On early BSD systems, network interfaces were static objects created at kernel compile time. Today the situation has changed dramatically. PC Card, USB, and other removable buses allow hardware interfaces to arrive and depart at run time. Pseudo-device cloning also allows pseudo-devices to be created dynamically. Additionally, in FreeBSD and Dragonfly, interfaces can be renamed by the administrator. With these changes, interfaces are now dynamic objects which may appear, change, or disappear at any time. This dynamism invalidates a number of assumptions that have been made in the kernel, in external programs, and even in standards such as SNMP. This paper explores the history of the transition of network interfaces from static to dynamic. Issues raised by these changes are discussed and possible solutions suggested.
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