Category Archives for "Russ White"

Research: Measuring IP Liveness

Of the 4.2 billion IPv4 addresses available in the global space, how many are used—or rather, how many are “alive?” Given the increasing usage of IPv6, it might seem this is an unimportant question. Answering the question, however, resolves to another question that is actually more important: how can you determine whether or not an IP address is in use? This question might seem easy to answer: ping every address in the address space. This, however, turns out to be the wrong answer.

Scanning the Internet for Liveness. SIGCOMM Comput. Commun. Rev. 48, 2 (May 2018), 2-9. DOI:

This answer is wrong because a substantial number of systems do not respond to ICMP requests. According to this paper, in fact, some 16% of the hosts they discovered that would respond to a TCP SYN, and another 2% that would respond to a UDP packet shaped to connect to a service, do not respond to ICMP requests. There are a number of possible reasons for this situation, including hosts being placed behind devices that block ICMP packets, hosts being configured not to respond to ICMP requests, or a server sitting behind a PAT or CGNAT Continue reading

Network Troubleshooting Webinar on Safari Books

I just redid my slides for the network troubleshooting seminar I teach on Safari Books from time to time. This new set of slides should make for a better webinar. The outline now covers—

Segment 1: Foundations
Length: 50 minutes

  • Resiliency in terms of troubleshooting
  • Positive feedback loops
  • Automated processes and fragility
  • The troubleshooting process
  • Avoiding the narrows
  • Using models to dive deeper
  • Using abstraction to counter the combinatorial explosion
  • When abstractions leak
  • What, how, and why models

10 Minute Break

Segment 2: Process
Length: 50 minutes

  • The theory of half split, as seen from search trees
  • Putting it together: a simple troubleshooting loop and the half-split
  • Using manipulability theory to prove it
  • Observations on observations

10 Minute Break

Segment 3: Examples
Length: 50 minutes

  • The EIGRP case
  • The BGP case
  • IS-IS and BFD

10 minute final Question and Answer Period

You can register here. Note the name of the seminar is changing, so the URL might change, as well.

BGP Hijacks: Two more papers consider the problem

The security of the global Default Free Zone DFZ) has been a topic of much debate and concern for the last twenty years (or more). Two recent papers have brought this issue to the surface once again—it is worth looking at what these two papers add to the mix of what is known, and what solutions might be available. The first of these—

Demchak, Chris, and Yuval Shavitt. 2018. “China’s Maxim – Leave No Access Point Unexploited: The Hidden Story of China Telecom’s BGP Hijacking.” Military Cyber Affairs 3 (1).

—traces the impact of Chinese “state actor” effects on BGP routing in recent years. Whether these are actual attacks, or mistakes from human error for various reasons generally cannot be known, but the potential, at least, for serious damage to companies and institutions relying on the DFZ is hard to overestimate. This paper lays out the basic problem, and the works through a number of BGP hijacks in recent years, showing how they misdirected traffic in ways that could have facilitated attacks, whether by mistake or intentionally. For instance, quoting from the paper—

Site Work

I spent some time this week moving to a new theme, specifically Beaver Builder. It was a bit more work than I expected because of some serious limitations with the way Beaver Builder works—had I known about these limitations, I probably would have worked with another product, but by the time I discovered them, it was either find a way around the limitations, or spend a lot more time and/or money working through them.

In the process, I completely rebuilt the menu, and cleaned up the categories.

The site should be a good bit faster now. I’m not entirely certain the social sharing bits are working, and I will likely find a few things wrong here and there that need to be fixed over the next few weeks. I just discovered, for instance, that I lost all the work on the papers and topical pages I’d done earlier today, so those need to be redone, which will take a good bit of time.

Network Troubleshooting at Safari Books Online

I am giving my network troubleshooting class over at Safari Books Online on the 6th of December for those who are interested. I consider this a foundational session, covering the time components of an outage, a taxonomy of reactions to outages, the half-split method of searching for the root cause, and how models can help you understand the right questions to ask to narrow a problem down quickly. A lot of this course is based on formal methods of troubleshooting I learned in electronic engineering, adapted for the networking world.

This is one of three webinars I give at Safari Books on a periodic basis; I hope to be adding a fourth in the near future.