IExplorer 5/6 closes NTLM authenticated connection after downloading page

[Gareth Bowen]

Hi

I am working on a product that contains a simple HTTP server. This
server provides HTML pages so that a user can control the application
using a normal web browser. NTML is used to authenticate the
connections. The machines are on the same network and there is no
proxy involved at all.

I am having no issues at all with the authentication process itself.
The connection remains active during the three way handshake and the
authentication succeeds. I am also using the connection keep-alive
header in all of my responses. IE is also including the connection
keep-alive headers. However, once it has finished downloading the HTML
content, IE closes the connection. When the user presses refresh, it
creates a new connection, re-authenticates using the same credentials,
gets the page and closes again. Whilst the user is not prompted for
login details on each refresh, it seems a bit OTT to have to
reauthenticate each time.

If I disable NTLM on the server, IE keeps the connection alive.
If I enable NTLM and use Netscape 7.1, the authentication succeeds and
the connection stays alive.

I have tried various combinations of HTTP1.0 and 1.1 requests with the
appropriate Connection: Keep-Alive or Close headers. Netscape always
does exactly as the instruction says ... IE does without NTLM, but
with the authentication, it always closes the connection.

Therefore, I'm wondering why IE is behaving like this. With NTLM
disabled, there is no difference between the HTTP headers (other than
WWW-authenticateand the HTML pages are identical. It would seem that
there is logic in IE that ignores connection persistence where NTLM is
used. Is there a reason why IE closes the connection but Netscape does
not? Can this behaviour be changed?

I have found various things on the web which talk about the connection
closing during the authentication (I tried closing after replying with
the initial 401 authorisation required message as mentioned on certain
sites) but haven't found anything where the connection closes
afterwards. I also found something indicating that a page less than
1460 bytes would result in closure - but providing a larger page
didn't change a thing. This behaviour is seen even with a page that
simply displays "Hello world".

With no luck from searching the web, someone suggested that I try
groups - I've not used them before so I apologise if this issue has
come up before! I did search beforehand but had no luck.

Thanks in advance

Gareth Bowen