bsd/man/man4/lo.4

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  34 .\"     @(#)lo.4        8.1 (Berkeley) 6/5/93
  35 .\"
  36 .Dd June 5, 1993
  37 .Dt LO 4
  38 .Os BSD 4.2
  39 .Sh NAME
  40 .Nm lo
  41 .Nd software loopback network interface
  42 .Sh SYNOPSIS
  43 .Sy pseudo-device
  44 .Nm loop
  45 .Sh DESCRIPTION
  46 The
  47 .Nm loop
  48 interface is a software loopback mechanism which may be
  49 used for performance analysis, software testing, and/or local
  50 communication.
  51 As with other network interfaces, the loopback interface must have
  52 network addresses assigned for each address family with which it is to be used.
  53 These addresses
  54 may be set or changed with the
  55 .Dv SIOCSIFADDR
  56 .Xr ioctl 2 .
  57 The loopback interface should be the last interface configured,
  58 as protocols may use the order of configuration as an indication of priority.
  59 The loopback should
  60 .Em never
  61 be configured first unless no hardware
  62 interfaces exist.
  63 .Sh DIAGNOSTICS
  64 .Bl -diag
  65 .It lo%d: can't handle af%d.
  66 The interface was handed
  67 a message with addresses formatted in an unsuitable address
  68 family; the packet was dropped.
  69 .El
  70 .Sh SEE ALSO
  71 .Xr inet 4 ,
  72 .Xr intro 4 ,
  73 .Xr ns 4
  74 .Sh HISTORY
  75 The
  76 .Nm
  77 device appeared in
  78 .Bx 4.2 .
  79 .Sh BUGS
  80 Previous versions of the system enabled the loopback interface
  81 automatically, using a nonstandard Internet address (127.1).
  82 Use of that address is now discouraged; a reserved host address
  83 for the local network should be used instead.