To change the external IPv6 address on a Debian 13 VPS hosted on OVH, you need to follow these steps. OVH typically assigns IPv6 addresses via SLAAC (Stateless Address Autoconfiguration) or DHCPv6, but you can manually configure a static IPv6 address if OVH provides a dedicated IPv6 block.

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Prerequisites

1. Check OVH IPv6 Assignment

   • Log in to your OVH Cloud Control Panel.
   • Navigate to Public Cloud > Instances > Your VPS > Network.
   • Verify if OVH has assigned a static IPv6 block (e.g., /64 or /128) to your VPS.
   • If not, you may need to request an IPv6 block from OVH support.

2. SSH Access

   • Ensure you have root or sudo access to your VPS.

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Steps to Configure IPv6 on Debian 13

1. Check Current IPv6 Configuration

Run the following command to see your current IPv6 addresses:

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ip -6 addr show

or

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ifconfig -a | grep inet6

2. Identify Your Network Interface

Find your primary network interface (usually eth0, ens3, or enp0s3):

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ip link show

3. Configure Static IPv6 Address

If OVH provides a static IPv6 block, you can manually assign an address.

Option A: Temporary Configuration (for testing)

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sudo ip -6 addr add <IPv6_ADDRESS>/64 dev <INTERFACE>

Example:

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sudo ip -6 addr add 2001:db8::1/64 dev eth0

Option B: Permanent Configuration (via Netplan or /etc/network/interfaces)

Since Debian 13 uses Netplan by default, edit the Netplan config:

1. Open the Netplan configuration file:

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   sudo nano /etc/netplan/01-netcfg.yaml

   (or /etc/netplan/50-cloud-init.yaml if using cloud-init)

2. Add an IPv6 address (replace <IPv6_ADDRESS> and <INTERFACE>):

   yaml
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   network:
     version: 2
     renderer: networkd
     ethernets:
       <INTERFACE>:
         dhcp6: false
         addresses:
           - <IPv6_ADDRESS>/64
         gateway6: <IPv6_GATEWAY>  # If OVH provides a gateway

   Example:

   yaml
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   network:
     version: 2
     renderer: networkd
     ethernets:
       eth0:
         dhcp6: false
         addresses:
           - 2001:db8::1/64
         gateway6: 2001:db8::ff

3. Apply the changes:

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   sudo netplan apply

Option C: Using /etc/network/interfaces (Legacy)

If your system uses ifupdown (older Debian versions), edit:

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sudo nano /etc/network/interfaces

Add:

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iface <INTERFACE> inet6 static
    address <IPv6_ADDRESS>/64
    netmask 64
    gateway <IPv6_GATEWAY>

Then restart networking:

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sudo systemctl restart networking

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4. Verify the New IPv6 Address

Check if the new IPv6 is assigned:

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ip -6 addr show

Test connectivity:

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ping6 ipv6.google.com

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5. Update OVH Firewall (if applicable)

If OVH has a network firewall, ensure it allows traffic on the new IPv6 address:

• Go to OVH Control Panel > Network > Firewall.
• Add rules for ICMPv6, TCP, and UDP as needed.

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6. Troubleshooting

• If IPv6 is not working:

  • Ensure OVH has routed the IPv6 block to your VPS.
  • Check for firewall rules blocking IPv6.
  • Verify gateway connectivity (ping6 <IPv6_GATEWAY>).

• If using DHCPv6/SLAAC: OVH may automatically assign IPv6 via router advertisements (RA). If you want a static address, disable SLAAC in /etc/sysctl.conf:

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  net.ipv6.conf.all.autoconf=0
  net.ipv6.conf.default.autoconf=0

  Then apply:

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  sudo sysctl -p

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Final Notes

• OVH may not allow arbitrary IPv6 changes—ensure the address is part of your allocated block.
• If you don’t have a static IPv6 block, contact OVH support to request one.
• For additional IPv6 addresses, OVH may require justification (e.g., hosting multiple services).

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Would you like help verifying your OVH IPv6 allocation or troubleshooting a specific issue?