How to Ping a Fragment MTU in Linux
- 1). Log in to the Linux computer.
- 2). Start a command shell, either by logging in in text mode, or by clicking on the "Terminal" icon on the graphical desktop.
- 3). Type the following command into the shell to find out the current MTU for your network interface:
ifconfig eth0
Replace "eth0" by the Linux name of the network interface in question, then press "Enter." Make a note of the interface's current MTU (in bytes), listed after the "MTU" heading in the fourth line of the output of "ifconfig." - 4). Determine the MTU for the path to a remote host by pinging the host with your local MTU from Step three, by typing the following command into the shell:
ping -s 1500 sunburn.stanford.edu
Replace "1500" by the local MTU from Step three, and "sunburn.stanford.edu" by the remote host you want to ping, then press "Enter." Make a note of the size of the packets received from the remote host by "ping". You can find that number at the beginning of each line that reads "bytes from sunburn.stanford.edu" in the output of "ping." That number is the MTU (in bytes) for the current path between your network interface and the remote host. - 5). Ping the remote host with a packet size equal to a fragment of your local MTU, by typing the following command into the shell:
ping -s 520 sunburn.stanford.edu
Replace "520" by the path MTU as obtained in Step four, then press "Enter." Since you are using a packet size no larger than the path MTU, the packets received back by "ping" will have not been fragmented any further.
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