
ifupdown-extra information
--------------------------

This package provides a set of scripts adding tests when interfaces are
configured to try to detect some common network errors when an interface is
started these include:

 - Checking if the network interface cable is plugged in or not
 - Checking if there exists another system in the network with the same IP
   address
 - Checking if the default gateway assigned to the interface is reachable or not

Additional tests can be included, even for specific type of interfaces (e.g.
for Serial lines or for WAN interfaces). If you have any idea for a test please
submit it as a bug report to the package.


Known limitations:
------------------

---------------
Interface names
---------------

Starting with v197, systemd/udev creates predictable network interface names
for all local Ethernet, WLAN and WWAN interfaces. However, system
administrators can adjust the names for interfaces to match their preference
(e.g. setup a system rule so that an interface is named 'internet' or 'dmz').
The existing scripts only operate on known names and restrict some operations
(to avoid errors) to specific type of interfaces. 

For example, when a network cable is checked this is only done on Ethernet
interfaces (i.e. named 'ethxx' or 'enxxx') as the ethtool or mii-tool only
works on them. 

This means that if an administrator has changed the naming of interfaces in a
system some of the scripts will stop working.

For more information please refer to:

Debian/Wiki 
    https://wiki.debian.org/NetworkInterfaceNames
Freedesktop.org - Predictable Network Interfaces:
    https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/
systemd.net-naming scheme: https://www.freedesktop.org/software/systemd/man/systemd.net-naming-scheme.html


------------------
Network link checks
------------------

The script that tests the network link is run inmediately after an interface is
administratively configured up. However, the underlying hardware sometime it
takes some time to establish and negotiate a link. This is heavily dependant on
the hardware itself and the system it is connected to (e.g. if auto negotiation
of an interface is enabled or the duplex/mode are forced in the interface). 

Due to this time interval for the link to fully stablise it is possible that
the check-network-cable might generate false negative error messages on
systems. 

If this is your case, you are encourage to disable the script by editing
/etc/default/network-test and changing the variable DO_CABLETEST to 'no'

----------
Javier Fernández-Sanguino
Sat, 19 Sep 2020 09:02:48 +0200


