1*47675Scael.\" Copyright (c) 1983, 1991 The Regents of the University of California. 236752Sbostic.\" All rights reserved. 320732Smckusick.\" 443581Strent.\" %sccs.include.redist.man% 520732Smckusick.\" 6*47675Scael.\" @(#)lo.4 6.6 (Berkeley) 03/28/91 736752Sbostic.\" 8*47675Scael.Dd 9*47675Scael.Dt LO 4 10*47675Scael.Os BSD 4.2 11*47675Scael.Sh NAME 12*47675Scael.Nm lo 13*47675Scael.Nd software loopback network interface 14*47675Scael.Sh SYNOPSIS 15*47675Scael.Sy pseudo-device 16*47675Scael.Nm loop 17*47675Scael.Sh DESCRIPTION 1820732SmckusickThe 19*47675Scael.Nm loop 2020732Smckusickinterface is a software loopback mechanism which may be 2120732Smckusickused for performance analysis, software testing, and/or local 2228257Skarelscommunication. 2328257SkarelsAs with other network interfaces, the loopback interface must have 2428257Skarelsnetwork addresses assigned for each address family with which it is to be used. 2528257SkarelsThese addresses 26*47675Scaelmay be set or changed with the 27*47675Scael.Dv SIOCSIFADDR 28*47675Scael.Xr ioctl 2 . 2928343SkarelsThe loopback interface should be the last interface configured, 3028343Skarelsas protocols may use the order of configuration as an indication of priority. 31*47675ScaelThe loopback should 32*47675Scael.Em never 33*47675Scaelbe configured first unless no hardware 3428343Skarelsinterfaces exist. 35*47675Scael.Sh DIAGNOSTICS 36*47675Scael.Bl -diag 37*47675Scael.It lo%d: can't handle af%d. 38*47675ScaelThe interface was handed 3920732Smckusicka message with addresses formatted in an unsuitable address 4020732Smckusickfamily; the packet was dropped. 41*47675Scael.El 42*47675Scael.Sh SEE ALSO 43*47675Scael.Xr intro 4 , 44*47675Scael.Xr inet 4 , 45*47675Scael.Xr ns 4 46*47675Scael.Sh HISTORY 47*47675ScaelThe 48*47675Scael.Nm 49*47675Scaeldevice appeared in 50*47675Scael.Bx 4.2 . 51*47675Scael.Sh BUGS 5228257SkarelsPrevious versions of the system enabled the loopback interface 5328257Skarelsautomatically, using a nonstandard Internet address (127.1). 5428343SkarelsUse of that address is now discouraged; a reserved host address 5528343Skarelsfor the local network should be used instead. 56