The ping packet size in Microsoft Windows is a maximum 65500 bytes However, the default setting for the buffer size of Cisco routers is 18024 bytes maximum size (use show buffers). Because of this, you will sometimes get a timeout message from Windows. To correct this, use the command buffer huge size 65500. Then you can use every size packet from Windows to test pings.
An important Caution before you change buffer size
You might want to check to make sure doing so won’t cause the router to run out of I/O memory. This situation is unlikely unless
the router’s Huge buffers have been tuned and the number of permanent buffers is increased, but it’s a good idea to check routers IO memory before you actually change the buffer size.