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

From: "Greg Mulholland" <gmulholland@xxxxxxxxxxxx>
To: <isapros@xxxxxxxxxxxxx>
Date: Mon, 15 Jan 2007 09:22:23 +1100

Re: [isapros] Re: ISA, Exchange 2007 and Perimeter Networkswhats gets me is
that there is "stuff all" documentation i have been able to find on CAS
scenario's from the exchange team. other than "oh please put it in the lan, not
supported in the dmz". Time to clear some stuff up i think.
----- Original Message -----
From: Thomas W Shinder
To: isapros@xxxxxxxxxxxxx
Sent: Saturday, January 13, 2007 4:10 AM
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

Jason,

Excellent idea. Makes sense to put the Internet facing CAS in a separate zone
from the non-Internet facing CAS. I don't see any problems putting the
auth-access DMZ addresses in the site, and they probably already are :)

Thomas W Shinder, M.D.
Site: www.isaserver.org
Blog: http://blogs.isaserver.org/shinder/
Book: http://tinyurl.com/3xqb7
MVP -- Microsoft Firewalls (ISA)

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From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
Behalf Of Jason Jones
Sent: Friday, January 12, 2007 5:53 AM
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

Either way, I think the idea of an intranet CAS and extranet CAS is
probably a good approach - the extranet CAS one would assume could then go into
the auth access perimeter network whilst the intranet one could stay on the
LAN. In this model, each CAS has a different security risk and hence could be
put into different security zones.

Would it be such a bad thing to add the perimeter subnet to the AD site? It
will have domain members in it after all...
Jason Jones | Silversands Limited | Desk: +44 (0)1202 360489 | Mobile: +44
(0)7971 500312 | Fax: +44 (0)1202 360900 | Email: jason.jones@xxxxxxxxxxxxxxxxx

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From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx] On
Behalf Of Greg Mulholland
Sent: 12 January 2007 05:35
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: ISA, Exchange 2007 and Perimeter Networks

doing 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: