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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.