[isapros] Re: ISA, Exchange 2007 and Perimeter Networks

From: "Greg Mulholland" <gmulholland@xxxxxxxxxxxx>
To: <isapros@xxxxxxxxxxxxx>
Date: Fri, 12 Jan 2007 16:34:51 +1100

Re: [isapros] Re: ISA, Exchange 2007 and Perimeter Networksdoing a little bit
more reading the only thing i can think might be the reason is that apparently
each mailbox server needs to have a CAS server in its AD site. Therefore they
recommend you keep the cas box on the same lan. Also in multi domain
environments this would add more design considerations. Also in larger
environments you might need 2 CAS boxes, one for internal users and one for
external users, for the sake of keeping outbound lan access out of the dmz or
better design.

but im not sure about the whole idea of the "swiss cheese" argument. seems a
bit like flogging a dead horse to me..i dont see how or why it wouldn't work in
the dmz environment.

greg

----- Original Message -----
From: Thomas W Shinder
To: isapros@xxxxxxxxxxxxx
Sent: Friday, January 12, 2007 3:22 PM
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

WORD!

I'll gladly joining you in that public nut-kicking when the time comes. What
I want to understand first is what are the protocol requirements for the CAS to
the back-end components, and what their rationale is for making the statements
that have been reported so far. They might have a good point, and if they have
it, I want to hear it. But if the point is 'it's too hard" or "I don't
understand network security, I just say what my boss tells me to say" or "I'm
on the take with Syphco" then those aren't valid and body parts will deserve
some shaking up in the public square. The least they can do is state "we don't
have the time or inclination to show you have to provide the highest level of
network security, but it is possible to do it right, we're just not going to
show you how to do it" as a disclaimer. With that, we can then go ahead and
help those who want to be helped J

From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
Behalf Of Thor (Hammer of God)
Sent: Thursday, January 11, 2007 6:40 PM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

It may be just this type of "beating it to death" that is required to get the
Exchange group's attention. I don't really care if they don't support
"perimeter network" deployments as long as ISA is an exception. I have every
intention to ensure that an ISA authenticated perimeter network DMZ segment "in
front" of the CAS server is fully supported if the proper protocols are
allowed. I will make sure to press them into officially stating why it is not
supported. Even so, if they try that, I will publicly kick them in the nuts.

On 1/11/07 4:15 PM, "Jason Jones" <Jason.Jones@xxxxxxxxxxxxxxxxx> spoketh to
all:

Hi Amy,

I am not really sure for their reasoning, but think it is based around the
"Swiss cheese", don't pass intradomain traffic across a normal firewall
argument.

Sorry, my bad for using the term DMZ, the exact phrase used by Scholl is
"It's true. The Client Access Server (CAS), which among other things includes
the OWA feature, is not supported in a perimeter network (aka a DMZ). Instead
you'll deploy one or more CASs inside your organization and put a robust
firewall such as ISA 2006 in front of it." I am guessing from experience of
other Exchange team recommendations that when they say perimeter network they
really mean a traditional DMZ which is created using traditional packet filter
firewalls. The recommended deployment is to put the CAS on the internal network
e.g. on the same network as the Exchange back-end servers. Once the CAS is on
the internal network, it should then be published to the Internet using ISA.

This design if fine if you want a simple open network where all servers exist
in the same security zone and hence all trust each other, but many people are
now trying to better this design by placing different types of servers into
different security zones based upon their risk level and internet presence -
say hello to the ISA auth access perimeter network! ;-)

Basically I think it all harks back to the "don't put domain members in a
DMZ" mantra which is a pretty fair statement when using PF firewalls like PIX,
but things have moved on as least privilege authenticated access perimeter
networks with ISA are now getting advanced enough to challenge this argument.
Maybe the difference between a PIX firewall and ISA firewall is just too subtle
for some people???

Think we have now done this to death now!! - be very surprised if the
Exchange team go back on these type of statements though. I remember Tom
banging his head against a brick wall with Henrik based upon one of his
MSExchange.org articles which said "not in the DMZ" type statements.

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From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
Behalf Of Amy Babinchak
Sent: 11 January 2007 23:15
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

Jason,

What's the reasoning behind CAS not in the DMZ? Where to they want it?
Handing nude off the router? Behind a firewall?

If the later, then just drop the out dated DMZ language. Most firewall admins
think that DMZ means nude off the other port on my nat box. Your least priv
design puts CAS safely behind a firewall.

Amy Babinchak
Harbor Computer Services

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From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
Behalf Of Jason Jones
Sent: Thursday, January 11, 2007 5:58 PM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

Thanks Amy - maybe I am being a little oversensitive, just didn't expect some
of the initial responses.

I tend to avoid most of the main mailing lists, probably for similar reasons
as others, and I tend to hang out at isaserver.org 95% of the time. Hence maybe
why only Tom (and Stefan) tend to see my input and views on stuff.

Tom invited me to this list as he felt it would be a good place for me to
pose all the questions that he can't answer or go unreplied on isaserver.org

I really do value the combined "ISA brain power" here, but just think it
could be a little more forgiving and friendly at times...having said that I
have found answers here that I just couldn't get elsewhere, so don't
misunderstand me as ungrateful.

Anyhow back to the "core issue", from what I hearing from Exchange MVP
contacts, MS are playing the "CAS in a DMZ is totally unsupported" tune very
strongly. This is a real shame as it looks like I will never be able to deploy
the existing least privilege design with Exchange 2007 without fear of
customers coming back to us after trying to log PSS calls or getting other
non-ISA firewall guys in who slate the design...oh well, at least ISA will
still involved to some degree, just not as cool as it could be...

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From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
Behalf Of Amy Babinchak
Sent: 11 January 2007 15:09
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
Jason don't get discouraged. The changes in Exchange are monumental so there
are bound to be disagreements and changes of opinion on how to best secure it.
The concept of an authenticated access DMZ in a separate security zone allowing
only a very minimal set of protocols is a completely foreign concept to 99% of
firewall admins out there. That fact you are even thinking about this stuff put
you in an elite class. The rest are still poking holes and setting up VLANs.

Tom, Thor and Jim can be a bit clubby and a little overly poky to new comers.
It's a twitch they developed after participating on the ISA server mailing
list. It got worse when they decided to join a general purpose SBS list. I'm
not sure that they'll ever completely recover.

Amy

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From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
Behalf Of Jason Jones
Sent: Thursday, January 11, 2007 5:47 AM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

Wish I had never asked now...sometimes, some of you guys really don't make it
easy for new people to try express their views and pose questions for comment
without being slapped down. One minute I am being labelled as an "idiot" for my
comments/views, the next minute someone else who says the same thing as me is
now right and not challenged. What gives?

I know many of you guys don't know me from Adam, but kinda unfair to just
assume I know jack about ISA and secure network design just because I'm not
"part of the club".

Anyhow, thanks to Tim and Tom for seeming to share my disappointment with the
decision made by the Exchange 2007 team...I think I need to try and find out
how "official" their lack of support with 2k7 is going to be before I can
continue recommending the least privilege model I have been using for Exchange
2003.

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From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
Behalf Of Jim Harrison
Sent: 11 January 2007 04:30
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
..maybe I'm just tired.
I spent two hours trying to get home tonight and I'm clearly not in my mind
(right or otherwise).
Forget I wrote and we'll start over tomorrow.

From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
Behalf Of Thor (Hammer of God)
Sent: Wednesday, January 10, 2007 8:18 PM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

That's exactly what I'm talking about. And precisely the configuration I
deploy:

My FE is in the authenticated segment of the DMZ - and a member of my
internal domain; however, the "recommended protocols" the Exchange group
recommends are not necessary- and thus, Steve's contention that "CIFS and all
that other stuff... Might as well just be internal" I reject. I only allow
Kerberos-Sec, LDAP, LDAP GC, Ping and DNS only from my FE to the internal DC's.
And only HTTP to the BE's.

Even if the other prots WERE required, it would still be far smarter to
deploy the FE in the authenticated DMZ with limited access than to just give
full stack access to the ENTIRE internal network. This is a deployment of a
services made available (initially) to a global, anonymous, untrusted network.

Maybe I'm not properly articulating my point, but I have to say I'm really
surprised that we are having this conversation...

On 1/10/07 7:10 PM, "Jim Harrison" <Jim@xxxxxxxxxxxx> spoketh to all:
C'mon, Tim; I know what your deployment recommendations are; this isn't it.
He wants to extend his domain via "remote membership"; not create a separate
domain.

From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
<mailto:isapros-bounce@xxxxxxxxxxxxx%5d> On Behalf Of Thor (Hammer of God)
Sent: Wednesday, January 10, 2007 4:26 PM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

Because it's safer that way, that's why... That's what an authenticated
access DMZ perimeter is for- with a CAS server that presents logon services to
any Internet user, I would (and, in fact, require) that the server be in a
least-privileged authenticated access perimeter network that limits that
servers communications to the minimum required for required functionality - and
only to the hosts it needs to talk to.

Let's say there is a front-end implementation issue or coding vulnerability:
the CAS on the internal network would allow unfettered, full-stack access to
the internal network. A CAS in a perimeter DMZ would mitigate potential
exposure in the event of a 0day or configuration issue.

"Safer on the internal network" is a complete misnomer when it comes to
servers presenting services to an untrusted network.

On 1/10/07 3:04 PM, "Jim Harrison" <Jim@xxxxxxxxxxxx> spoketh to all:
Why would you want to place a member of your internal domain in your DMZ, fer
chrissakes?!?
Hosting any domain member in the DMZ is a difficult proposition; especially
where NAT is the order of the day.
You can either use a network shotgun at your firewall or attempt to use your
facvorite VPN tunnel across the firewall to the domain.

Jim

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From: isapros-bounce@xxxxxxxxxxxxx on behalf of Jason Jones
Sent: Wed 1/10/2007 2:35 PM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

From what I can gather, the new CAS role now uses RPC to communicate with the
back-end (not sure of new name!) servers so I am guessing that this is an "RPC
isn't safe across firewalls" type stance. Which I guess for a PIX, is a pretty
true statement.

Just think how much safer the world will be when firewalls can understand
dynamic protocols like RPC...maybe one day firewalls will even be able to
understand and filter based upon RPC interface...maybe one day... :-D ;-)

Shame the Exchange team can't see how much ISA changes the traditional
approach to DMZ thinking...kinda makes you think that both teams work for a
different company :-(
Jason Jones | Silversands Limited | Desk: +44 (0)1202 360489 | Mobile: +44
(0)7971 500312 | Fax: +44 (0)1202 360900 | Email: jason.jones@xxxxxxxxxxxxxxxxx
<mailto:jason.jones@xxxxxxxxxxxxxxxxx>

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From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
<mailto:isapros-bounce@xxxxxxxxxxxxx%5d> On Behalf Of Greg Mulholland
Sent: 10 January 2007 22:07
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

I seriously hope that they have take different paths and these are not
limitations on the software or it is going to mean a nice little redesign and
break from custom..

Greg
----- Original Message -----
From: Jason Jones <mailto:Jason.Jones@xxxxxxxxxxxxxxxxx>
To: isapros@xxxxxxxxxxxxx
Sent: Thursday, January 11, 2007 8:25 AM
Subject: [isapros] ISA, Exchange 2007 and Perimeter Networks

Hi All,

I heard today from an Exchange MVP colleague that members of the Exchange
team (Scott Schnoll) are saying that they (Microsoft) do not support placing
the new Exchange 2007 Client Access Server (like the old Exch2k3 FE role) role
into a perimeter network. Has anyone else heard the same? This sounds very
similar to Exchange admins of old when they didn't really understand modern
application firewalls like ISA could do - RPC filter anyone???
http://groups.google.co.uk/group/microsoft.public.exchange.design/browse_thread/thread/4ecab9cb8e50015e/4db165c21599cf9b?lnk=st&q=cas+dmz+isa&rnum=2&hl=en#4db165c21599cf9b

<http://groups.google.co.uk/group/microsoft.public.exchange.design/browse_thread/thread/4ecab9cb8e50015e/4db165c21599cf9b?lnk=st&amp;q=cas+dmz+isa&amp;rnum=2&amp;hl=en#4db165c21599cf9b>

I have just about managed to convince Exchange colleagues (and customers) of
the value of placing Exchange FE servers in a separate security zone from BE
servers, DC's etc and now I here this.

Are the Exchange team confusing the old traditional DMZ's with what ISA can
achieve with perimeter networks?

From what I believe, it is good perimeter security practice to place servers
which are Internet accessible into different security zones than servers that
are purely internal. Therefore, the idea of placing Exchange 2003 FE servers in
an ISA auth access perimeter network with Exchange 2003 BE servers on the
internal network has always seemed like a good approach. It also follows a good
least privilege model.

Is this another example of the Exchange and ISA teams following different
paths????

Please tell me that I am wrong and that I am not going to have to start
putting all Exchange roles, irrespective of security risk, on the same network
again!!!!

Comments?

Cheers

All mail to and from this domain is GFI-scanned.

References:
- [isapros] Re: ISA, Exchange 2007 and Perimeter Networks
  - From: Thomas W Shinder

[isapros] Re: ISA, Exchange 2007 and Perimeter Networks

Other related posts: