Network Zoning (The Zone)

I decided to start a series on Network Zoning after seeing too many “you need to zone your network” articles and best practice guidelines that never give any aide to the reader on HOW to go about this other than segregate your network or firewall off the servers. Before you attempt this, make sure you understand the limitations of your infrastructure and the concepts outlined below.

In this series, a ‘Zone’ will be the LAN segment set aside for a specific function or IP Range. This zone will route or switch to a firewall-like interface which will provide the “networking” part of the puzzle between the various zones. Depending on the ruleset, data from one zone may or may not be transported to another zone.

Make sure you’re familiar with TCP/IP, Networking, VLANs, IP Addresssing, and subnets; you don’t need to be an expert to proceed. The examples, configurations, and how-to will assume you’re working with Cisco equipment. If you need help with other equipment, you’re welcome to drop me a line.

In this example, the zoning will be accomplished by assigning like-resources to a specific VLAN and having these VLANs end on a router/firewall interface whereBasic Network Zoning access decisions can be made in accordance with local Security Policies and Practices. 

First thing’s first.

Zoning implies some grouping of computing resources. This grouping could be by location, function, purpose, access type, subnet, etc. Because this is my how-to, I’m going to zone according to functional area and subnet. Take a look at this basic diagram where users, administrators, application servers, and sensitive data servers are zoned off and tie back to a firewall.

Functional zoning is very beneficial once the firewall side comes into play because the access rules and restrictions should be largely similar across the specific zone. All the servers shouldn’t need Y! Instant Messenger access but the Desktop Users might run The Weather Channel on their desktop. Zoning like resources makes management of the firewalling and routing simpler over-time as well, because the zoned areas can be extended without re-inventing the wheel.

Once you know how you want to group the resources, it is important to describe and qualify what is unique and different about each grouping. This ensures that your groups don’t overlap as well as preserves the groupings going forward. Depending on your experience with firewalling and routing, at this point you may want to begin clarifying what each zone can and cannot access, for instance – the Sensitive Data Servers DO NOT surf the web or have access to email.

The example here assumes the subnets of these groups allows for grouping or summarization, this may or may not be the case in your grouping but if you have the options it does simplify things in other areas as well. For my example I have allocated 256 IP Addresses to each of the two server zones along with the administrator zone and I have allocated 1024 IP Addresses for the user zone:

  • Zone – APPS = 10.0.0.0/24 (10.0.0.0 – 10.0.0.255) [256 Server IP Addresses]
    • Description: Zone dedicated to application servers and services, no end-users and no sensitive customer data
    • Examples: Intranet server, Email server, File server
  • Zone – SENSITIVE = 10.0.1.0/24 (10.0.1.0 – 10.0.1.255) [256 Server IP Addresses]
    • Description: Zone dedicated to servers that contain sensitive customer data (could also be employee data)
    • Examples: Oracle database server
  • Zone – SYSADMIN = 10.0.2.0/24 (10.0.2.0 – 10.0.2.255) [256 System Administrator IP Addresses]
    • Description: Zone dedicated to privileged administrators of systems, applications, or infrastructure, requires extra access to servers, network elements, etc.
    • Examples: Network Management Team, Firewall Administrators, Database Administrators, etc.
  • Zone – USERS = 10.0.3.0/22 (10.0.3.0 – 10.0.6.255 [1,024 Desktop User IP Addresses
    • Description: Zone dedicated to the general user base
    • Example: Average Joe user

These examples and zones will  not apply to every organization. These are hypotethical and designed to get your imagination flowing. The key ingredient is being able to combine ‘like users’ and ‘like access’. The zone members will be placed into their own VLAN and will not be able to talk to devices outside their VLAN unless a router or firewall allows them to do so. In the example above, this VLAN configuration will allow the use of routed VLAN interfaces and switched VLAN interfaces. The difference between routed and switched interfaces being: switched interfaces only talk to similar switched interfaces (ZONE-USERS talks to ZONE-USERS over switched interface while ZONE-USERS cannot talk to ZONE-APPS without passing through a routed interface).

There is one more zone to introduce, that I have come to rely heavily on, ZONE-NETCORE. If you think about it, you’ve zoned the users, the applications, and the servers. What about the network?

  • Zone – NETCORE = 10.255.0.0/24 (10.255.0.0 – 10.255.0.255) [256 Network Core IP Addresses]
    • Description: Zone dedicated to network interface on routers to facilitate core communications and isolate zones
    • Examples: each router has an interface on this Zone

The ZONE-NETCORE is not required, but it serves to isolate the VLANs from one-another across a core or the network, without this zone each VLAN/ aka Zone must come all the way back to the firewall, as indicated in the basic diagram. This approach creates communities that are aggregated and connected via conduits, as depicted here. Note each zone is self-contained and isolated from other zones before reaching the firewall.

Now we have zones defined and understand basic functionality inside the zones. How are the VLANs setup? What security do we need for each zone and how is that accomplished?

Stay tuned…

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Posted on October 15, 2007, in How to's and tagged , , , , , , . Bookmark the permalink. 4 Comments.

  1. i also have done some research on network zoning and i will be posting my experience with the concept. pls. check my web site fathi.fathialwosaibi.net

    • Interesting post on your site.

      I must apologize I got tied up in so many things I’ve neglected this site and my Web Security sites. I’ll be updating the content here as well as the other sites.

      RE: Zoning.
      It’s possible to make the zones too complicated to manage, so be sure in any Network Redesign, Security Rebuild, or Risk Management strategy to consider the operational footprint of the end-state on the business.

      Often times Network Zoning will introduce new business processes that can become too rigid to maintain. The end result is the weakening of the zone defenses. The best way to combat such an issue is to consider the maturity of the business and typical operational needs. I would never recommend a rigid, complex security program for a business that is likely to bypass the resulting processes and procedures that Network Zoning introduces.

      Cheers!
      Brian

  2. thanx for the reply;
    actually zoning will simplify network administration, and from my experience when you zone you basically lay down the foundation which should be rigid and fixed. i did add an article in my web site about Zoning Conceptual Design. Pls. check it out in my web site

    you can get it through this link: http://fathi.fathialwosaibi.net/index.php?option=com_content&view=category&layout=blog&id=1&Itemid=4&lang=en

    good luck;

  1. Pingback: Network Zoning – Be the Zone « Practical Tactics

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