As shown above, on the AR1 G0/0/0 mouth MTU to 800, the command for MTU 800,

To ping ping now the same network segment, such as PC AR1 or AR1 to ping AR2, can normal shard,
But the PC to ping AR2, specific for ping 2.2.2.3 - l 2000, will display caught on the wrong, AR2 did not return package