1LO(4)                      Kernel Interfaces Manual                      LO(4)
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NAME

6       lo - software loopback network interface
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SYNOPSIS

9       /sys/conf/SYSTEM:
10            NLOOP     1    # loop-back pseudo-device
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DESCRIPTION

13       The  loop  interface is a software loopback mechanism which may be used
14       for performance analysis, software testing, and/or local communication.
15       As with other network interfaces, the loopback interface must have net‐
16       work addresses assigned for each address family with which it is to  be
17       used.   These  addresses  may  be  set  or changed with the SIOCSIFADDR
18       ioctl.  The loopback interface should be the last interface configured,
19       as  protocols  may  use  the order of configuration as an indication of
20       priority.  The loopback should never  be  configured  first  unless  no
21       hardware interfaces exist.
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DIAGNOSTICS

24       lo%d:  can't  handle  af%d.   The  interface  was handed a message with
25       addresses formatted in an unsuitable address  family;  the  packet  was
26       dropped.
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SEE ALSO

29       intro(4N), inet(4F), ns(4F)
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BUGS

32       Previous versions of the system enabled the loopback interface automat‐
33       ically, using a nonstandard Internet  address  (127.1).   Use  of  that
34       address  is now discouraged; a reserved host address for the local net‐
35       work should be used instead.
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393rd Berkeley Distribution       August 1, 1987                           LO(4)