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