Binding between a switch interface and DHCP

danny4569 · ‎11-09-2011

Hi all.

I am looking for a way to bind between a switch interface (cat 3750X) and a DHCP server reply.

The switch can operate as the DHCP server .

For example,

a PC connected to interface Gi 1/0/1 will lways get IP address 10.0.0.1 because it is connected to interface Gi 1/0/1, a PC connected to interface Gi 1/0/5 will lways get IP address 10.0.0.5 because it is connected to interface Gi 1/0/5 and so on... (no matter the source MAC address who sends the DHCP request).

Is it possible on CAT 3750X?

Danny.

Krishnendu AR · ‎11-15-2011

Guys,

Even Im keen to know if this is possible.

Krishna

CSCO11508096 · ‎11-15-2011

Hi,

DHCP protocol recognizes DHCP clients by the client identifier option in the DHCP packet. Clients that do not include the client identifier option are identified by the client hardware address. When you configure this feature, the switch port, becomes the client identifier. and you can bind the port with the specific IP Address.

enable this feature using command in global config mode:

ip dhcp use subscriber-id client-id

ip dhcp subscriber-id interface-name

address 10.0.0.1 client-id "Gi 1/0/0" ascii

danny4569 · ‎11-16-2011

Hi.

I vave the following configuration on my 3750 switch:

ip dhcp use subscriber-id client-id

ip dhcp subscriber-id interface-name

IP dhcp pool VLAN2

network 25.0.0.0 255.255.255.0

address 25.0.0.1 client-id "Fa 1/0/0" ascii
address 25.0.0.2 client-id "Fa 1/0/1" ascii
 
interface FastEthernet 1/0/1
switchport access vlan 2
switchport mode access
ip dhcp server use subscriber-id client-id
spanning-tree portfast
 
The problem is that the DHCP server (which is the CAT3750) assigne any 
IP address from the pool but not the specific address configured.
For example: at this moment interface Fa 1/0/1 gets 25.0.0.7
Any idea why?

pascal · ‎11-16-2011

What does "sho ip dhcp bind" show for the client-id?

danny4569 · ‎11-17-2011

Hi Pascal.

The output of the command: "show ip dhcp binding"

IP address client ID/H/W address/User name Lease expiration Type

25.0.0.1 4661.2031.2f30.2f30 infinite manual

25.0.0.2 4661.2031.2f30.2f31 infinite manual

25.0.0.3 4661.2031.2f30.2f32 infinite manual

25.0.0.7 4661.312f.302f.31 Mar 02 1993 06:26 PM Automatic

The PC gets 25.0.0.7 when it is connected to interface Fa 1/0/1

danny4569 · ‎11-17-2011

Problem was solved!

The problem was with the ascii name and the way you type the name of the interface were you want to get a manual/static IP address acording to the interface name.

when configuring the command: address 25.0.0.5 client-id "name of the interface" ascii

you should write the short name of the interface exactly as it is being showed under the command "show interface status" for example.

in my my case: address 25.0.0.5 client-id "Fa1/0/5" ascii with NO space btween Fa and number.

Danny.

Phuong Trinh · ‎09-28-2012

Dany, I had the same problem and just did what you were showing but still not working. Are you using the external DHCP server or from IOS?

Thanks

Phuong

danny4569 · ‎10-02-2012

Hi Phuong.
I am using the 3750/3750X IOS as my DHCP server.

Don't forget to confgure also each interface on the switch with the command:

ip dhcp server use subscriber-id client-id.

Best regards,

Danny.