How to discover the MTU?

[huangzhy]

The extended ping command with sweep range of sizes option allows you to vary the sizes of the echo packets being sent. This capability is useful for determining the minimum sizes of the MTUs configured on the nodes along the path to the destination address.How can this command discover the MTU along a path to a destination?

[thisisshanky]

If you send a ping packet with a size = 500 bytes, and along the way to destination, any router has an MTU size say 400 bytes....and if you set the Dont Fragement bit of the packet, the router cannot send the packet, without fragmenting it. So it will drop the packet and sent an ICMP message to the host. This way you can find out the MTU along the path.