Sygate Forum FAQ's You probably have a DSL broadband connection that is using a DSL/NAT device or home router. DSL uses a lower MTU value than the default value of 1500 assigned by Microsoft for your network card. The best value can vary per user but for most people the MTU value of 1492 is the highest value that can be set and works for most users. When your MTU value is set higher than what is being allowed by the DSL/NAT modem an ICMP packet Type 3 is sent back to your PC telling your PC the packet that was just sent is too big, make it smaller and send it again. SPF will block this request so you must create the Advanced Rule. Now once Type 3 is allowed the Type 4 should be accepted back but just in case we set the rule to accept both ICMP type 3 and 4.
