In the Linux (or Unix) world, most network interfaces, such as eth0 and ppp0, are associated with a physical device that is in charge of transmitting and receiving data packets. However, some logical network interfaces don't feature any physical packet transmission. The most well-known examples of these "virtual" interfaces are the shaper and eql interfaces. This month, we'll look at how this kind of interface attaches to the kernel and to the packet-transmission mechanism.
