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To disable IPv6 on Ubuntu, first choose the scope you actually need. Use sysctl for an immediate, host-wide change without rebooting; save those settings in /etc/sysctl.conf or /etc/sysctl.d/ to make them persistent. Add ipv6.disable=1 to GRUB when IPv6 must be disabled during every boot. If only one NetworkManager profile should avoid IPv6, set that profile’s ipv6.method to disabled.
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These methods are not interchangeable. A GRUB parameter affects the whole kernel and requires a reboot, while a NetworkManager setting affects one connection profile. Netplan behaves differently depending on whether it renders configuration for networkd or NetworkManager, and turning off DHCPv6 alone does not turn off every IPv6 function.
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Choose the right IPv6-disable method
Ubuntu installations commonly combine a kernel networking stack with either NetworkManager or Netplan-rendered networkd. Decide whether you need a test, a persistent host policy, a boot-time kernel disable, or a single-profile change before editing anything.
| Method | Scope | When it takes effect | Survives reboot? | Best use | Rollback |
|---|---|---|---|---|---|
Runtime sysctl |
Host-wide running system | Immediately | No | Testing or a temporary diagnostic | Set the same flags to 0 |
Persistent sysctl |
Host-wide | After reload, and on future boots | Yes | A persistent policy while retaining normal boot | Remove the entries or change them to 0, then reload |
GRUB ipv6.disable=1 |
Entire kernel | At boot | Yes | A broad disable before network services start | Remove the parameter, run update-grub, reboot |
| NetworkManager profile | One saved connection | When the profile is reactivated | Yes for that profile | A wired, Wi-Fi, VPN, or other profile that must not use IPv6 | Set ipv6.method back to auto or the required method |
| Netplan options | Interfaces described by a Netplan file | When Netplan is applied | Yes while the file remains authoritative | Controlling DHCPv6 and link-local behavior | Restore the previous YAML and apply it |
The Ubuntu Community Hub procedure documented for Ubuntu 22.04 and 24.04 uses the three sysctl flags shown below. Canonical’s Netplan documentation identifies networkd as Ubuntu Core’s default renderer, while Netplan can also render through NetworkManager. Confirm the Ubuntu release and renderer on the machine before choosing a persistent recipe.
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Disable IPv6 immediately with sysctl
A runtime sysctl change affects the running kernel and does not require a reboot. It is the quickest way to determine whether IPv6 is related to a connectivity or application problem. It is host-wide, so every interface and service using the kernel networking stack is affected.
Apply the temporary setting
- Open a terminal or an administrative shell.
- Run all three settings, including the loopback setting:
sudo sysctl --write net.ipv6.conf.all.disable_ipv6=1
sudo sysctl --write net.ipv6.conf.default.disable_ipv6=1
sudo sysctl --write net.ipv6.conf.lo.disable_ipv6=1all changes the system-wide setting, default supplies the setting used for interfaces created later, and lo covers the loopback interface. Running only one line can leave another path able to expose IPv6 configuration.
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List addresses and look for remaining IPv6 entries:
ip aInspect the kernel value directly when you need an unambiguous check:
cat /proc/sys/net/ipv6/conf/all/disable_ipv6
cat /proc/sys/net/ipv6/conf/default/disable_ipv6
cat /proc/sys/net/ipv6/conf/lo/disable_ipv6A value of 1 indicates that the corresponding disable flag is set. The ip a output is useful for confirming what each interface currently advertises; the /proc/sys files confirm the kernel settings themselves.
Undo a temporary change
Set each flag back to 0:
sudo sysctl --write net.ipv6.conf.all.disable_ipv6=0
sudo sysctl --write net.ipv6.conf.default.disable_ipv6=0
sudo sysctl --write net.ipv6.conf.lo.disable_ipv6=0Check ip a again after restoring the values. Interfaces or services that were disconnected while testing may need to reconnect through their normal network manager.
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Make the sysctl disable persistent
A runtime value is not a configuration policy: it can disappear at the next boot. To keep the host-wide setting, place the same three flags in /etc/sysctl.conf or in a dedicated file under /etc/sysctl.d/.
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Option A: edit /etc/sysctl.conf
- Open the file with administrative privileges, for example:
sudo editor /etc/sysctl.conf- Add these lines once, without changing their names:
net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.default.disable_ipv6=1
net.ipv6.conf.lo.disable_ipv6=1- Save the file and reload it:
sudo sysctl -pThe reload applies the values to the current session; the file supplies them again on subsequent boots.
Option B: use a dedicated drop-in file
A file in /etc/sysctl.d/ keeps the local policy separate from the main configuration. Create a clearly named file such as /etc/sysctl.d/99-disable-ipv6.conf, add the same three lines, and load the sysctl configuration with the system’s applicable reload command:
sudo editor /etc/sysctl.d/99-disable-ipv6.conf
sudo sysctl --systemAfter either option, verify both the values under /proc/sys/net/ipv6/conf/ and the addresses shown by ip a. If another configuration file defines the same key later in the load order, the later value can win; search the sysctl configuration files when the result does not match the line you added.
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Delete the three entries, or change their values to 0, in whichever file you used. Reload with sudo sysctl -p for /etc/sysctl.conf or the applicable system-wide reload command for a drop-in. Confirm that the values are 0 and that normal IPv6 addresses return when the interface reconnects.
Disable IPv6 at boot with GRUB
The kernel parameter ipv6.disable=1 is a broad boot-time switch. It prevents IPv6 from being enabled by the kernel for that boot, rather than waiting for userspace network configuration. It is appropriate when every interface and service must start with IPv6 disabled, but it requires editing the boot configuration and rebooting.
Add the kernel parameter
- Open the GRUB defaults file:
sudo editor /etc/default/grub- Find
GRUB_CMDLINE_LINUX_DEFAULTand appendipv6.disable=1inside its existing quotation marks. For example, preserve existing options and add the new one:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash ipv6.disable=1"Do not remove options you still need. If the file has a different existing command-line value, append the parameter to that value instead of replacing it.
- Regenerate the boot menu:
sudo update-grub- Reboot to load the new kernel command line:
sudo rebootSchedule this change for a maintenance window when working over SSH or on a remote machine: the reboot interrupts the session, and an incorrect GRUB edit can affect boot.
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Verify the boot-time setting
After the machine returns, run ip a and inspect the sysctl values under /proc/sys/net/ipv6/conf/. The verification must happen after the reboot; changing /etc/default/grub alone does not alter the currently running kernel.
Undo the GRUB disable
- Open
/etc/default/gruband remove onlyipv6.disable=1. - Run
sudo update-grubagain. - Reboot.
Once the system is back up, verify the interfaces and applications that require IPv6.
Disable IPv6 for one NetworkManager connection
NetworkManager’s ipv6.method property includes auto, dhcp, manual, disabled, ignore, and shared. Setting it to disabled changes one saved connection profile, not the entire host. Other profiles can continue using IPv6.
Find the exact profile name
List saved profiles:
nmcli connection showUse the profile name from the NAME column. Names can contain spaces, so quote the name in subsequent commands.
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- Modify the profile:
sudo nmcli connection modify "PROFILE NAME" ipv6.method disabled- Reactivate it so the new setting is used:
sudo nmcli connection down "PROFILE NAME"
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Verify the profile setting
Display the profile’s IPv6 method:
nmcli connection show "PROFILE NAME" ipv6.methodThen inspect the active addresses with ip a. The profile setting persists in NetworkManager’s connection data, so it is reapplied whenever that profile is activated. It does not alter a different Wi-Fi network, wired profile, VPN profile, or interface that has its own connection definition.
Restore IPv6 for the profile
Set the method back to the mode the connection requires, commonly automatic configuration:
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sudo nmcli connection modify "PROFILE NAME" ipv6.method auto
sudo nmcli connection down "PROFILE NAME"
sudo nmcli connection up "PROFILE NAME"If the profile previously used manual, dhcp, shared, or another method, restore that original value rather than assuming auto is correct.
What Netplan can and cannot disable
Netplan is a configuration layer, not a single networking daemon. Its renderer determines whether generated configuration is handed to networkd or NetworkManager. Canonical documentation states: “Ubuntu Core’s default Netplan configuration defers networking to networkd.” Other Ubuntu installations can explicitly use NetworkManager.
Identify the renderer and the authoritative file
Inspect the YAML files under /etc/netplan/ and look for a top-level renderer: value. A value of networkd means Netplan generates configuration for systemd-networkd; NetworkManager means the generated settings are consumed by NetworkManager. If no renderer is specified, the distribution’s default applies, so check the Ubuntu edition and its documentation before making a persistent change.
Disable DHCPv6 without claiming to disable IPv6
For an interface managed by Netplan, dhcp6: false stops DHCPv6 address configuration for that interface. It does not necessarily stop router advertisements, static IPv6 addresses, link-local IPv6, or other IPv6 behavior. Treat it as a DHCPv6 choice, not as an equivalent to ipv6.disable=1 or NetworkManager’s ipv6.method disabled.
A minimal illustrative section can look like this, with the real interface name and existing options retained:
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ethernets:
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dhcp6: falseApply Netplan using the workflow appropriate to your installation after checking the YAML carefully. A syntax or indentation error can prevent the intended network configuration from being generated.
Understand link-local: [ ]
Netplan documents link-local: [ ] as disabling link-local addresses. This is broader than merely declining DHCPv6 and can affect link-local behavior for the interface; it is not a complete protocol-wide IPv6 switch. Use it only when you specifically need to suppress link-local address assignment and understand the effect on the interface.
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If the requirement is “no IPv6 on this host,” use the sysctl or GRUB approach. If the requirement is “this one NetworkManager profile must not use IPv6,” set that profile’s ipv6.method to disabled. Netplan’s DHCP and link-local controls should not be presented as substitutes for either scope.
Verification checklist after any method
- Run
ip aand inspect each relevant interface forinet6addresses. - For sysctl changes, read the relevant files in
/proc/sys/net/ipv6/conf/and confirm the intended values. - For NetworkManager, display the profile with
nmcli connection show, checkipv6.method, and reactivate the profile if it was not reconnected. - For GRUB, verify only after rebooting; editing the defaults file and running no reboot does not change the current kernel.
- Test the application or route that motivated the change, because removing an address does not by itself prove that every service has adopted the new configuration.
Troubleshooting common results
IPv6 addresses remain after a sysctl command
Confirm that all three flags were set, not just all. Check the values under /proc/sys/net/ipv6/conf/, then reconnect the affected interface or restart the relevant network service if it retained an old profile state. If the values return to 0 after a restart, the change was runtime-only or another persistent configuration is overriding it.
The setting disappears after reboot
Runtime commands are intentionally temporary. Put the flags in /etc/sysctl.conf or an appropriate /etc/sysctl.d/ file and reload them. If you intended a kernel-level policy, use the GRUB parameter and rebuild the menu with sudo update-grub before rebooting.
One connection still has IPv6 while another does not
That is expected when using NetworkManager profiles. Check each profile separately with nmcli connection show; changing one profile does not change the others. Apply ipv6.method disabled to every profile that must avoid IPv6, or use a host-wide sysctl or GRUB method when the policy is global.
Netplan changes do not produce the expected result
Check the renderer and the specific YAML file that owns the interface. dhcp6: false only controls DHCPv6, while link-local, router-advertised, static, or kernel-level IPv6 behavior may remain. If the requirement is complete IPv6 suppression, move to the method whose scope matches that requirement instead of stacking unrelated Netplan options.
A remote session drops during the change
NetworkManager profile reactivation and rebooting through GRUB both interrupt connectivity. Use local console access, an out-of-band console, or a second connection before applying a change to the interface carrying your administrative session. Keep the rollback command or edited line available before disconnecting.
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- Testing a suspected IPv6 issue now: run the three runtime
sysctlcommands, verify withip a, and restore the values when finished. - Keeping IPv6 off across normal reboots: save the three flags in sysctl configuration and reload them.
- Preventing IPv6 from starting at all: add
ipv6.disable=1to GRUB, runsudo update-grub, and reboot. - Restricting only one saved connection: set that NetworkManager profile to
ipv6.method disabledand reactivate it. - Controlling DHCPv6 or link-local behavior on a Netplan interface: edit the authoritative Netplan YAML, but do not describe those options as a complete IPv6 disable.
Keep a record of the original profile method, sysctl file, or GRUB command line. That makes rollback precise and prevents a temporary diagnostic setting from becoming an unexplained permanent networking change.
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