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LO(4)		       FreeBSD Kernel Interfaces Manual			 LO(4)

     lo	-- software loopback network interface

     device loop

     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	with the appropriate ioctl(2) commands for
     corresponding address families.  The loopback interface should be the
     last interface configured,	as protocols may use the order of configura-
     tion as an	indication of priority.	 The loopback should never be config-
     ured first	unless no hardware interfaces exist.

     If	the transmit checksum offload capability flag is enabled on a loopback
     interface,	checksums will not be generated	by IP, UDP, or TCP for packets
     sent on the interface.

     If	the receive checksum offload capability	flag is	enabled	on a loopback
     interface,	checksums will not be validated	by IP, UDP, or TCP for packets
     received on the interface.

     By	default, both receive and transmit checksum flags will be enabled, in
     order to avoid the	overhead of checksumming for local communication where
     data corruption is	unlikely.  If transmit checksum	generation is dis-
     abled, then validation should also	be disabled in order to	avoid packets
     being dropped due to invalid checksums.

     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

     inet(4), intro(4)

     The lo device appeared in 4.2BSD.	The current checksum generation	and
     validation	avoidance policy appeared in FreeBSD 8.0.

FreeBSD	13.0		       January 25, 2012			  FreeBSD 13.0


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