# This document will have the list of commands that could be
# used for troubleshooting linux networking purposes.

$ ifconfig
The ifconfig command without any arguments gives you all the 
active interfaces on your system. Interfaces will not appear 
if they are shut down, with -a will show all the info.
---------

Testing Link Status from the Command Line:
==========================================
Both the mii-tool and ethtool commands command will provide 
reports on the link status and duplex settings for supported NICs
When used without any switches, the mii-tool gives a very brief 
report. Use it with the -v switch because it provides more 
information on the supported autonegotiation speeds of the NIC and 
this can be useful in troubleshooting speed and duplex issues.

The ethtool command provides much more information than mii-tool and 
should be your command of choice, especially because mii-tool will be 
soon deprecated in Linux. In both of the following examples the NICs 
are operating at 100Mbps, full duplex and the link is ok. 

$ mii-tool -v enp5s0f0


$ ethtool enp5s0f0

----------------------------
Viewing NIC Errors:
===================
Errors are a common symptom of slow connectivity due to poor 
configuration or excessive bandwidth utilization. They should always 
be corrected whenever possible. Error rates in excess of 0.5% can 
result in noticeable sluggishness
 # Ifconfig Error Output
 $ ifconfig
    RX packets:2924 errors:0 dropped:0 overruns:0 frame:0
    TX packets:2287 errors:0 dropped:0 overruns:0 carrier:0
    
 # ethtool Error Output: The ethtool command can provide a much more 
 detailed report when used with the -S switch.
 $ ethtool -S enp5s0f0

 # netstat Error Output: The netstat command is very versatile and can 
 provide a limited report when used with the -i switch. This is useful 
 for systems where mii-tool or ethtool are not available.
 $ netstat -i

---------------------------------
How to See MAC Addresses:
=========================



General Notes:
DHCP clients automatically give their NICs and IP address starting 
with 169.254.x.x until they can make contact with their DHCP server. 
When contact is made they reconfigure their IP addresses to the 
values provided by the DHC server. An interface with a 169.254.x.x 
address signifies a failure to communicate with the DHCP server. 
Check your cabling, routing and DHCP server configuration to rectify 
such a problem. 


References:
Network troubleshooting:
- http://www.linuxhomenetworking.com/wiki/index.php/Quick_HOWTO_:_Ch04_:_Simple_Network_Troubleshooting#.WAkqxrMsFQI