bionic (4) lo.4freebsd.gz

NAME

     lo — software loopback network interface

SYNOPSIS

     device loop

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
     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 configuration as an indication of
     priority.  The loopback should never be configured 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
     disabled, then validation should also be disabled in order to avoid packets being dropped due to invalid
     checksums.

DIAGNOSTICS

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

SEE ALSO

     inet(4), intro(4)

HISTORY

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