FreeBSD manual
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LO(4) FreeBSD Kernel Interfaces Manual LO(4)
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.
FreeBSD 14.0-RELEASE-p11 January 25, 2012 FreeBSD 14.0-RELEASE-p11