How to enable or disable IPv6

Topic: Networking basics

Enable or disable IPv6 on Linux via sysctl (net.ipv6.conf.all.disable_ipv6 and per-interface), netplan, or NetworkManager. Use this when you need to turn off IPv6 for compatibility or security, or to turn it back on after it was disabled. Test with ping6 and ip -6 addr.

Intent: How-to

Quick answer

  • Disable globally: sysctl -w net.ipv6.conf.all.disable_ipv6=1; make persistent in /etc/sysctl.d/ (e.g. net.ipv6.conf.all.disable_ipv6 = 1). Reboot or apply with sysctl -p.
  • Enable: set disable_ipv6=0 or remove the override; ensure netplan or NM has IPv6 addresses or method auto if you use DHCPv6; ip -6 addr to verify.
  • Per-interface: net.ipv6.conf.IFACE.disable_ipv6; disable on one interface only if you want IPv6 on others; some apps may still prefer IPv4 if IPv6 is broken, so test both.

Prerequisites

Steps

  1. Disable IPv6 globally (temporary)

    sysctl -w net.ipv6.conf.all.disable_ipv6=1; IPv6 addresses disappear from interfaces; no reboot needed but lost on reboot.

  2. Disable IPv6 persistently

    Create /etc/sysctl.d/99-disable-ipv6.conf with line net.ipv6.conf.all.disable_ipv6 = 1; run sysctl -p /etc/sysctl.d/99-disable-ipv6.conf; or reboot.

  3. Enable IPv6 again

    Set net.ipv6.conf.all.disable_ipv6=0 or remove the sysctl override file; run sysctl -p; configure IPv6 in netplan (addresses and optionally gateway) or NM (ipv6.method auto or manual); ip -6 addr to confirm.

  4. Verify

    ip -6 addr (or ip addr | grep inet6); ping6 -c 2 hostname-or-ipv6; if disabled, no inet6 addresses and ping6 fails; if enabled, addresses present and ping6 works when route exists.

Summary

Enable or disable IPv6 globally (or per interface) with sysctl; make it persistent in /etc/sysctl.d/. When enabling, configure addresses and routes in netplan or NetworkManager. Use this when you need to turn IPv6 off for compatibility or turn it on for dual-stack.

Prerequisites

Steps

Step 1: Disable IPv6 globally (temporary)

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

IPv6 addresses are removed from interfaces. Change is lost on reboot.

Step 2: Disable IPv6 persistently

Create /etc/sysctl.d/99-disable-ipv6.conf:

net.ipv6.conf.all.disable_ipv6 = 1

Run sudo sysctl -p /etc/sysctl.d/99-disable-ipv6.conf or reboot.

Step 3: Enable IPv6 again

Set net.ipv6.conf.all.disable_ipv6 = 0 or remove the override file; run sysctl -p. In netplan or NM, add IPv6 addresses or set ipv6.method: auto (or manual). Then ip -6 addr should show addresses.

Step 4: Verify

ip -6 addr
ping6 -c 2 2001:4860:4860::8888

If disabled, no inet6 addresses; if enabled, addresses and ping6 work when routing allows.

Verification

  • With IPv6 disabled: no inet6 addresses; ping6 fails. With IPv6 enabled: addresses present and ping6 works when the path supports IPv6.

Troubleshooting

IPv6 still present after disable — Ensure net.ipv6.conf.all.disable_ipv6=1 is applied (sysctl -a | grep disable_ipv6); reboot to clear any stale state.

IPv6 not working when enabled — Check addresses and default route (ip -6 route); firewall may block IPv6; some networks do not route IPv6.

Next steps

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