Common Network Troubleshooting tools

common tools

------------

1. ifconfig

setting mtu size (by default mtu is set to 1500, replac xxxx with size wanted) sets the maximum transmission unit on the interface

# ifconfig eth0 mtu xxxx

set interface in promiscuous mode

- interfaces only receive packets that belong to that particulr nic. if you put the interface in promiscuous mode it will receive all the packets. this is useful to capture packets and analyze later

# ifconfig eth0 - promsic

How to Change the MAC address of Network Interface

To change the MAC (Media Access Control) address of an eth0 network interface, use the following command with argument “hw ether“. For example, see below.

[root@tecmint ~]# ifconfig eth0 hw ether AA:BB:CC:DD:EE:FF

These are the most useful commands for configuring network interfaces in Linux, for more information and usage of ifconfig command use the manpages like “man ifconfig” at the terminal. Check out some other networking utilities below.

2. ping

3. traceroute - network troubleshooting utility which shows number of hops taken to reach destination also determins packets traveling path.

4. netstat

5. dig

6. nslookup

7. route

8. host

9. arp

10. ethtool

#ethtool eth0

This above ethtool output displays ethernet card properties such as speed, wake on, duplex and the link detection status. Following are the three types of duplexes available.

Full duplex : Enables sending and receiving of packets at the same time. This mode is used when the ethernet device is connected to a switch.

Half duplex : Enables either sending or receiving of packets at a single point of time. This mode is used when the ethernet device is connected to a hub.

Auto-negotiation : If enabled, the ethernet device itself decides whether to use either full duplex or half duplex based on the network the ethernet device attached to.

11. iwconfig

12. hostname

other network utilities

***********************

Tcmpdump — a command-line packet capture and analyzer tool for monitoring network traffic.

Netstat — an open source command line network monitoring tool that monitors incoming and outgoing network packets traffic.

Wireshark — an open source network protocol analyzer that is used to troubleshoot network related issues.

Munin — a web based network and system monitoring application that is used to display results in graphs using rrdtool.

Cacti — a complete web based monitoring and graphing application for network monitoring.