MAC address DHCP reservation configuration on ISR 921-4P router

[ben.r.fr]

Hi,
I need to make mac address reservation by dhcp on my C921-4P router but when I do dhcp pool configuration the target device address is not given as I configure it.

I tested deleting the pool and recreating another one by integrating the "client-identifier" instead of the "hardware-address" but I had the same result.

After that I tested another time but the router tells me "A link in this subnet already exists."

Is anyone can help me to remove the binding and config the mac address reservation correctly ?

In advance thank you for your help and answers

Benjamin

[balaji.bandi]

as long as the MAC address of the device correct the device get reserved IP address - make sure check the MAC address.

Try :

ip dhcp pool vs_1
host 192.168.X.X 255.255.255.0
client-identifier 0100.XXXX.XXXX.XX

client-identifier option prepends a 01 (for Ethernet) to the MAC address.

[Georg Pauwen]

Hello,

try and disable the DHCP service first:

no service dhcp

[ben.r.fr]

Hello, thank you for your responses and guidance.

@Georg Pauwen, I have a production network and a DHCP service that distributes a number of IPs.
In absolute, I would like to not have to stop the service, do I have another solution or stopping the DHCP service will have no consequence if I restart it after my test?
I also assume that if I stop the DHCP service, I lose my remote access.

@balaji.bandi, yes I tested the MAC address, the device is an old Macbook (still alive to test now). I tested the DHCP MAC config with the two MAC addresses still available for him, for ETH and for WIFI.

- I can do the test again with another old Windows device, do you think it will show if the MAC address of the Macbook is correct ? 
- What about the "binding error" do you think?

thanks a lot for your help

[Georg Pauwen]

Hello,

stopping and restarting the DHCP service will not affect existing client leases, however, in a production environment, you might want to schedule this during off hours anyway.

That said, I am not sure if you have mentioned if you have tried to clear the binding ?

clear ip dhcp binding ip_address

[ben.r.fr]

Hello,
ok thank you for your answer, yes the operation will be carried out during off-peak periods and I will carry it out on site to secure the process.
I will try "clear binding" for the ip and stop and restart the service.
I will also try with another device and let you know.

Sorry for this question (i'm junior technician), but to restart the DHCP service, the command would be fine : service dhcp?

Thanks a lot for your answers
Benjamin

[Georg Pauwen]

Hello,

exactly:

ISR921#conf t

ISR921(config)#no service dhcp <-- stops the DHCP service

ISR921(config)#service dhcp <-- starts the DHCP service

[ben.r.fr]

Thank you very much, I will keep you informed of the progress to validate the discussion