RE: OWA without ISA server

  • From: "adrian bolzan" <abolzan@xxxxxxxxxxxxxxxxxxxxxxxxx>
  • To: "[ExchangeList]" <exchangelist@xxxxxxxxxxxxx>
  • Date: Thu, 9 Jun 2005 09:54:29 +1000

Hi Rick,

Thanks for your reply.
I now have budgetary approval for ISA although it will still be a while
before the funds are available.
My plan would be to implement ISA as a second layer, using my packet
filetring firewall as the first line of defence, taking into accounts
recent posts on the ISAserver list that suggests that this is not
absolutely necessary.

The swiss-cheese effect is of some concern but , as you say, careful
monitoring together with patch management should alleviate most
I appreciate your comments, which give me some further food for thought.



        From: Rick Boza [mailto:rickb@xxxxxxxxxxxxxxx]
        Sent: Wednesday, 8 June 2005 11:35 AM
        To: [ExchangeList]
        Subject: [exchangelist] RE: OWA without ISA server

        To answer your original question, the scenario you paint is
inherently more risky than using some sort of proxy capability in the
        That's not to say it can't be operated securely - it can - but
it takes much more care and feeding.  You want to monitor the traffic on
all those ports you opened up, you should understand the traffic models
you expect to see across those ports, and your internal firewall is
Swiss-cheesed to support the DC and RPC communications.
        The neat thing about ISA - well there are several neat things,
but in this instance - would be the reduction in number of ports you
actually need to open up between the DMZ and your front-end server.
Exactly one, in fact, which is pretty nifty compared to what you are
using now!
        Again, it can be done and done securely and well, but an ISA
solution is much more robust.  The thing is, you need to think of the
ISA box not as a firewall in this scenario, but as an extension to your
messaging infrastructure.
        Hope that helps!

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