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 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%d: can't handle af%d.
- The interface was handed a message with addresses
formatted in an unsuitable address family; the packet was dropped.
inet(4),
intro(4)
The
lo device appeared in
4.2BSD. The current checksum generation and validation
avoidance policy appeared in
FreeBSD 8.0.