IP and IPv6 Configuration

This document explains how to add extra IPv4 addresses and the IPv6 subnet to the operating system on SistemDC servers, how to verify them and how to set an rDNS (PTR) record. It includes examples for Linux (Ubuntu, Debian, AlmaLinux, Rocky Linux) and Windows Server.

#What is included with each service?

Prices exclude VAT. Full prices: VDS addon prices · dedicated server addon prices.

#Where to find your addresses

Your assigned IPv4 and IPv6 addresses, netmask and gateway are listed on the service details page in the client area and are also sent by e-mail at first delivery. Addresses added later appear on the same page.

#IPv6: what you need to know

• Static configuration: our network has no automatic address assignment (SLAAC / Router Advertisements). The IPv6 address and gateway are written into the operating system manually (statically).
• Gateway: always fe80::1. As a link-local address, the gateway is set together with the network interface (e.g. fe80::1%eth0).
• Prefix: you receive a /64 and may use every address in it. On a VDS the IPv6 address shown in the service details is configured at setup.
• Do not block ICMPv6: IPv6 relies on ICMPv6 for Neighbor Discovery. If ICMPv6 is blocked entirely in the firewall, IPv6 stops working.
• European VDS: IPv6 is not offered on France and Germany VDS.

#Adding extra IPv4 and IPv6 on Linux

First find the name of the network interface (such as eth0 or ens18). The examples below assume interface eth0, primary IPv4 203.0.113.10/24, gateway 203.0.113.1, extra IPv4 203.0.113.11 and IPv6 block 2001:db8:241:1000::/64.

ip -br link
ip -br addr

#Ubuntu (netplan)

Open the existing file in /etc/netplan/ (ls /etc/netplan/) and add the addresses to the addresses list. Edit the existing file instead of creating a new one.

network:
  version: 2
  ethernets:
    eth0:
      addresses:
        - 203.0.113.10/24            # primary IPv4
        - 203.0.113.11/24            # extra IPv4
        - 2001:db8:241:1000::1/64    # IPv6
      routes:
        - to: default
          via: 203.0.113.1
        - to: default
          via: fe80::1
      nameservers:
        addresses: [1.1.1.1, 8.8.8.8, 2606:4700:4700::1111]

Test the change with netplan try: if you do not confirm within 120 seconds the setting is rolled back automatically, so you do not lose access. Press Enter to confirm if everything works.

sudo netplan try
sudo netplan apply

echo 'network: {config: disabled}' | sudo tee /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg

#Debian (ifupdown)

Add to the relevant interface in /etc/network/interfaces:

auto eth0
iface eth0 inet static
    address 203.0.113.10/24
    gateway 203.0.113.1
    up   ip addr add 203.0.113.11/24 dev eth0
    down ip addr del 203.0.113.11/24 dev eth0

iface eth0 inet6 static
    address 2001:db8:241:1000::1/64
    gateway fe80::1

Apply with sudo systemctl restart networking. This briefly interrupts the connection; running it from the console is recommended.

#AlmaLinux / Rocky Linux (NetworkManager)

Find the connection name and add the addresses with nmcli:

nmcli con show
sudo nmcli con mod "System eth0" +ipv4.addresses 203.0.113.11/24
sudo nmcli con mod "System eth0" ipv6.method manual ipv6.addresses 2001:db8:241:1000::1/64 ipv6.gateway fe80::1
sudo nmcli con up "System eth0"

#Testing without making it permanent

The commands below add the address immediately but it is lost on reboot; once it works, switch to the permanent method above.

sudo ip addr add 203.0.113.11/24 dev eth0
sudo ip -6 addr add 2001:db8:241:1000::1/64 dev eth0
sudo ip -6 route add default via fe80::1 dev eth0

#Adding extra IPv4 and IPv6 on Windows Server

Open PowerShell as administrator and find the interface name (usually Ethernet). Do not change the primary IP settings; only add the extra addresses.

Get-NetAdapter
netsh interface ipv4 add address "Ethernet" 203.0.113.11 255.255.255.0
netsh interface ipv6 add address "Ethernet" 2001:db8:241:1000::1/64
netsh interface ipv6 add route ::/0 "Ethernet" fe80::1

From the graphical interface: Network Connections → adapter → Properties → Internet Protocol Version 4 → Advanced → IP addresses → Add. Windows Firewall does not answer ping by default; to test with ping from outside, allow ICMP:

New-NetFirewallRule -DisplayName "ICMPv4 Echo" -Protocol ICMPv4 -IcmpType 8 -Action Allow
New-NetFirewallRule -DisplayName "ICMPv6 Echo" -Protocol ICMPv6 -IcmpType 128 -Action Allow

#IP blocks and IPv6 on dedicated servers

• Extra IPv4 block: the block details (network address, usable addresses, netmask and gateway) are sent at delivery and shown in the service details. Add the usable addresses to the primary interface with the methods above, using the netmask and gateway provided.
• IPv6: the /64 is not configured automatically on dedicated servers. Open a support ticket; you receive your /64 and gateway details and then set them up with the examples in this document.
• Virtualisation: if you installed Proxmox VE or VMware ESXi, you give extra IPs to virtual machines through a bridge interface; the addresses must still come from the block assigned to you.

#Verification

ip -br addr
ping -c 3 -I 203.0.113.11 203.0.113.1
ping -6 -c 3 2606:4700:4700::1111
curl -4 https://ifconfig.co
curl -6 https://ifconfig.co

If an extra IP does not answer from outside: the gateway's cache may be stale. Ping the gateway from the new address (ping -I <extra-ip> <gateway>); this refreshes the entry. To test from our network you can use the Looking Glass.

#rDNS (PTR)

Reverse DNS for your IPv4 and IPv6 addresses is set in the rDNS section of the service details in the client area. If the field is not there, open a support ticket with the IP address and the hostname you want.

• Use a fully qualified hostname (e.g. mail.example.com).
• If you send e-mail, the hostname's A (IPv4) or AAAA (IPv6) record must point to the same IP; a mismatched PTR hurts deliverability.
• Verify with dig -x 203.0.113.11 +short

More: Knowledge base: Network

#Usage rules

• Use only the IP addresses assigned to you. Using an unassigned address breaches the Terms of Service; on a VDS that traffic is blocked by the network.
• For extra IP requests a usage justification may be required under RIPE rules.
• IPv4 prices and limits: VDS · dedicated server.

#Frequently asked questions