Interesting...  Microsoft is using TCP/IP in a way that makes IE respond
faster to IIS and slower to non-IIS webservers:

http://grotto11.com/blog/?+1039831658

Could someone with IE and IIS please verify this?  A dump of TCP/IP
traffic with different versions of IE and IIS would be ideal.

Of course covered on Slashdot:

http://slashdot.org/article.pl?sid=03/01/05/2025254

This post sums things up:

 The parent +5 post is flat out wrong. This is not about persistant
 connections, which is a high-level HTTP feature that keeps a connection
 open so that the browser can send more requests. This is about a
 low-level TCP hack that IE uses to get a small speed boost on IIS
 servers, while breaking TCP standards compliance.

 If I read the article correctly, instead of creating a new TCP connection
 and then sending a request, IE sends the request immediately without
 bothering to finish the TCP handshake. Microsoft IIS web servers deal
 with it automatically, and it is faster because it saves a round-trip
 wait for the ACK and the following requset.

 The down side is that non-IIS servers have no clue what this incoming
 packet is. It must be invalid because it is not a SYN. So it gets thrown
 away, and the server might or might not reset the connection. If a
 non-IIS server resets the connection, IE goes with a standard TCP
 handshake and has wasted only the round trip time for the request packet
 and the RST. But if the server swallows the invalid packet and does not
 send a RST, then Internet Explorer will just sit around for a few seconds
 until it times out and falls back to a standard TCP conection.

 The summary is that IE is breaking the TCP protocol for a small speed
 boost when connecting to IIS servers. It results in a small speed penalty
 when connecting to most non-IIS servers. When connecting to non-IIS
 servers that do not reset the connetion, it results in a very noticable
 delay.

 It could also be a potential security risk, because if this is true, then
 it makes it very easy to IP-spoof a HTTP request against IIS (since the
 request is a self-contained packet instead of a long connection
 sequence).