isc dhcp server and client query

[Simon]

Asma Kouser <kousera at medha.com> wrote:

>      I am using ISC DHCP-4.3.6, and have a scenario in which the server is not allocating the IP address. I have updated the dhcpd.conf to give an IP address based on 'agent.circuit-id' and 'agent.remote-id' and there is only one IP in the pool to assign. When I connect a laptop the switch will add the agent info and forward it to the DHCP server and the DHCP server assigned the address which is defined in the Pool. now I have removed this laptop and connected another laptop on the same port, now the hardware address and the hostname will change but the agent information remains the same, in this case, the server is not allocating the IP address and says no free lease.

This is a known problem setting up such an arrangement. Even though you are using agent.<id> to allocate IPs to clients, the server internally still tracks leases again the Client-ID (or if that’s not present, it falls back to MAC address) - you’ll be able to see this int eh leases file.
So when you replace the client, as far as the server is concerned, it has no address it can give to the client - your config with agent.<id> will specify a specific IP address, but that address is still leased to the old client until it times out (or you manually release it - e.g. via OMAPI).


> Also, the ISC DHCP client does not send a DHCP Discovery or a request when the ethernet link is down and up again. Please let me know what modifications should I do to achieve this as well.

That will be down to the network management on your client. The client itself doesn’t manage interfaces - it relies on the OS’s network manager to start it and stop it as interfaces come up and down.

Simon