IP addresses on our network are bound to the MAC address of the server's network interface. This is applied by default whenever an address is issued.
Why we do this
You have full control over your server, which includes the ability to configure any address you like on it. Without MAC binding, an address entered by mistake — a typo, or a configuration copied from another server — would be announced on the network and collide with whoever legitimately holds it. Binding means a misconfigured address simply does not work, instead of taking someone else's server offline.
It also protects your own addresses: nobody else on the network can take one over.
What it means in practice
For an ordinary server, nothing. The addresses issued to you work on your server's interface, and you never encounter the binding.
It becomes relevant when traffic needs to leave the server with a different MAC address than the host's own interface. That is the case with:
- virtual machines on your server, each with its own virtual interface and its own MAC;
- containers configured with bridged networking rather than NAT;
- a virtual router or firewall passing traffic on behalf of other machines.
In these configurations the address is configured correctly inside the virtual machine, and it still does not work — the traffic reaches our network with a MAC we have not authorised for that address.
If you plan to use virtualisation
Tell us when you order the server, or when you order additional addresses. We will configure the binding to suit the setup, and you avoid diagnosing a problem that has nothing to do with your own configuration.
If the server is already running and you are adding virtual machines now, open a ticket with our Technical Support department describing what you are building — how many machines, and whether they need their own public addresses. Doing this in advance takes minutes; working it out afterwards from the symptoms takes considerably longer.
Symptoms of an unauthorised MAC
The pattern is distinctive: the address is configured, ip addr shows it as present, but nothing reaches it from outside and it cannot reach out either. Traffic from the host works while traffic from the virtual machine does not. If that describes what you are seeing, this is very likely the cause rather than anything in your own network configuration.
See also Additional IP addresses for ordering addresses, and How to add an additional IP address on Linux for configuring them.
