Useful Network Connectivity Tool

Off the back of my previous Windows Server Developer Preview problem I also came across the Microsoft Internet Connectivity Evaluation Tool. Quite useful for determining the NAT capability, ECN capability, TCP throughput, UPnP capability and multiple connection capability of your router.

Windows Server 8 Developer Preview - Networking Problem

So I fired up a copy on a spare whitebox only to find HTTP and SMB outbound traffic timing out. Bizarrely ping and traceroute were working, so ICMP and UDP were working, as was inbound SMB connections – just not outbound. Did the usual tricks – upgrade network drivers, disabled NIC-based offloading and modified the usual suspects via netsh (Task Offload, Chimney Offload, RWIN tuning) to no avail.

It this point I compared the ‘netsh int tcp show global’ and ‘netsh int ip show global’ outputs with the defaults from a Windows Server 2008 R2 box and noticed that ‘ECN Capability’ in the TCP Global Parameters for Windows Server 8 Developer Preview was Enabled. I set this to disabled using:

netsh int tcp set global ecn=disabled

and outbound connectivity was established.