Login details hacked.

Quick question regarding IP lease time with DHCP. Does the IP address automatically renew if those connected devices are still responding to server at lease expiry?

The lease renewal process is a bit more complex than we tend to think of it as it is made up of two components and a fair few data packet exchanges.

The first time the device asks the server, ( router), for an IP there is communication between the device and the server and the lease is set and the ip issued

The device attempts renewal at 50% of the lease time It is usually renewed at this point. If the lease time expires then the server cancels the lease and the device must re-apply ( 50% is the default Renewal time but can be changed in some systems to suit system needs)

What this means in reality is the lease will be renewed and thus remain active for as long as the device is on and so requires it, but when the device is off the lease expires and is available for use by other devices .

If you want all the gory details you could take a look here ...

How the DHCP Lease Renewal Process Works - Network Services Windows Server 2003

DHCP lease does seem quite complicated. I'm actually struggling to understand it's purpose. It seems more useful when there are many devices on a network that could come and go quickly. Will give the link you posted a go.

So the only real way the lease can expire is when the server loses contact with the device? Would this mean a complete shutdown of the PC/device? For example shutting down my PC down and removing the power cable. Will that trigger a new IP lease? Or restarting the smartphone?

DHCP was not designed for use with a single router based small Peer to Peer network of a few devices, but for the large server - client networks wit hundreds of thousands of devices - indeed it is used my ISPs to allocate the many External WAN IP addresses, of their clients.

back in the home network

If you set your lease time to 60 minutes then the devices will renew every 30 minutes, (half the lease time), but should the device be switched off for more than an hour (the lease time), the server, ( the router ), will revoke the lease, and return the IP to the pool of available addresses, and the device will need to negotiate again the next time it connects, this means that you will always have the highest number of available IP addresses free. the disadvantage is that you cannot be sure that the device will have a certain IP address at any time.

In the real world where most systems, in a home environment run for a maximum of 12 hours and a shut down for 12 hours overnight, If you set the lease for 24 hours, ( or better still 26 Hours ), your devices will retain the same IP address for long periods and only change if they are off for a while for repair or maintenance.

There are "tricks" built into the dhcp server that can force the same IP address to be allocated to a certain machine - this uses the Unique MAC (machine access code), this is unique to every network device in the world, [ A large Hexadecimal number), this is useful if you wish to talk to other machines on the network easily, such as knowing that a network printer will always be at an address means you can print to it from more devices, not just Windows machines but Android, Linux, and others.