Linux renew dhcp lease

How to Renew my DHCP Lease on Ubuntu?

DHCP can be used to automatically get an IP address and other network configurations from a DHCP server. However, sometimes the DHCP lease may expire, and a user needs to renew it to continue using the internet. The device will automatically request a new lease when a lease expires, but sometimes this process can fail.

This article will discuss the manual process to renew the DHCP lease on Ubuntu using the content below.

Understanding DHCP Lease

Before we jump into the steps for renewing your DHCP lease on Ubuntu, it’s important to understand what a DHCP lease is and how it works. A DHCP lease is a contract between a device and a DHCP server that specifies an IP address, subnet mask, gateway, and DNS server(s) for the device. This process ensures that IP addresses are efficiently utilized and prevents conflicts between devices that may request the same IP address.

Renew DHCP Lease on Ubuntu

Renewing the DHCP lease on Ubuntu consists of multiple steps, which are discussed below:

Step 1: Check the Current IP Address

Before renewing your DHCP lease, it’s essential to check your current IP address to ensure that you have lost network connectivity using the below command.

The current IP address for the system is 192.168.126.138.

Step 2: Release Current DHCP Lease

To release the current DHCP lease, a user needs to write the below command in the terminal:

Here is the breakdown of the command:

dhclient: The “dhclient” command is a client program for the DHCP protocol that communicates with the DHCP server to obtain an IP address lease and other network configuration settings.

-r: The “-r” option instructs the dhclient to release the current DHCP lease. This means that your device will notify the DHCP server that it no longer needs the current IP address and configuration parameters assigned to it, and it can be given to another device.

In the output, “killed old client process” means that the dhclient command has terminated an old instance of itself. This happens when a previous dhclient process was running in the background and was not properly terminated, which can cause conflicts when trying to obtain a new DHCP lease.

A user can also use the “-v” option along with this command which instructs the dhclient command to run in verbose mode. This option will provide detailed information about the DHCP process, including messages and error codes.

Step 3: Renew the DHCP Lease

After releasing the current DHCP lease, a user can renew a new DHCP by typing the below command:

This command will request a DHCP server to assign a new IP address to your device. The DHCP server will respond with an available IP address and automatically assign the new IP address to your device:

It can be seen in the above image that a new IP address has been assigned, which is 19.168.126.140, and the previous IP address was 192.168.126.138. The same thing could be done by using the “-v” option to provide additional information:

Note: Releasing and Renewing the DHCP Lease can also be done by providing the name of the network, which is “ens33” in this case:

$ sudo dhclient -r ens33 $ sudo dhclient ens33

Executing these two commands will release and renew the DHCP lease for the interface ens33 and provide you the new IP address:

Conclusion

Renewing the DHCP lease is a simple process that can resolve many connectivity issues on Ubuntu. There are two major steps involved in renewing the DHCP lease, which is to release and renew the current DHCP lease, which has been discussed in detail in this article.

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How to Release old IP or force Renew DHCP lease IP in Linux

In this article, we will see how to release old IP or force renew DHCP lease IP in Linux. Dynamically allocated IP is an IP leased out from a DHCP server for a particular amount of time over a network. If you are using a lease IP then you always have to renew your ip before the lease period expires. Usually, when a lease reaches 50% of its validity time period, the DHCP client unicasts a DHCP Request message to the DHCP server to request lease renewal. The same can be forced manually through a dhcp client tool in Linux Systems.

What is DHCP

The Dynamic Host Configuration Protocol is a network management protocol used on Internet Protocol networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a client–server architecture.

How to Release old IP or force Renew DHCP Lease IP in Linux

If you have any DHCP lease IP allocated to an interface which you want to release due to certain reasons then you always have the option to release it by using DHCP client tool called dhclient. For example, in my case I have two interfaces attached to my system — enp0s3 and enp0s8 .

To release the IP attached to both the above interfaces, we need to use sudo dhclient -r -v command. But sometimes what happens is that the IP does not get released as you can see below.

Please don’t ever try to release the IP over SSH connection as it will disconnect you from the host system and you may not be able to reconnect unless a new IP is assigned which is known to you.

If we try to check again the IP got released or not using ip addr sh command then we can notice that nothing happened. The assigned IP did not got released.

If you try to release IP from specific interface by choosing the interface using sudo dhclient -r -v enp0s3 command then also you can notice that the IP did not got released. This is a very common scenario faced by lot of folks hence I purposefully chosen this one while trying to explain how to release the DHCP lease IP so that you will understand what needs to be done here.

Sometimes even if you try to kill the dhclient process using kill -9 command then you will notice that it is getting started every time you kill this process and the IP is not getting changed. To check the process ID of currently running dhclient program, you can use ps -ef | grep dhclient command as shown below.

In my case process ID(PID) is 2167 , so to kill this one we are using kill -9 2167 command as shown below.

Now if I try to check the process again, I can see that a new dhclient command is launched with process ID(PID) 2169 . So now you must be wondering how did this happen.

Well, this happened because the network interfaces are currently controlled by Network Manager. You can verify this on Debian/Ubuntu systems by checking one of the below netplan configuration file depending on Ubuntu installation you are currently having.

Please note if you are using RHEL/CentOS based systems, then you need to check /etc/sysconfig/network-scripts/ifcfg- configuration file.

You can check the running status of Network Manager by using sudo systemctl status NetworkManager command as shown below.

If you are also facing problems like above, then you can try below solutions that works for you.

Solution 1: Restart Network Manager

First solution you can try is that you can restart Network Manager by running sudo systemctl restart NetworkManager command as shown below.

Solution 2: Using nmcli command

If the first solution does not work then next you can try restarting your connection using nmcli command. Here you need to first check the current connection using nmcli con command as shown below.

Then first take down the connection for the interface where you need to renew the IP. In our case, let’s say we want to renew the IP of enp0s3 interface, then we need to run nmcli con down id «Wired Connection 1» command after releasing the IP as shown below.

Then bring up the connection using nmcli con up id «Wired connection 1» command as shown below.

Solution 3: Restart systemd-networkd

If second solution also did not worked out, then you can try restarting systemd-networkd once by using sudo systemctl restart systemd-networkd command as shown below.

After applying above solution, you can see that you will be able to release the IP as shown below.

You can verify the same by checking the status of ip assigned to network interfaces using ip addr sh command as shown below. From the output, you can see that none of the IP is assigned to both the interfaces — enp0s3 and enp0s8 . This confirms that IP release was successful.

Once the IP is released, you will be able to get the new ip by running sudo dhclient -v command as shown below.

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Renew DHCP lease in systemd-networkd

How do I tell systemd-networkd to renew my DHCP lease? I know with dhclient it’s as simple as dhclient -r eth0 && dhclient eth0 , as explained in many other answers on this site, but how do I do it for systemd-networkd ? I’m in Ubuntu 18.04 Server.

3 Answers 3

Starting from systemd version 244, you can renew DHCP lease in systemd-networkd with the following command:

Ubuntu 20.04 shipped with systemd 245.4 and is the first version of Ubuntu where this command is available.

Nice find! I’m trying to find out which version of Ubuntu that systemd 244 is first included in, so we can add that to your answer. Unfortunately, the release notes don’t seem to specify.

You can find this information well and conveniently formatted here. Ubuntu 20.04 is the oldest release with systemd >244.

I found a freedesktop.org mailing list post from Tom Gundersen in August 2014 that answers my question, at least as of the time it was written:

> Is there a way to force a DHCPv4 release/renew with systemd-networkd?

We don’t currently allow dynamic interaction with networkd, but you can force renew the release by either restarting networkd or unplugging/replugging the cable (or switching your wifi off/on if that’s what you are using).

-t

So apparently if you do one of these two things, systemd-networkd will renew your DHCP lease.

Did it work for you? This seems right, but systemctl restart systemd-networkd didn’t help, only dhclient -v -r eth0; dhclient -v eth0 (testing with dhcpdump -i eth0 on other terminal).

@PabloA If you’re using systemd-networkd , then you don’t want to use dhclient . it will interfere with systemd-networkd . Or, perhaps more accurately, systemd-networkd will probably interfere with your use of dhclient at some point. I’m not 100% sure that it worked, as I didn’t really look that closely in my router’s webpage after running the command, but I assume it did since I see that in multiple other answers on this site that that’s the correct way to do it for systemd-networkd .

I have found that if you do a restart on systemd-networkd , it ignores the previous lease and just starts over with a clean request.

If you’re also using a dhcpd that does a ping check you end up with a second. That might be an interaction with how I’ve set up the network config. We use Critical because otherwise systemd-network sends a DHCPRELEASE on shutdown and, most critically, also forgets the lease it had before. So rebooting two systemd-networkd servers at the same time has a very high chance of both of them losing their IP addresses.

I’m unsure what the conditions that cause this to happen are, however, I’ve found that if you send a -HUP to systemd-networkd , and then start the service (not restart) it will use the leases that are in /var/run/systemd/netif as you would expect.

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