Endpoints and Network Integration

Addison Wesley Professional

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Do I Need a Forklift?

As I pointed out earlier, not all network infrastructure devices can support your decision to rely on 802.1x. As our networks have grown and expanded over the years, most of us have accumulated different vendors and different versions of each vendor's equipment. Not all of them are going to have the same capability. Add to that the fact that there are hundreds of thousands of "dumb" switches (or worse, simple hubs), and you begin to see how the problem can get out of hand quickly.

Some of us are going to have to rip out and replace a lot of equipment.

Upgrades Are Expensive

Hardware vendors love change. Change means that they get to sell more hardware! When people stop buying new hardware or upgrading the hardware they have, the "network iron" companies are going to go out of business. We saw this happen when the "bubble" burst. Folks were waiting on the "killer application," and in anticipation other folks went crazy installing lots of fiber and infrastructure. One day someone woke up and said, "Hey, we have a lot of dark fiber out there and no killer application to fill it with bits. Maybe we should stop buying stuff."

Stall, spin, crash, burn, die.

The resulting crash didn't really lower the price of equipment, unfortunately. My most recent data on this comes from a financial customer who was planning on upgrading to all 802.1x-capable devices. He called his network hardware vendor in for a chat and told him what he was planning on doing. The vendor told him that all his hubs would have to be replaced because 802.1x only allows one connection per port and each new connection would need authentication and would kill the last connection. Most users would classify that as "bad." Some of my friend's switches were a couple of years old, and they didn't have the memory capacity for the new code; and because they were so old, they couldn't have more memory added. They would have to be replaced. However, a good number of the switches could be upgraded and would have to be to support the 802.1x-capable code. Yay! Now, you probably need some professional services people to help with such a huge upgrade. After all, a lot of details and configuration changes need to be accounted for. Oh, and he needed a "good solid project manager" to pull all those PS people together. By the time it was over, my friend was looking at a $2 million plus, one year to complete, "you get to keep the forklift" upgrade.

Let's not mention the time and potential for disaster as far as the user is concerned. New devices become the excuse of choice. "Because your fill-in-the-blank burped, I missed my delivery date!"

The good news is that he was able to convince his board that it was more important to be a leader in the security space than tomorrow's headlines, and they're well on their way to implementing a CLPC-enforced network.

A Less-Expensive Way

So, you don't want to help your local network rep make the payments on his shiny new BMW? There is a cheaper way. It's not as effective, but it does work. I say "it's not as effective" because it relies on voluntary participation.

Instead of relying on the switch to make the decision, you can use the fact that Internet Protocol (IP)-based endpoints use the IP address and its associated subnet mask to accept traffic. You can use this to your advantage in a kind of bastardized implementation of the IP protocol. By using DHCP, you can control if and how an endpoint talks to the network. This works because switches operate at Layer 2 and routers operate at Layer 3. By using switches to make connections between individual endpoints based on Media Access Control (MAC) addresses and by using the routers to control how networks communicate using the IP address, you can gain a great deal of control over all the endpoints on your network.

Let's take a look at how this works by starting with the DHCP protocol. The Dynamic Host Configuration Protocol,4 DHCP for short, evolved out of the Bootstrap Protocol (BOOTP) that was used in the early days of the Internet. DHCP is backward compatible with BOOTP and supports the idea of a lease. Instead of being given an IP address in perpetuity, DHCP lets you use the IP address only as long as the lease is valid. When the lease expires, the DHCP client on the endpoint "releases" the IP address back to the DHCP server.

If your endpoint isn't configured with a static or fixed IP address, it's usually set to ask a DHCP server for an address. You usually get your first DHCP lease when the endpoint first joins the network, but there are other times when you can get one. Many operating systems come out of the box with the network configured to talk to a DHCP server.

The complete protocol exchange is fairly elegant. The requesting endpoint sends out a broadcast packet with a destination address of all 1s and a source address of all 0s. A listening DHCP server responds with a packet that has the IP address, the subnet mask, the default gateway, the length of the lease, and at least one DNS server, as shown in Table 5-1.

Table 5-1 A Simple DHCP Network Scope



IP address

Subnet mask

Default gateway

Duration of lease in seconds


DNS server

It can send more information, especially if you're a Microsoft endpoint, but we'll stop at this level of detail because this isn't a book about the DHCP protocol. After the endpoint has received the IP address information, it sends a message back to the server acknowledging that it's going to use the address.

Using the information in the table, we can see that our endpoint is now equipped to access the network for two hours. When two hours is up, it will have to ask the DHCP server again for an address.

So, why is this cool, and how can we use it to our advantage? To start, it's cool because most of us are lazy and DHCP makes it easy to support an IP-based network, because you don't have to configure static IP addresses and mess around with all the information that goes with them. Each time you touch an endpoint is an opportunity to screw it up, and you eliminate that with DHCP. The downside is that if you misconfigure the DHCP server, you can really "screw the pooch" for all of your users.

How can we use this to our advantage? Easy, most DHCP servers can manage multiple scopes. A scope is a geek term that defines each set of parameters for each set of IP address ranges that the DHCP server will be giving out. One scope may say that the IP address range has the parameters depicted in Table 5-1, whereas another scope has the parameters defined in Table 5-2. In Table 5-2, the top scope serves as the remediation scope; the bottom scope allows connections to the production network.

Table 5-2 Two DHCP Scopes



IP address range start

IP address range end

Default gateway

Subnet mask

Duration of lease in seconds


DNS server

IP address range start

IP address range end

Default gateway

Subnet mask

Duration of lease in seconds


DNS server

Scopes are usually associated with networks, but this can be worked around with third-party software, hardware, or magic.

If you figured that one scope was for a trusted network, and the other was for an untrusted network, you understand what we're trying to do here. When an endpoint starts up, it gets an address in the untrusted or quarantined network. When it can prove to the DHCP server that it can be trusted, the DHCP server gives it an address in the trusted enterprise network.

The magic part has to do with how routers handle DHCP requests. Because a DHCP server might not be on the same network segment as the client, the router has to tell the DHCP server what network the client requesting the DHCP request lives on. So, when a router sees the DHCP request, it appends what network the packet came in on to the packet. The DHCP server uses that information to decide which scope to serve an address from. DHCP enforcement uses that to select what network the endpoint is going to be assigned to. The network access control (NAC) client appends compliance information, the router appends network information, and the information is taken apart and sent to the DHCP enforcer/server. There are multiple ways to do this, and it depends on the vendor what method is used. It could be a change to the DHCP software, or it can be a proxy server in front of the DHCP server.

Why does this work? Because routers can support multiple IP address ranges on their interfaces, thereby allowing routable and unroutable IP address ranges on the same network. For that matter, if a router doesn't know about an IP address range, it would look like spoofed addresses and drop the packets. Instant containment! In Figure 5-5, the endpoints inside of the dotted box will not have access to the rest of the network because their IP address won't be passed by the router.

Figure 5-5

DHCP enforcement. Through clever use of proxies and routers, DHCP NAC enforcement provides containment.

Now that we've looked at why DHCP works, let's consider why it doesn't work. It's voluntary. If I decide that I'm going to manually assign an IP address from an observed list of IPs, I can defeat DHCP enforcement. You should consider DHCP a migration mechanism, but completely relying on it probably isn't the best idea in the long run.

Technology Promises and Futures

Technology got us here, and technology is going to save us. I can prove it! Technology has been getting us "here" for the past 50 years. Since the first computer, technology has been promising us a better future, and it's going to save us sometime real soon. Any moment now technology is going to ride up on a big white horse and save our butts. I'm not holding my breath, however.

Just as technology provides a savior, technology will also provide three new adversaries. We'll add enforcement to our solution, but like a water balloon that you squeeze in the middle, our problem will pop out somewhere else. If we continue to treat technology as a series of point solutions designed to solve our problem of the moment, we're going to be disappointed for a long time to come.

So, what does the future hold? Not much if we don't change our ways. We can't continue to let the vendors drive our solutions through marketing and the threat du jour. The future of security is hinged on turning it into an engineering domain complete with processes and postulates. From these postulates, we will be able to craft specific tests, run the tests, analyze the test results, and see whether they agree with our postulates. If they do, we're one step closer to better security. If not, we can reexamine and reformulate our postulates.

We can set some milestones, but when we get to them, we need to be ready to move on to the next one. As we secure our environment, we need to turn our attention to the data that we're generating.

In the previous paragraphs, we talked about compartmentalizing our networks to protect them. One of the methods was the compartmentalization of the network based on the data classification. Using our present operating system architectures, that's about all we can do. We don't have labels, and we can't make decisions based on the classification of the data. Sure, third-party data protection solutions do exist, but they're bolt-ons and as such aren't a part of the consideration put into the operating system.

Endpoint Support

How well our solutions work is going to be based on vision, simplicity, and common sense. Each endpoint is going to have to receive a different kind of support because each endpoint type has a different user profile associated with it. Some endpoints, such as our industrial controllers, don't have users per se; they have "actors," such as "bots."


Authentication used to be about identifying the user. In recent years, the definition has expanded to encompass the system to a certain degree. Through the use of certificates, you can be fairly certain that you're really talking to the server that you intended to talk to.

The Trusted Computing Group (TCG) has expanded the authentication mechanism such that it now includes the hardware. This is a great thing because it should reduce the incidence of notebook theft in the future by making it easier to trace (and therefore harder to sell) the stolen property. However, it should be said that all the Trusted Platform Module (TPM) really is, is a secure place to store keys and certificates. As we are so painfully aware, each security solution that we've come up with in the past has been bypassed or otherwise broken, thereby keeping us on the wheel of pain.

For the purposes of CLPC and NAC, we're going to include a trust element in our authentication protocol. This trust element will include a determination regarding the state of the endpoint. In short, it will examine whether the endpoint meets a preset level of compliance and thus an implied level of trust.

Vendor Support

As I've said, there aren't a lot of options out there to help with integrating our endpoints and our networks. We're counting on NAC (in whatever form) to help, but vendors are working to get into the market. A bit of a warning here: The following information was accurate as of this writing. Vendors change directions fairly quickly, and although there are the expected offerings from Cisco and Microsoft, both pushing their respective solutions, this could change the day after publication.

Hardware vendors such as Enterasys, Foundry Networks, Extreme Networks, and Juniper Networks presently provide some, if not all, parts of the solution.5 Juniper bought Funk and the Steel Belted Radius product line; and with that, combined with their existing product line, they seem to offer something that has everything except endpoint integrity compliance.

Enterasys literature shows them doing a remote scan of the system, and they claim that their agent solution, Trusted End-System Solution, works with their other products that manage policy and authentication, authorization, and auditing (AAA).6 A deeper look into their products indicates that Enterasys relies on Sygate (now Symantec) and Zone (now Check Point) agents to check integrity.

Foundry has taken the same approach that Enterasys has—not too strange considering Foundry is a hardware vendor.7 To make their solution work, you need a good agent on the endpoint, and that means Symantec or Check Point. The combination of Foundry and Symantec is a solution that I've personally seen work. It took a bit of work to get the remediation part to work because it had to have some custom scripts, but it did work.

Extreme has also teamed up with another vendor (in this case, StillSecure) to provide a multitude of NAC solutions.8 They claim to provide agentless testing through the StillSecure Safe Access solution. This process uses Windows Remote Procedure Call (RPC) and credentials to interrogate the endpoint, so each endpoint must be configured to accept StillSecure access to accomplish testing. Your endpoint firewall will have to be configured to allow this type of access. Thankfully, we haven't seen any buffer-overflow vulnerabilities in RPC that allow an attacker to execute arbitrary code since late 2003.9 But, if using Windows RPC makes you nervous, you can always use the browser-based ActiveX tool! If you want to avoid the remote execution of code that MS06-014 says is possible (unless you patch "at the earliest opportunity"),10 however, you can always use the StillSecure agent.

Symantec now has a NAC offering thanks to its purchase of Sygate. The Symantec Sygate Enterprise Protection (SSEP) solution is an agent-based solution that leverages 802.1x (an additional module), DHCP, or network compartmentalization. The agent is capable of doing self-enforcement, thereby eliminating reliance on 802.1x or DHCP. However, a basic rule of security is that if you can put your hands on it, you can break into it. Self-enforcement is a last resort if you have no other options and you don't have a very sophisticated user community. SSEP does have an integrity component that ensures that the system has the required software and patches and actively prevents malware from infesting the machine. Operating system protection examines how system calls are made; if they exhibit unknown behavior, the call is terminated.

The Symantec/Foundry combination is also a solution that I have seen work. By using the 802.1x capability of the Foundry FastIron switch, noncompliant endpoints were switched to a remediation LAN where they could be repaired. SSEP provides remediation services as well as interfacing with third-party remediation and patch-management products.

Check Point Integrity has a similar set of features with respect to NAC, but it wraps VPN support and integration with other Check Point security products into the mix. Integrity also has an endpoint integrity option that can be used to evaluate the security state of the endpoint and, if needed, initiate remediation actions or quarantine.

Cisco and Microsoft, as of this writing, have yet to completely deploy their solutions. They seem to have a good set of visions, but the implementation side is a bit slow.

Infoblox11 is an interesting solution because it's a toolkit that only addresses DHCP-based NAC. Let me draw an analogy here. You walk into a pet shop and ask for a dog. The clerk asks, "What kind of dog do you want?" Check Point and Symantec products are kind of like that pet shop. Do you want DHCP, 802.1x, compartmentalization, or do you want a mutt? On the other hand, you can walk into a pet shop, ask the clerk for a dog, and the clerk can hand you some DNA and tell you that you can make any kind of dog you want. Toolkits are like that.

Vulnerabilities and Remediation

As mentioned earlier, an incredible industry is devoted to just identifying and classifying vulnerabilities on your network. Companies such as Qualys and nCircle have successfully implemented a business model that feeds on vulnerability detection and analysis.

I suppose that I should be clear when I make this next point because I'm about to poke some folks in the eye with a stick. The marketing model for the vulnerability assessment (VA) industry is predicated on two things:

  • Eliminating exposed vulnerabilities will make you secure.

  • The scan, repair, scan model is effective.

I submit that there are more problems with this "hacker's eye view" than vendors would lead you to believe.

First, your network is changing faster than you can scan it. At best, a scan is a snapshot of a very quickly moving set of scenes. Imagine trying to figure out what a movie was about by looking at every ten thousandth frame!

Second, the mere act of scanning a network can create problems by itself. If you have any kind of intrusion detection software, it's sure to alert on the fact that the endpoint is being scanned. Sure, you can add exceptions to your network-based intrusion detection system (NIDS) and your host-based intrusion detection system (HIDS), but you have to do that every time your scanning source changes. Even with that, some applications don't like being scanned and may behave by crashing or slowing down to the point where service levels are affected.

Third, although they can be configured to, these scans don't scan every port. They only scan a comparatively small number of ports. If someone wanted to hide an illegal application, it wouldn't be hard.

Scans are also insensitive to where the endpoint is on the network. A vulnerability is a vulnerability.

So why scan at all? Well, a simple answer to that is that it helps an organization meet the regulatory requirements of outside assessment. Sarbanes-Oxley (SOx) is a perfect example of this. You can have the best security in the world, but you still need an outside assessment to fill a check box. Am I opposed to outside assessments? No, I'm not. I just think that if you're going to spend your money, there are better ways to spend it. Get an occasional scan, but be careful how much you pay for it. This type of service is now a commodity. And remember that you still have to remediate what you find at some point in time.


Now that I've completely bashed the VA market, we can talk about how to detect vulnerabilities in your endpoints. You can use a couple of methods to detect vulnerabilities. The first I talked about in the previous pages: You can scan and hope for the best. But as I discussed, scanning does have its downside. Besides the reasons I mentioned before, I believe that scanning is reactive and inaccurate.

Another, and I believe more effective way, is to keep track of what's added or removed from the endpoint. If you know what's on the endpoint, you can compare that to a known list of vulnerabilities and make a determination of risk and exposure.

That means that you have to have access to the endpoint either through a smart agent that provides an inventory function or via a remote protocol.

Another way to do that would be to install inventory software that keeps track of what software is loaded on the system. It doesn't operate at the frequency that NAC requires, but it does give you some feedback as to what's living on your endpoints.

Vulnerability Tracking Services

Multiple services track vulnerabilities, and you can use that information to check your endpoints for vulnerabilities. Most sites use a naming format called the Common Vulnerabilities and Exposures, or CVE, to name their vulnerabilities. CVE allows publishers of vulnerabilities to use a common dictionary of terms in the hope that it will allow us to more effectively communicate. You can find these databases as follows:

Vulnerability Management

So, what's the difference between vulnerability management (VM) and vulnerability scanning? Commitment to the process. VM is about taking information that you have about the state of your endpoints, their vulnerabilities, and understanding what type of mitigation to employ. Once again, there is a subtle tone to what I'm trying to say here. Just because you have a vulnerability doesn't mean that you have to rush out and install a patch. VM is not blind faith in the ability of vendors to perfect their offerings. It's about understanding how the vulnerability, potential exploits, and your business processes intersect to form a workable solution.

VM is based on a process that constantly reassesses your vulnerability posture while applying controls to ensure that business objectives are appropriately met. You can use the scan, evaluate, assess, prioritize, implement, verify cycle as a basis for your process. Most of us recognize this as the basic test, analyze, fix process, albeit with some needed controls to ensure success. As you read the next few paragraphs, use Figure 5-6 as a reference.

  1. Scan. Using either the hacker's eye view of a VA scanner or the system owner's view of an agent or inventory control tool, generate a list of your vulnerabilities based on all your installed software.

  2. Evaluate. Determine your level of exposure based on available exploits and proximity to attack. What is the risk of the exploit being used successfully against your vulnerability? Does the vulnerability have any nasty interactions with other vulnerabilities? What is the proscribed course of action?

  3. Assess. Determine how the patch or fix is going to impact your production processes. Is the patch going to require the rewriting of custom code? Does the fix really mitigate the vulnerability? Is the fix worse than the risk?

  4. Prioritize. Determine which systems are going to get your critical resources based on their value to the organization, risk of successful attack, and ability to act as a jumping-off point.

  5. Implement. Install the patches, change the procedures, or remove the offending object. It could be code, as in the case of Windows needing a patch, or it could be a case of something like a Napster, which needs to be removed. Or, as discussed in the section "Penetration Testing," it could be that a procedure has to be changed.

  6. Verify. You need to ensure that the dictated remediation has been accomplished. This could be a rescan or it could be an audit. For that matter, it could be a full-up penetration test. At any rate, you need to verify that the fix really has been implemented. I recommend that whatever process you use that you keep the verification out of band, or outside of, the normal VM process. This will act as a check and balance to your overall VM process.

  7. Start again.

Figure 5-6

The VM process defines a set of procedures that discover and manage vulnerabilities in a network environment.


Painless. Transparent. Those two words, in my opinion, accurately describe the two most important qualities of a remediation process. Sure, remediation has to be reliable and accurate, but remediation has to be painless or transparent; otherwise, people will find ways around it. If it's too restrictive or time-consuming, remediation will be viewed as "one of those productivity-sucking security processes" and will eventually get bypassed by management at crunch time.

When AV first came out and files were quarantined such that the email admin had to release them, people went around the process by copying files to floppy disks (remember those?). The viruses of the time still spread because people just afforded the malware a different carrier via removable media. The AV vendors had to include a new feature that allowed the AV engines to scan floppies. And thus, the typical weapons escalation profile continues.

To address this problem, some vendors have built what they call "automated" remediation tools. The notion is that when the user connects, a determination is made regarding the user's patch level. I say "patch level" because most of the remediation vendors are either in the vulnerability management space or the patch management space.

Penetration Testing

Let's start this section by saying that social engineering is a method of circumventing technology controls through the manipulation of people. We'll get back to this in a few paragraphs.

It is the goal of penetration testing to see how resistant your enterprise is to attack. The process starts by learning about the target. So you start by asking a few simple questions:

  • What does the target do; what is their business?

  • What is the target's threat profile?

  • Does the target rely on network technology?

From these basic questions, many more can be asked, but you really need to start from there.

By finding out what the target company does, you learn more about how the company is organized and what business processes they're going to have in place. Business processes can be attacked.

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