How To Know Your ISP's MTU

I found this procedure somewhere, just can't remember when and where. I thought it would be very beneficial to repost it so here it is.

"The "MaxMTU" value you should use in the Windows Registry is actually limited by your ISP's MTU value, since all packets will be traveling through their servers.
To determine the MTU of your ISP, try the following:

In Dos Prompt(Command Prompt), type:
ping -f -l [packetsize] [] where [packetsize] is the amount of data you want to send ( between 0 and 1500 bytes ) and [] is your ISP's URL (you can also use your gateway, or any server your connection always passes through instead of your ISP's URL)."

For example: ping -f -l 100

"The largest value that does not give you the error "Packet needs to be fragmented, but DF set" will be your ISP's MTU, for example: 28, (excluding the IP [20 bytes] and ICMP [8 bytes] headers). Use the following table to interpret the number you received and determine your ISPs MTU:

Largest non-fragmented value Your ISPs MTU What you should use
1472 1500 use 1500 (1472+28=1500) - Ethernet
1468 1496 1496 - the Ethernet standards actually call for using 1496, although 1500 is most often used for simplicity
1464 1492 1492, the Largest PPPoE MTU
1452 1480 1480, Windows XP PPPoE MTU
548 576 (or higher) Check your Registry settings, your MTU might be the limiting factor if set to a small number."