Category Archives: Network

Solving the network visibility problem with NaaS

Network visibility is crucial for many things: making sure that the equipment works properly monitoring and tweaking the network’s performance and protecting it against attacks. “Network visibility also helps you update your cybersecurity strategy based on current threats. It’s important for the short term, as this is a very dynamic world, and for the long term because it allows an organization to improve its cyber resilience,” says Amit Bareket, CEO of Perimeter 81. The most … More

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Is your perimeter inventory leaving you exposed? Why it’s time to switch from IP to DNS

Historically, security teams and tools have used IP addresses to define their targets and scopes. But in a world where applications and networks are increasingly cloud-hosted or integrated with third-party services, IP addresses alone aren’t enough to ensure coverage. Modern perimeters are dynamic and constantly changing, which can lead organizations to have an inaccurate picture of their risk simply by failing to properly catalog what Internet facing assets they have. Testing against a stale set … More

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SD-WAN adoption growing as enterprises embrace app-centric architecture transition

The connected era and cloud-based environment have created a need to redesign network operations, according to ResearchAndMarkets. In addition, businesses find it operationally draining to utilize resources on ensuring a connected ecosystem rather than focusing on critical business issues. Software-defined Wide Area Network (SD-WAN) helps enterprises build an agile and automated environment, which is streamlined to support new-age cloud environments and traditional Multiprotocol Label Switching (MPLS) systems in a cost-efficient manner. To understand enterprise perceptions … More

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Global Information Services Company Discloses Malware Attack

A global information services company has disclosed a malware attack that affected several of its applications and platforms. On 6 May, global solutions provider Wolters Kluwer published a statement in which it confirmed that it was suffering network issues: We are experiencing network and service interruptions affecting certain Wolters Kluwer platforms and applications. Out of […]… Read More

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Firewalls and the Need for Speed

I was looking for resources on campus network design and found these slides (pdf) from a 2011 Network Startup Resource Center presentation. These two caught my attention:



This bothered me, so I Tweeted about it.

This started some discussion, and prompted me to see what NSRC suggests for architecture these days. You can find the latest, from April 2018, here. Here is the bottom line for their suggested architecture:






What do you think of this architecture?

My Tweet has attracted some attention from the high speed network researcher community, some of whom assume I must be a junior security apprentice who equates "firewall" with "security." Long-time blog readers will laugh at that, like I did. So what was my problem with the original recommendation, and what problems do I have (if any) with the 2018 version?

First, let's be clear that I have always differentiated between visibility and control. A firewall is a poor visibility tool, but it is a control tool. It controls inbound or outbound activity according to its ability to perform in-line traffic inspection. This inline inspection comes at a cost, which is the major concern of those responding to my Tweet.

Notice how the presentation author thinks about firewalls. In the slides above, from the 2018 version, he says "firewalls don't protect users from getting viruses" because "clicked links while browsing" and "email attachments" are "both encrypted and firewalls won't help." Therefore, "since firewalls don't really protect users from viruses, let's focus on protecting critical server assets," because "some campuses can't develop the political backing to remove firewalls for the majority of the campus."

The author is arguing that firewalls are an inbound control mechanism, and they are ill-suited for the most prevalent threat vectors for users, in his opinion: "viruses," delivered via email attachment, or "clicked links."

Mail administrators can protect users from many malicious attachments. Desktop anti-virus can protect users from many malicious downloads delivered via "clicked links." If that is your worldview, of course firewalls are not important.

His argument for firewalls protecting servers is, implicitly, that servers may offer services that should not be exposed to the Internet. Rather than disabling those services, or limiting access via identity or local address restrictions, he says a firewall can provide that inbound control.

These arguments completely miss the point that firewalls are, in my opinion, more effective as an outbound control mechanism. For example, a firewall helps restrict adversary access to his victims when they reach outbound to establish post-exploitation command and control. This relies on the firewall identifying the attempted C2 as being malicious. To the extent intruders encrypt their C2 (and sites fail to inspect it) or use covert mechanisms (e.g., C2 over Twitter), firewalls will be less effective.

The previous argument assumes admins rely on the firewall to identify and block malicious outbound activity. Admins might alternatively identify the activity themselves, and direct the firewall to block outbound activity from designated compromised assets or to designated adversary infrastructure.

As some Twitter responders said, it's possible to do some or all of this without using a stateful firewall. I'm aware of the cool tricks one can play with routing to control traffic. Ken Meyers and I wrote about some of these approaches in 2005 in my book Extrusion Detection. See chapter 5, "Layer 3 Network Access Control."

Implementing these non-firewall-based security choices requries a high degree of diligence, which requires visibility. I did not see this emphasized in the NSRC presentation. For example:


These are fine goals, but I don't equate "manageability" with visibility or security. I don't think "problems and viruses" captures the magnitude of the threat to research networks.

The core of the reaction to my original Tweet is that I don't appreciate the need for speed in research networks. I understand that. However, I can't understand the requirement for "full bandwidth, un-filtered access to the Internet." That is a recipe for disaster.

On the other hand, if you define partner specific networks, and allow essentially site-to-site connectivity with exquisite network security monitoring methods and operations, then I do not have a problem with eliminating firewalls from the architecture. I do have a problem with unrestricted access to adversary infrastructure.

I understand that security doesn't exist to serve itself. Security exists to enable an organizational mission. Security must be a partner in network architecture design. It would be better to emphasize enhance monitoring for the networks discussed above, and think carefully about enabling speed without restrictions. The NSRC resources on the science DMZ merit consideration in this case.