RE: External Network Logic

  • From: "Thor \(Hammer of God\)" <thor@xxxxxxxxxxxxxxx>
  • To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
  • Date: Wed, 7 Dec 2005 17:25:37 -0800

Internal network PC's go out a different ISA server altogether for Internet via a business class high speed cable circuit I have specifically for client Internet access. It's a 6 meg circuit that supports around 80 of my people, and is working well. I don't commingle my business services in the DMZ with outbound net access. That would be silly ;) The "client-server" ISA will not affect Internet access.

t


----- Original Message ----- From: "Amy Babinchak" <amy@xxxxxxxxxxxxxxxxxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Wednesday, December 07, 2005 5:07 PM
Subject: [isalist] RE: External Network Logic



http://www.ISAserver.org

How many hops does that make to the Internet for the Internal network
PC's?

Amy

Harbor Computer Services
Small Business Computer Specialists

Client Blog: http://smalltechnotes.blogspot.com/
Tech Blog: http://isainsbs.blogspot.com/
Website: http://www.harborcomputerservices.net/




-----Original Message----- From: Thor (Hammer of God) [mailto:thor@xxxxxxxxxxxxxxx] Sent: Wednesday, December 07, 2005 8:06 PM To: [ISAserver.org Discussion List] Subject: [isalist] RE: External Network Logic

http://www.ISAserver.org

OK- just so we're on the same page-- I'm not talking about my
back-to-back
DMZ config that does indeed have a DMZ Perimeter network on the BE ISA
for
my FE Exchange server.  That's done.

I'm not talking about a NEW box going into my internal network to
physically
separate client systems from server systems.  That's the one I was
talking
about having 2 nics with no "External" resources.
t



----- Original Message ----- From: "Thor (Hammer of God)" <thor@xxxxxxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Wednesday, December 07, 2005 4:41 PM
Subject: [isalist] RE: External Network Logic



http://www.ISAserver.org

This isn't a back-to-back config.  This is a single server going in
between my clients and my servers... There won't be a way to "NAT to
the
Internet" in that config as the only defined rule will be a route
relationship from the Perimeter to the Internal.

I understand the concept that "Internet" is is the default gateway,
but in
this case, there can't be a "Nat" relationship anywhere.
t


----- Original Message ----- From: "Thomas W Shinder" <tshinder@xxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Wednesday, December 07, 2005 4:25 PM
Subject: [isalist] RE: External Network Logic



http://www.ISAserver.org

No, the Internet is always there, unless you're talking about a
caponized ISA firewall (single NIC).

The Internet is reached via the NIC with the default gateway defined
on
it, which in a back to back config would be the internal interface of
the FE ISA firewall.

There is one point of confusion induced by the UI -- and that's the
ability to create an "external Network".  There is no difference from
the firewall's point of view between a perimeter Network and an
external
Network. So, you can create another external Network if you like, but
its *exactly the same* as a perimeter network from ISA's
multinetworking
point of view. The default External Network is always there (except
for
the unihomed ISA firewall).

For example, if a client on the default Internal Network connects to a
host on the perimeter network between the ISA firewalls, the
connections
are routed and the source IP address is not replaced. If a host on the
default internal Network connects to an IP addresses that is part of
the
default External Network (which is the Internet) the connection will
be
NATed.

The ISA firewall's ability to enable control over your route
relationships really does give you a lot of flexibility.

Thomas W Shinder, M.D.
Site: www.isaserver.org
Blog: http://spaces.msn.com/members/drisa/
Book: http://tinyurl.com/3xqb7
MVP -- ISA Firewalls



-----Original Message-----
From: Thor (Hammer of God) [mailto:thor@xxxxxxxxxxxxxxx]
Sent: Wednesday, December 07, 2005 5:39 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: External Network Logic

http://www.ISAserver.org

One thing though, just so I understand-- How would I NAT to
the Internet?
There *is no* "Internet" per se in a 2 NIC config with both
defined as ISA
Firewall Networks, right?  There would be route relationship from the
Internal to the DMZ Perimeter.  The Internet would only exist if an
Interface was added and not defined elsewhere, correct?
t

----- Original Message ----- From: "Thomas W Shinder" <tshinder@xxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Wednesday, December 07, 2005 3:01 PM
Subject: [isalist] RE: External Network Logic



http://www.ISAserver.org

The default External Network is defined as all addresses that
defined by
any other ISA firewall Network. So, there is still an
external network,
you just don't have any access to it, since you've created
ISA firewall
Networks for both the NIC (one for the default Internal
Network and one
for the ISA firewall Network representing the perimeter network NIC).

You can use this in a number of scenarios, like turning the
DMZ between
the BE and FE ISA firewall into an ISA firewall Network and creating
a
route Network Rule between that and the default Internal Network, but
still NAT'ing to the Internet. Pretty slick, eh?

Thomas W Shinder, M.D.
Site: www.isaserver.org
Blog: http://spaces.msn.com/members/drisa/
Book: http://tinyurl.com/3xqb7
MVP -- ISA Firewalls
**Who is John Galt?**



> -----Original Message-----
> From: Thor (Hammer of God) [mailto:thor@xxxxxxxxxxxxxxx]
> Sent: Wednesday, December 07, 2005 4:57 PM
> To: [ISAserver.org Discussion List]
> Subject: [isalist] External Network Logic
>
> http://www.ISAserver.org
>
> So, you've got ISA with 2 NIC's.  You define the Internal
> range on one NIC,
> leaving the other NIC as "External."  You then add a
> perimeter network, and
> give it the IP range of what used to be the "External" NIC.
> What happens to
> the concept of the External network since you now have a
> trusted Internal
> network and a less trusted "Perimeter" network, but no real
> "External"
> network anymore.  Will it just be an "empty" network set
> sitting there all
> alone in the cold, cold ground?
>
> t
>
>
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