Finally the problem was on the server . A misconfigured registry was disabling the Path MTU Discovery , forcing the packet size to 536
for all non-local destination IP addresses.
Note: The modification of the Windows NT TCP/IP parameters involves editing the registry. This should only be attempted by experienced system administrators because mistakes can render the system unbootable. After these registry changes are done, reboot to apply the changes.
PMTU discovery is enabled by default, but can be controlled with the addition of this value to the registry:
A "1" enables discovery while a "0" disables it. When PMTU discovery is disabled, a MTU of 576 bytes is used for all non-local destination IP addresses. The TCP MSS= 536.
When you set this parameter to 1 (True), it causes TCP to attempt to discover the Maximum Transmission Unit (MTU or largest packet size) over the path to a remote host. With the discovery of the Path MTU and the limitation of TCP segments to this size, TCP can eliminate fragmentation at routers along the path that connect networks with different MTUs. Fragmentation adversely affects TCP throughput and network congestion.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...