0/24 and 20.20.20.0/24? It is required because when the DHCP Relay is used, the DHCP server responds to the DHCP Relay's address, in your case, 10.10.10.1 or 20.20.20.1.

3.) Try using the "debug ip dhcp server packet" on your DHCP server and see if the DHCP requests are being relayed to you and if there is a possible problem reported.

Best regards,

Peter

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Correct Answer
Peter Paluch Thu, 07/23/2009 - 02:26

Hello Hemant,

A few hints to consider:

1.) Can you ping the 100.100.100.100 from your L3 switch?

2.) Does your DHCP server (the router) have a route to reach your networks 10.10.10.0/24 and 20.20.20.0/24? It is required because when the DHCP Relay is used, the DHCP server responds to the DHCP Relay's address, in your case, 10.10.10.1 or 20.20.20.1.

3.) Try using the "debug ip dhcp server packet" on your DHCP server and see if the DHCP requests are being relayed to you and if there is a possible problem reported.

Best regards,

Peter

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