1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)lo.4 8.1 (Berkeley) 06/05/93 7.\" 8.Dd 9.Dt LO 4 10.Os BSD 4.2 11.Sh NAME 12.Nm lo 13.Nd software loopback network interface 14.Sh SYNOPSIS 15.Sy pseudo-device 16.Nm loop 17.Sh DESCRIPTION 18The 19.Nm loop 20interface is a software loopback mechanism which may be 21used for performance analysis, software testing, and/or local 22communication. 23As with other network interfaces, the loopback interface must have 24network addresses assigned for each address family with which it is to be used. 25These addresses 26may be set or changed with the 27.Dv SIOCSIFADDR 28.Xr ioctl 2 . 29The loopback interface should be the last interface configured, 30as protocols may use the order of configuration as an indication of priority. 31The loopback should 32.Em never 33be configured first unless no hardware 34interfaces exist. 35.Sh DIAGNOSTICS 36.Bl -diag 37.It lo%d: can't handle af%d. 38The interface was handed 39a message with addresses formatted in an unsuitable address 40family; the packet was dropped. 41.El 42.Sh SEE ALSO 43.Xr intro 4 , 44.Xr inet 4 , 45.Xr ns 4 46.Sh HISTORY 47The 48.Nm 49device appeared in 50.Bx 4.2 . 51.Sh BUGS 52Previous versions of the system enabled the loopback interface 53automatically, using a nonstandard Internet address (127.1). 54Use of that address is now discouraged; a reserved host address 55for the local network should be used instead. 56