Renew dhcp lease linux

How to renew or release a dynamic IP address in Linux

The DHCP client in Linux is called dhclient. It requests dynamic IP addresses from the DHCP server, which «leases» addresses to clients for a set amount of time. dhclient can be invoked manually to «release» the client’s currently assigned IP address, and get another address from the DHCP server.

Normally, dhclient produces no output, to see what it’s doing, we need to give it the -v (verbose) option. We need to run dhclient as root with the sudo command, because changing the system networking configuration requires escalated privileges.

Let’s start by running dhclient verbosely, without any other options. It should reach out and say «hello» to our DHCP server, which, in our example is home router.

The above output tells us that dhclient requested an address from the DHCP server (DHCPREQUEST). It sent this request from our wireless Internet interface (wlan0). The DHCP server responded with a simple acknowledgement of our request (DHCPACK). That’s because we already had an IP address assigned to us, so the DHCP server didn’t have anything to do. Note that the DHCP server also told us how long our dynamic IP address will last: 42516 seconds (about 12 hours from now, at which point it will be renewed automatically).

So let’s manually release our address with -r. Let’s keep the -v option in there so we can see what’s going on:

In the above example, the command tells the DHCP server to release the IP address.

On some variants of Linux or Unix, releasing your IP address this way may also inherently bring down your network interface. In this case, use your network manager to re-connect to your network. This process varies from OS to OS; if you’re not sure how to connect to your network, consult the documentation of your specific OS. If you’re using the X Window System, you can usually reconnect by clicking the network icon in your system tray, and selecting the Connect option.

Источник

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

Table of Contents

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.

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.

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.

• 01-netcfg.yaml
• 01-network-manager-all.yaml
• 50-cloud-init.yaml

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.

Источник

How to Renew DHCP IP on Debian 11

What Is DHCP?

The DHCP or Dynamic Host Configuration Protocol is used to assign devices random IP addresses automatically. When using a server or router with a DHCP server, clients don’t have to set their IP addresses manually. They need to request it from the DHCP. The IP addresses provided by DHCP are known as Dynamic IP addresses, while IP addresses set manually are known as Static IP addresses.

Renew the IP Address on Debian 11 Using DHCP (All Network Cards):

The dhclient tool is the main Linux method to deal with DHCP or dynamic IP addresses. When our system boots, dhclient tries to configure a dynamic IP address for each network device in our system. However, dhclient can be invoked by the user at any time to renew an interface IP address.

In the first example of this tutorial, we will execute dhclient followed by the -r flag to release the current IP address. It is important to note that the dhclient command will release all IP addresses when a network device isn’t specified.

Note: After running this command, you’ll lose your network connection. You will recover it by following the next steps of this tutorial:

Now, your system released its IP address, and your internet connection is gone.

You also can implement the -v (verbosity) option to get the whole releasing IP process detailed in the output as shown in the example below:

Once your IP address is released, you can request a new one using the dhclient command without additional parameters, as shown in the screenshot below:

And you also can implement the -v flag to get a detailed output, as shown in the following example:

As you can see, the IP address 192.168.1.103 was assigned to the wlp3s0 device.

Renew the IP Address on Debian 11 Using DHCP (Specific Network Card):

As mentioned previously, if you don’t specify a device when running the dhclient command, all network card IP addresses will be affected.

Specifying a network card when running dhclient is pretty simple. Just add the network card name at the end of the command.

The following example shows how to release the IP address of the wlp3s0 Wi-Fi card specifically. As mentioned in the first steps of this tutorial, the -v option was added just to get a detailed output. You can skip it.

Then, to get a new dynamic IP address for the wlp3s0 Wi-Fi card specifically, run the following command:

As you can see, the IP address was properly assigned to the wlp3s0 network device.

How Does DHCP Work?

When you run the dhclient command, or when you boot your computer, dhclient sends broadcast messages (DHCP Discover) to the subnets in order to discover available DHCP servers. The DHCP Discover packet includes the physical computer MAC address for the client to be identified by the server. Then, the DHCP server sends a response (DHCP OFFER) offering to send an IP address. The client replies back with a request packet or DHCP Request accepting the offer. Then, the DHCP server assigns an IP address to the client, integrating it to the network. This process is known as DHCP negotiation.

In terms of packets, we can summarize this process as DHCPDISCOVER>DHCPOFFER>DHCPREQUEST>DHCPACK where:

DHCPDISCOVER: A packet is sent from the client to subnets looking for available DHCP servers to obtain the IP address.

DHCPOFFER: When the packet is received by a DHCP server, the server sends a DHCPOFFER message back to the client as identified by its MAC address, then offering to assign it a free or unused IP address.

DHCPREQUEST: The client sends a packet to the DHCP server accepting the offer. If more than one DHCP server offered the IP address, the client would accept the first received, and other DHCP servers would be notified the initial request was already satisfied.

DHCPACK: Finally, after the DHCP server got the final request packet from the client. It will reply with a DHCPACK packet completing the IP assignment.

How to Check the DHCP Lease History?

In some cases you may want to see your dynamic IP addresses history. This can be achieved by checking the system logs located at /var/log/syslog. The following command allows you to see all negotiation processes which involve the dhclient command:

As you can see, we can see the whole negotiation process and previously assigned IP addresses.

Note: If this article was interesting for you, you may want to read Advanced Linux Network Commands.

Conclusion:

As you can see, renewing an IP address on Debian 11 using DHCP is pretty easy. Understanding how DHCP servers and clients work is a basic knowledge any Linux user must learn to understand how many devices acquire their IP address. While dynamic IP addresses do not make sense in planned networks, they are a great way to manage public IP addresses since two devices can’t have the same address. As you can see, requesting a dynamic IP address from a Linux device can be done by any Linux user level if there is privileged access. In many cases, when you connect to a public network but don’t receive internet access, you may want to try to request a dynamic IP address using the method explained. This was helpful for me in some situations.

For additional information on the dhclient command, you can visit the man page at https://linux.die.net/man/8/dhclient.

Thank you for reading this tutorial explaining how to renew DHCP IP addresses on Debian 11. Keep following Linux Hint for additional Linux tips and tutorials.

About the author

David Adams

David Adams is a System Admin and writer that is focused on open source technologies, security software, and computer systems.

Источник