IP Aliasing: Assigning Multiple IPs to One Network Card

Introduction: The Digital Schizophrenia

Normally, one hardware Network Interface Card (NIC) gets one IP address. But what if you are hosting two websites on the same Linux server that require separate SSL certificates natively attached to dedicated IPs? You use IP Aliasing.

Virtual Interfaces

In Linux, you have your main physical interface, like `eth0`. With aliasing, you can create a 'virtual' interface on top of it, named `eth0:1`. You can then assign `eth0:1` a completely different IP address. The single physical cable into the server will now happily listen for and respond to traffic destined for either of the two IP addresses.

Conclusion

IP Aliasing maximizes the use of a physical server, allowing complex virtual topologies to exist on extremely simple hardware. Test your server's responding IPs here.