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1 Subject: Network Troubleshooting Tools Lecturer: Jirawat Thaenthong Organization: Faculty of Technology and Environment, PSU, Phuket Campus. Date: 19/5/60 Version: 1.0 Approved Objective: 1. Trainees study and practice network troubleshooting tools. 2. Trainees study case studies and discuss with the others. Instructions& Prerequisites: - Trainees should have basic skill of Linux commands. - Linux virtual machine (VirtualBox/VMware) Task 1: Practice basic network troubleshooting tools 1. Link detection/verification with ethtool With this command, we can do much more as follows: Auto-negotiation The speed of the device Display all NIC settings Display auto-negotiation, RX, and TX settings Display network statistics for a specific NIC Troubleshoot ethernet connections Blink the LED of a specific NIC 1.1. Install ethtool package. If you have already, skip this step. $ ethtool h ß Please verify if you have it or not. $ sudo apt install ethtool ßInstall ethtool Ubuntu Networking Part I Page 1

2 1.2. Verify how many network interfaces you have. $ ifconfig a ßList all network interfaces 1.3. Detect which network interface connected to LAN $ ethtool enp0s3 ßAssume this interface is connected to LAN. You will see Link detected: yes Ubuntu Networking Part I Page 2

3 1.4. Show the NIC statistics $ ethtool S enp0s3 If you find ethtool reporting-specific errors on a card, there's a problem Locating a specific NIC $ sudo ethtool p enp0s3 15 ßLED blinking on the specific NIC. It is useful if you have a server with multiple NICs, but you do know which one is correct. Ubuntu Networking Part I Page 3

4 1.6. Testing your NIC $ sudo ethtool t enp0s3 online Online - tests nvram and a link test Offline - tests register, memory, loopback, interrupt ß Some NIC does not support function Practice by yourself Ubuntu Networking Part I Page 4

5 2. IP addressing 2.1. When you assign network configuration with ifconfig and route command, If you no longer use temporary network configuration, you can remove or purge with command $ sudo ip addr flush enp0s Release IP address assigned by DHCP server $ sudo dhclient r 2.3. Renew IP address from DHCP server $ sudo dhclient enp0s3 ß Assume your computer get IP address on this interface Sdf 3. Wi-Fi Troubleshooting 3.1. Wireless connection troubleshooter lshw command (H/W list) $ lshw lspci command (Wireless PCI) $ lspci Ubuntu Networking Part I Page 5

6 lsusb command (Wireless USB adapter) $ lsusb 3.2. Increase Wi-Fi Signal Strength. Try this if you have Ubuntu host (not virtual machine) Install Wireless Tool $ sudo apt install wireless-tools Verify your wireless NIC info. $ ifconfig Increase Wi-Fi signal strength. $ iw reg set BO $ iwconfig wlan0 txpower 30 ß Assume you have wireless NIC wlan0 <if it doesn t work> Let try $ ifconfig wlan0 down $ iw reg set BO $ ifconfig wlan0 up $ iwconfig wlan0 channel xx ß if needed $ iwconfig wlan0 txpower 30 Ubuntu Networking Part I Page 6

7 4. Network monitoring and troubleshooting Normally, we use top program to overview all the processes or threads running in the system. However, it just the program from the old-style. We have some list of monitoring tools that works for admin as follows: 4.1. Htop Htop is essentially an enhanced version of top. It comes with visual-style and built-in commands are needed for admin Try htop $ sudo apt install htop $ htop Test htop with F1 F10 Ubuntu Networking Part I Page 7

8 4.2. Try atop, powertop, iotop, and apachetop Make your own note iftop iftop is similar to top, but it concerns only to network traffic on selected network interfaces and displays a table of current usage. You can find the answer why your Internet is very slow sometime Try iftop $ sudo apt install iftop $ sudo iftop Ubuntu Networking Part I Page 8

9 Toggle t to see what s happening? Ubuntu Networking Part I Page 9

10 4.4. nethogs Nethogs display network traffic per protocol or per subnet Try nethogs $ sudo apt install nethogs $ sudo nethogs 4.5. Try ntopng and jnettop, Make your own note. Ubuntu Networking Part I Page 10

11 4.6. Bmon Bmon monitors and helps you debug networks. You can also interact with bmon through curses or through scripting Try bmon $ sudo apt install bmon $ sudo bmon, toggle with d, l, and i to see more details on screen. Ubuntu Networking Part I Page 11

12 4.7. mtr MTR combines the functionality of traceroute and the ping tool into a single network diagnostic tool. It keep repeats every second to monitor the path between source and destination host Try mtr Normally, you don t need to install. It should come with your current Ubuntu version (16.04) $ mtr Ubuntu Networking Part I Page 12

13 Task 2: Discussion and sharing experiences Self-Study: You have to repeat all tasks in lab sheet several times to understand the solution. Write down your own report and share with your friends. Remark: Do activity by yourself. Good Luck Ubuntu Networking Part I Page 13