Guys I have had this question come up regarding the network but have not idea what it could be, is MTU a setting on the ADSL router or is it some we need to change on the PIX firewall. Not got a clue what this is.
As discussed, pMTU (Maximum Transmission Unit) is required to find the optimum packet size across a WAN network. In order for pMTU to work correctly, ICMP type 3 code 4 needs to be enabled on the client side. Not having the MTU sized correctly can significantly slow down the performance of the system.
e.g. If we send a packet size of 1500 and the clients MTU size is 500; when the packet reaches the clients end it would need to be fragmented into 3 packets of 500. This can increase the latency on the network and therefore produce poor performance.