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lo(7)
NAME
  lo - Software loopback network interface

SYNOPSIS
  pseudo-device loop

DESCRIPTION
  The loopback interface is a software loopback mechanism which is used for
  performance analysis, software testing, and/or local communication.  As
  with other network interfaces, the loopback interface must have network
  addresses assigned for each address family with which it is to be used.
  These addresses may be set or changed with the SIOCSIFADDR ioctl.  The
  loopback interface should be the last interface configured, as protocols
  may use the order of configuration as an indication of priority.  The
  loopback should never be configured first unless no hardware interfaces
  exist.

NOTES
  Previous versions of the UNIX system enabled the loopback interface
  automatically, using a nonstandard Internet address (127.1).	Use of that
  address is now discouraged; a reserved host address for the local network
  should be used instead.

ERRORS
  lon: can't handle afn
	    The interface was handed a message with addresses formatted in an
	    unsuitable address family; the packet was dropped.

RELATED INFORMATION
  Files: netintro(7), inet(7), ns(7)