1*61598Sbostic.\" Copyright (c) 1983, 1991, 1993 2*61598Sbostic.\" The Regents of the University of California. All rights reserved. 320732Smckusick.\" 443581Strent.\" %sccs.include.redist.man% 520732Smckusick.\" 6*61598Sbostic.\" @(#)lo.4 8.1 (Berkeley) 06/05/93 736752Sbostic.\" 847675Scael.Dd 947675Scael.Dt LO 4 1047675Scael.Os BSD 4.2 1147675Scael.Sh NAME 1247675Scael.Nm lo 1347675Scael.Nd software loopback network interface 1447675Scael.Sh SYNOPSIS 1547675Scael.Sy pseudo-device 1647675Scael.Nm loop 1747675Scael.Sh DESCRIPTION 1820732SmckusickThe 1947675Scael.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 2647675Scaelmay be set or changed with the 2747675Scael.Dv SIOCSIFADDR 2847675Scael.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. 3147675ScaelThe loopback should 3247675Scael.Em never 3347675Scaelbe configured first unless no hardware 3428343Skarelsinterfaces exist. 3547675Scael.Sh DIAGNOSTICS 3647675Scael.Bl -diag 3747675Scael.It lo%d: can't handle af%d. 3847675ScaelThe interface was handed 3920732Smckusicka message with addresses formatted in an unsuitable address 4020732Smckusickfamily; the packet was dropped. 4147675Scael.El 4247675Scael.Sh SEE ALSO 4347675Scael.Xr intro 4 , 4447675Scael.Xr inet 4 , 4547675Scael.Xr ns 4 4647675Scael.Sh HISTORY 4747675ScaelThe 4847675Scael.Nm 4947675Scaeldevice appeared in 5047675Scael.Bx 4.2 . 5147675Scael.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