Outlook2003: why does RPC over HTTP need so many open ports?

[I. Thamdrup]

Hi, fellow Outlook users,

I'm using Outlook 2003 on Windows XP SP2 and I'm trying to connect to
an Exchange mailbox using OWA. As far as instructions in MS TechNet and
MSDN are concerned, I should only need to open one port in the client
machine, that is, TCP 80 or 443. I understand that after that, Outlook
should channel ALL its traffic through that port, right?

So I followed the "Configuring Outlook 2003 for RPC Over HTTP" article
(http://office.microsoft.com/en-us/assistance/HA011402731033.aspx)
word-by-word to set up an account in Outlook, opened port 80 ... and
yet I couldn't log in; the "Connecting to (someserver)" dialog refused
to accept my username and password.

A brief look with the TCPView utility showed that Outlook tried to
connect not only to port 80, but also to 135 (RPC) and several random
ports in the high (1024+) port range. However, I absolutely cannot open
any other ports than 80 or 443 in the client machine, so either I can
somehow trick Outlook into using nothing but those ports, or .. well,
fail miserably and make several people unhappy.

What I'm hoping for, if you'd be so kind, is that you could explain to
me whether I got it all wrong and Outlook in OWA mode must still have
access to as many outgoing ports as it pleases, or is there a way to
persuade it into using only 80 and/or 443.

Thank you for your time, I'll be grateful for your answers.

 

[neo [mvp outlook]]

If you are defining a corporate firewall rule, it would look something like
this for OWA and RPC/HTTPS.

SOURCE -> CORPORATE SERVER
<any> -> 443


SOURCE in this case is any machine on the Internet can access the server on
port 443 (HTTPS)


For a desktop firewall that is stateful (means it monitors both outbound and
inbound), then the rule would look something like....

WORKSTATION -> CORPORATE SERVER
<any> -> 443

The reason for this is that every workstation can open an arbitrary port in
the ephemeral port range (1024 through 4999).

/neo

PS - When Outlook 2003 can't connect via TCPIP or HTTP, it fails over to the
other protocol. This is why you see the RPC port of 135. RPC is not needed
to support RPC/HTTPS.