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.

Debian                                          January 25, 2012                                           LO(4)