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LO(4)			    BSD Programmer's Manual			 LO(4)

NAME
     lo - software loopback network interface

SYNOPSIS
     pseudo-device loop count

DESCRIPTION
     The loop interface is a software loopback mechanism which may be used for
     performance analysis, software testing, and/or local communication.  As
     with other network interfaces, the loopback interface must have network
     addresses assigned for each address family with which it is to be used.
     These addresses may be set or changed with the program ifconfig(8).  The
     loopback interface should be the last interface configured, as protocols
     may use the order of configuration as an indication of priority.  The
     loopback interface should never be configured first unless no hardware
     interfaces exist.

     The loopback interface may be configured with any number of addresses,
     this is frequently used for supporting virtual hosts.  While not strictly
     necessary, it is possible to define multiple loopback interfaces to fa-
     cilitate the grouping of virtual addresses.  This may be accomplishd by
     specifying the count at kernel config time, modifying the nloif variable
     in the system with bpatch(1) before booting, or by modifying the
     net.link_layer.generic.lo.numif variable with sysctl(1).

NOTES
     Previous versions of the system enabled the loopback interface automati-
     cally, using a nonstandard Internet address (127.1).  The address must
     now be set at boot time.  The address 127.1 may be used, as network 127
     is now designated as the loopback network.

DIAGNOSTICS
     lo%d: can't handle af%d.  The interface was handed a message with ad-
     dresses formatted in an unsuitable address family; the packet was
     dropped.

SEE ALSO
     intro(4),	inet(4),  ns(4),  ifconfig(8)

HISTORY
     The lo device appeared in 4.2BSD.

4.2 Berkeley Distribution	 June 5, 1993				     1

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