ultrix man page for lo

lo(4)							     Kernel Interfaces Manual							     lo(4)

Name
       lo - loop network interface

Syntax
       pseudo-device loop

Description
       The  interface  is  a  software loopback mechanism that can be used for performance analysis, software testing, and/or local communication.
       By default, the loopback interface is accessible at address 127.0.0.1 (nonstandard); this address  may  be  changed  with  the  SIOCSIFADDR
       ioctl.

Diagnostics
       lo%d: can't handle af%d
       The interface was handed a message with addresses formatted in an unsuitable address family; the packet was dropped.

See Also
       intro(4n), inet(4f)

																	     lo(4)