adamkirchberger / mtufind

MTUFind is a tool to find the maximum transmission unit (MTU) to a destination.

mtufind

MTUFind is a tool to find the maximum transmission unit (MTU) to a destination.

What is MTU

In computer networking, the maximum transmission unit (MTU) is the size of the largest protocol data unit (PDU) that can be communicated in a single network layer transaction.

How does it work

1. Send ICMP echo request packet with a DF flag
2. Keep sending packets and increment the data size by 500 bytes each time
3. If a reply is not received then half the increment size and try again
4. Keep trying until we reach an increment of 1 byte

Install

Linux

wget https://github.com/adamkirchberger/mtufind/releases/download/v1.0.1/mtufind_v1.0.1_linux_amd64.tar.gz && \
tar xvzf mtufind_v1.0.1_linux_amd64.tar.gz && \
sudo mv mtufind /usr/local/sbin

Mac

wget https://github.com/adamkirchberger/mtufind/releases/download/v1.0.1/mtufind_v1.0.1_darwin_amd64.tar.gz && \
tar xvzf mtufind_v1.0.1_darwin_amd64.tar.gz && \
xattr -dr com.apple.quarantine mtufind && \
mv mtufind /usr/local/sbin/

Run

sudo /usr/local/sbin/mtufind github.com
MTU to 140.82.118.4 is 1500 bytes

Mac OSX

Newer Mac operating systems may complain with

"cannot be opened because the developer cannot be verified".

To fix this use the Mac install command above which resolves the Gatekeeper dialog.

Limitations

• Currently only works for IPv4 destinations
• Needs root access as the standard ICMP libraries do not support DF flag