enable or disable IPv6 - Alibaba Cloud Linux - Alibaba Cloud Documentation Center

This topic shows you how to enable or disable IPv6 on an Elastic Compute Service (ECS) instance that runs Alibaba Cloud Linux 2.

Prerequisites

The instance type must support IPv6. For more information, see Overview of instance families.
The instance must be in an IPv6-enabled region and deployed in a Virtual Private Cloud (VPC) with an IPv6 CIDR block. For more information, see Create a VPC with an IPv6 CIDR block.

Background information

In Alinux images earlier than aliyun-2.1903-x64-20G-alibase-20190829.vhd, IPv6 is disabled by default. Starting from version aliyun_2_1903_x64_20G_alibase_20200221.vhd, IPv6 is enabled by default.

Enable IPv6

Temporarily enable IPv6

Important

This temporary configuration is lost when the instance stops or restarts. Use this method with caution.

In image versions aliyun_2_1903_64_20G_alibase_20190619.vhd and earlier, the .network files in the /etc/systemd/network/ directory are configured only with DHCP=ipv4. To temporarily enable IPv6, modify the file as follows:

Connect to the ECS instance.
For more information, see Connect to a Linux instance using Workbench.
Run the following command to go to the /etc/systemd/network/ directory:
```
cd /etc/systemd/network/
```
Run the ls command to find the .network file in the directory.
This topic uses the 50-dhcp.network file as an example.
Modify the 50-dhcp.network file.
```
vi /etc/systemd/network/50-dhcp.network
```
Press I to enter Insert mode.
Change the DHCP setting under [Network] to yes.
Note
The Name=eth* parameter matches all network interfaces, which means that all network interfaces will have their IP addresses and routes configured by using DHCP. To configure a specific network interface, change the Name parameter to that interface, for example, Name=eth0. For more information about .network files, see systemd.network.
```
[Match]
Name=eth*

[Network]
DHCP=yes
```
After making the changes, press Esc, enter :wq, and press Enter to save and exit.

Run the following commands to enable IPv6.

Enable IPv6 for all network interfaces.

sudo sysctl -w net.ipv6.conf.all.disable_ipv6=0
sudo sysctl -w net.ipv6.conf.default.disable_ipv6=0

Enable IPv6 for a specific network interface (for example, eth0).
```
sudo sysctl -w net.ipv6.conf.eth0.disable_ipv6=0
```

Permanently enable IPv6

To permanently enable IPv6, follow these steps: This configuration persists after the instance restarts.

Connect to the ECS instance.
For more information, see Connect to a Linux instance using Workbench.
Modify the /etc/sysctl.conf file.
```
vi /etc/sysctl.conf
```
Press i to enter Insert mode. Modify the file content by using one of the following methods:
- Delete the following configuration lines:
```
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
```
- Change the values in the configuration lines to the following:
```
net.ipv6.conf.all.disable_ipv6 = 0
net.ipv6.conf.default.disable_ipv6 = 0
net.ipv6.conf.lo.disable_ipv6 = 0
```
  To enable IPv6 for a specific network interface, use the following example configuration.
```
net.ipv6.conf.eth0.disable_ipv6 = 0
```
After making the changes, press Esc, enter :wq, and press Enter to save and exit.
Check for differences between the /etc/sysctl.conf file and the /etc/sysctl.conf file within initramfs.
```
diff -u /etc/sysctl.conf <(lsinitrd -f /etc/sysctl.conf)
```
Note
Alibaba Cloud Linux 2 uses an initial RAM filesystem (initramfs). If the /etc/sysctl.conf file within the initramfs differs from the main /etc/sysctl.conf file, the system might load the initramfs configuration at startup, overriding your changes.
If the two files are different, run the following command to regenerate the initramfs:
```
sudo dracut -v -f
```
Reboot the instance.
```
sudo reboot
```
Run the ifconfig command to verify that IPv6 is enabled.
If the output includes the following lines, IPv6 is enabled:
```
inet6 <Unicast address that starts with fe80::>
inet6 <IPv6 address of the instance>
```

Disable IPv6

Temporarily disable IPv6

Run the following commands to temporarily disable IPv6.

Important

This temporary configuration is lost when the instance stops or restarts. Use this method with caution.

Disable IPv6 for all network interfaces.

sudo sysctl -w net.ipv6.conf.all.disable_ipv6=1
sudo sysctl -w net.ipv6.conf.default.disable_ipv6=1

Disable IPv6 for a specific network interface (for example, eth0).
```
sudo sysctl -w net.ipv6.conf.eth0.disable_ipv6=1
```

Permanently disable IPv6

The following steps permanently disable IPv6. The configuration persists after the instance restarts. You can disable IPv6 by using either of the following methods.

Permanently disable IPv6 by using one of the following kernel parameters.
- ```
sudo grubby --args="ipv6.disable_ipv6=1" --update-kernel=/boot/vmlinuz-$(uname -r)
```
- ```
sudo grubby --args="ipv6.disable=1" --update-kernel=/boot/vmlinuz-$(uname -r)
```
Note
The --args="ipv6.disable_ipv6=1" parameter disables IPv6 for network interfaces, while --args="ipv6.disable=1" disables the entire IPv6 kernel module. For more information, visit Linux kernel IPv6.
Modify the /etc/sysctl.conf file to permanently disable IPv6.
1. Modify the /etc/sysctl.conf file.
```
vi /etc/sysctl.conf
```
2. Press I to enter Insert mode and change the configuration to the following:
```
net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.default.disable_ipv6=1
```
  Disable IPv6 for a specific network interface. Example:
```
net.ipv6.conf.eth0.disable_ipv6=1
```
3. Reboot the instance.
```
sudo reboot
```
4. Run the ifconfig command to verify that IPv6 is disabled.
  If the output does not include the following lines, IPv6 is disabled:
```
inet6 <Unicast address that starts with fe80::>
inet6 <IPv6 address of the instance>
```

Configure IPv6 for multiple network interfaces

To configure multiple IPv6 addresses, follow these steps.

Connect to the ECS instance.
For more information, see Connect to a Linux instance using Workbench.
Run the following command to go to the /etc/systemd/network/ directory:
```
cd /etc/systemd/network/
```
Run the ls command to find the .network file in the directory.
In this example, the 10-eth0.network file is used.
Run the cp command to copy it to a new configuration file.
For example:
```
cp 10-eth0.network 20-dhcp.network
```

Run the following command to modify the new configuration file.

sed -i 's/^Name.*$/Name=*/g' /etc/systemd/network/20-dhcp.network

Restart the systemd-networkd service to apply the changes.
```
sudo systemctl restart systemd-networkd
```