How does one verify if there is an MTU issue preventing Enhanced compression or acceleration from working?

Products

• PacketShaper

Issue/Introduction

This is usually not a problem, but if for some reason the default setting for auto MTU is not working one could probe the network with tunnel ping to verify the largest size tunnel packet which is allowed through the network.  Tunnel ping sends and receives IP protocol 99 packets between Xpress IP addresses of partner PacketShapers.  In this example we can see that a 1470 byte tunnel ping is successful yet a 1471 byte tunnel ping fails. The target IP address is the Xpress IP address of the tunnel partner. 

usage: tunnel ping <tunnel>|{<device> <target ip-address>} [<pingsize> <count>]

PacketShaper# tunnel ping main 10.1.2.2 1470 3

1470 bytes from 10.1.2.2, seq=0, time=2 ms
1470 bytes from 10.1.2.2, seq=1, time=2 ms
1470 bytes from 10.1.2.2, seq=2, time=2 ms

--- 10.1.2.2 tunnel ping statistics ---

3 packets transmitted, 3 packets received, 0% packet loss

PacketShaper# tunnel ping main 10.1.2.2 1471 3


---10.1.2.2 tunnel ping statistics ---

3 packets transmitted, 0 packets received, 100% packet loss

 

Through the WUI or from the Cli the Tunnel MTU setting could be set to 1470

since that is the largest size tunnel ping which was successful.

 

PacketShaper# tunnel mtu 1470

MTU has been set to 1470.