Living with ISA 2006 and the ISA Firewall client


One of my big projects in 2008 was making the transition from my old firewall to a new solution.  I’ve had 18 months or so to work with ISA and the workstations running the Firewall Client software, and thought I’d share my experiences.

First, a little background.  The network I inherited long ago was protected by a Watchguard Firewall.  At the time, it was a moderately capable stateful packet inspection (SPI) unit that performed what was asked of it;  ingress filtering with a little protection from a few application layer proxies.  But times had changed and communication sessions had become more sophisticated.  Exploits were getting more creative and difficult to defend against because they were occurring high up at the application layer.  Like many SPI firewalls, it’s ability to intelligently control outbound traffic was limited.

My acceptance criteria included better protection at the application layer, as well as close integration with my Active Directory based infrastructure.  I also needed a firewall that would help me get a handle on outbound traffic.  ISA 2006 was the answer.  I chose a Celestix MsA4000i appliance running ISA to simplify the hardware procurement and deployment process.

During my implementation planning, I had the opportunity to talk at length with Richard Hicks, a Senior Engineer for Celestix Networks.  Celestix makes a fine product line of security solution appliances running ISA, and Richard (a recent MVP award winner) had excellent insight into ISA implementations, large and small.  I give him credit for helping me translate the functional requirements I was used to with my old firewall, while giving practical recommendations on how ISA performs those same functions, and policy design and implementation.

One of the unique traits of ISA is the various methods it allows internal clients to communicate with. 

  • SecureNAT.  The most basic of the three, and uses ISA as the gateway/router for traditional perimeter based protection.  Used when a default gateway is assigned to the client.
  • Web Proxy Client.  Generally called upon when there are web based requests such as HTTP and FTP calls, etc. 
  • Firewall client.  An optional piece of the ISA solution that runs on Windows clients, and extends the functionality of ISA in ways that cannot be matched by other solutions.

None of these are mutually exclusive, and can be run all at the same time.  Unfortunately, this flexibility can hinder your intentions.  If you want to restrict outbound communication to authenticated access only, running SecureNAT will compromise that ability.  The solution?  Run all non server systems without a default gateway, to force the client to use the web proxy client, or firewall client.  In the event that the target is beyond your LAN, the firewall client will handle all routing.

The easiest transition would have been using SecureNAT for the initial deployment, but there was an opportunity for monumental improvements if I attempted to go without it.  Am I glad I took this extra step?  Yes!  Some of the highlights have been:

  • Outbound connections limited to authenticated users only.  If an outbound connection is made,  I could see what user is requesting it.  Logging provides meaningful data now.
  • True egress control.  Connections initiated from the inside can finally be controlled.  Once everything was up and running, it was fascinating to see what was initiating outbound connections.
  • Forces compliance of application related restrictions.  IM and P2P applications specialize in working their way around firewalls.  The combination of the web proxy, and the firewall client with no SecureNAT helps achieve this.
  • Suppression of malware.   The combination of allowing only authenticated outbound access, along with utilizing an automated malware blacklist database helped control users who had a knack of making a mess out of their PCs.

The results of the improved security stance was impressive.  So was the amount of complaining from end users.  They were furious.  I had angry developers shutting off the firewall client software on their PC.  It made them feel good until they realized shutting down the firewall client gave them less access, not more.  They made claims that BitTorrent was a necessary part of their job, and found it insulting that outbound SSH sessions were not allowed to any host on the Internet.  They didn’t like that their non-domain joined test machines (or unapproved personal laptop) would require a username and password before they could access the Internet.  Their complaints went straight to the top of the organization, as did my explanations.  Security won out, and policies stood without change.

There were some hiccups along the way.  Most deployment related problems were fixed, while others forced some changes in how we worked.  The ISA community is an active one, but with the move of using workstations running the ISA firewall client without a default gateway, it made finding out answers much more difficult.  Some of the obstacles I ran into were:

  • Lack of support for CIFS traversing across network segments.  The firewall client cannot handle this alone, and needs a default gateway.
  • Vista and later workstations need a static route added for remote targets that were not web based.  This can be added via DHCP (option 121, but don’t try to add it via the DHCP snap-in in Vista, otherwise it won’t work).  Thanks to some assistance from Richard Hicks and Microsoft for ultimately explaining the reason behind the inconsistent behavior between XP and Vista.  More info can be found here: 
  • Building up a healthy list of domains that will be allowed to have anonymous outbound access.  OS and application update domains and mirrors are good examples of this.
  • Older Outlook Clients (2003) wouldn’t talk to the internal Exchange Server using it’s MAPI connection until the following tweak was made:
  • Web services that use SSL, but do not run over port 443 had to be accommodated for.
  • Browser proxy configurations in *nix workstations may not be enough.  For those workstations, leave a default gateway.

As you can see from the links I provide, I found invaluable during my implementation.  It attracts some of the brightest and the best in the security world who contribute articles, and to community forums.  It’s a great resource for any ISA administrator. 

My biggest annoyances in using the firewall client are small, but still worth mentioning.

  • The virtual black hole that the occurs on socket of the workstation running the firewall client.  Trying to debug via traditional methods is nearly impossible.  It simplifies the number of connections from the client, but it’s hard to tell the contents of the connection.
  • The name.  “Firewall Client” implies that it is some application that protects a workstation like ZoneAlarm, Norton, or the Windows Firewall.  A simple name change would eliminate this confusion to newer users, and some IT guys not familiar with ISA.

If I were to do it over again, I would have given more notice on what changes would be occurring, and why.  I had previous verbal green lights from management to restrict thing things like P2P and IM sessions, and our written IT policies had already reflected these restrictions.  I just never had the capability to do so.  I warned staff, but apparently not enough.  I had to do a healthy amount of explaining, which was fine because I had the technical reasons, and the business case on my side. 

I look forward to the next version of ISA (Threat Management Gateway, or TMG) and the steps it takes to improve upon the Firewall Client component.  Recommended reading on using the Firewall Client in ISA 2004 and 2006 can be found below.

Firewall Client

Database of malware domains that can be imported directly into ISA

A special thanks to Richard Hicks from Celestix, and my good friend Glenn Barnas from Inno-Tech, who provided invaluable information when I needed it most.

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