On Debian 13, changing the external IPv6 address typically involves configuring your network interface or router, depending on whether the IPv6 address is assigned by your ISP (Internet Service Provider) or statically configured. Here’s how you can approach it:

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1. Check Current IPv6 Configuration

First, verify your current IPv6 address and network interface:

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ip -6 addr show

or

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ifconfig -a | grep inet6

Look for the interface connected to the external network (e.g., eth0, ens33, or enp0s3).

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2. Determine How IPv6 is Assigned

• Dynamic (SLAAC or DHCPv6): If your ISP assigns IPv6 dynamically (common for home connections), you cannot manually set the external IPv6 address—it is managed by your ISP or router.

  • To influence the assignment, you may need to:
    • Configure your router (if you control it) to request a specific prefix or use a static assignment.
    • Contact your ISP to request a static IPv6 block.

• Static IPv6: If you have a static IPv6 block (common for servers or business connections), you can manually configure it.

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3. Configure Static IPv6 on Debian

If you have a static IPv6 address, edit your network interface configuration.

Using netplan (Debian 13 default)

Debian 13 uses netplan for network configuration. Edit the relevant YAML file in /etc/netplan/ (e.g., 01-netcfg.yaml):

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network:
  version: 2
  renderer: networkd
  ethernets:
    ens33:  # Replace with your interface name
      dhcp6: no
      addresses:
        - "2001:db8::1/64"  # Replace with your static IPv6 address
      gateway6: "2001:db8::ffff"  # Replace with your IPv6 gateway
      nameservers:
        addresses:
          - "2001:4860:4860::8888"  # Example: Google DNS
          - "2001:4860:4860::8844"

Apply the changes:

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sudo netplan apply

Using ifconfig (Legacy)

If using ifconfig, add the IPv6 address temporarily:

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sudo ip -6 addr add 2001:db8::1/64 dev ens33

To make it persistent, add the command to /etc/rc.local or use a network manager like systemd-networkd.

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4. Configure IPv6 on Your Router

If your Debian machine is behind a router:

1. Log in to your router’s admin panel.
2. Look for IPv6 settings (often under WAN or LAN).
3. Enable static IPv6 or prefix delegation if your ISP supports it.
4. Assign the desired IPv6 address or prefix to your router, then configure Debian to use a static address within that prefix.

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5. Verify the New IPv6 Address

Check if the new IPv6 address is active:

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ip -6 addr show

Test connectivity:

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ping6 ipv6.google.com

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6. Troubleshooting

• No IPv6 connectivity? Ensure your ISP supports IPv6 and that your router is properly configured.
• Firewall rules: If you use ufw or iptables, ensure IPv6 traffic is allowed:

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  sudo ufw allow in on ens33 to any

• Restart networking:

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  sudo systemctl restart systemd-networkd

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Key Notes

• External IPv6 is often managed by your ISP or router. If you’re on a home connection, you likely cannot change it directly on Debian.
• For servers, contact your hosting provider to assign a static IPv6 address.
• If you’re using a cloud provider (e.g., AWS, OVH), check their documentation for IPv6 assignment.

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