Posts by Russ

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 device that only passes through service requests rather than all packets.

The paper begins by building a taxonomy of liveness, describing the process they use to determine if an address is in use or not, as shown in the image replicated from the paper.

One problem of note is that address usage can shift over time; between trying to use ICMP and a TCP SYN to determine if an IP address is in use, the device connected to that address can change. To limit the impact of this problem, the researchers sent each kind of liveness test to the same address close together in time. The authors then attempt to cross reference the liveness indicated using different techniques to an overall view of liveness for a particular address.

The research resulted in a number of interesting observations, such as the 16% of hosts that respond to TCP SYN probes on some port, but do not respond to ICMP requests. The kinds of ICMP and TCP responses was also quite interesting; many TCP implementations do not seem compliant to the TCP specification in how they respond to a SYN request.

Along the way, the authors added new capabilities to ZMap which allow them to perform these measurements. The tool they used has a web based frontend, and can be accessed here.

The results are interesting for network operators because they indicate the kinds of work required to find all the devices attached to a network using IP addresses—a mass ping utility is simply not enough. The tools developed here, and the lessons learned, can be added to the set of tools used by operators in all networks to better understand their IP address usage, and the shape of their networks.

Weekend Reads 110818

KrebsOnSecurity recently had a chance to interview members of the REACT Task Force, a team of law enforcement officers and prosecutors based in Santa Clara, Calif. that has been tracking down individuals engaged in unauthorized “SIM swaps” — a complex form of mobile phone fraud that is often used to steal large amounts of cryptocurrencies and other items of value from victims. Snippets from that fascinating conversation are recounted below, and punctuated by accounts from a recent victim who lost more than $100,000 after his mobile phone number was hijacked. @Krebs on Security

PortSmash, as the new attack is being called, exploits a largely overlooked side-channel in Intel’s hyperthreading technology. A proprietary implementation of simultaneous multithreading, hyperthreading reduces the amount of time needed to carry out parallel computing tasks, in which large numbers of calculations or executions are carried out simultaneously. The performance boost is the result of two logical processor cores sharing the hardware of a single physical processor. The added logical cores make it easier to divide large tasks into smaller ones that can be completed more quickly. —Dan Goodin @ARS Technica

Security researchers have unveiled details of two critical vulnerabilities in Bluetooth Low Energy (BLE) chips embedded in millions of access points and networking devices used by enterprises around the world. Dubbed BleedingBit, the set of two vulnerabilities could allow remote attackers to execute arbitrary code and take full control of vulnerable devices without authentication, including medical devices such as insulin pumps and pacemakers, as well as point-of-sales and IoT devices. —Swati Khandelwal @The Hacker News

Crooks who hack online merchants to steal payment card data are constantly coming up with crafty ways to hide their malicious code on Web sites. In Internet ages past, this often meant obfuscating it as giant blobs of gibberish text that was obvious even to the untrained eye. These days, a compromised e-commerce site is more likely to be seeded with a tiny snippet of code that invokes a hostile domain which appears harmless or that is virtually indistinguishable from the hacked site’s own domain. @Krebs on Security

Over the last several years, Facebook has gone from facilitating the free flow of information to inhibiting it through incremental censorship and account purges. What began with the ban of Alex Jones last summer has since escalated to include the expulsion of hundreds of additional pages, each political in nature. And as more people become wary of the social media platform’s motives, one thing is absolutely certain: we need more market competition in the realm of social media. —Brittany Hunter @Interllectual Takeout

Tim Berners-Lee, a London-born computer scientist who invented the Web in 1989, said he was disappointed with the current state of the internet, following scandals over the abuse of personal data and the use of social media to spread hate. “What naturally happens is you end up with one company dominating the field so through history there is no alternative to really coming in and breaking things up,” Berners-Lee, 63, said in an interview. “There is a danger of concentration.” —Guy Faulconbridge, Paul Sandle @Reuters

It’s been three years since Australia adopted a national copyright blocking system, despite widespread public outcry over the abusive, far-reaching potential of the system, and the warnings that it would not achieve its stated goal of preventing copyright infringement. Three years later, the experts who warned that censorship wouldn’t drive people to licensed services have been vindicated. According to the giant media companies who drove the copyright debate in 2015, the national censorship system has not convinced Australians to pay up. —Cory Doctorow @EFF

Thiel said Silicon Valley has fallen victim to groupthink, citing its politically insular atmosphere for his moving away to Los Angeles. “There’s a sense that the network effects that made Silicon Valley good have gone haywire,” he said, according to CNBC. “It’s not the wisdom of crowds, it’s the madness of crowds.” @Market Watch

Google Chrome is the most popular browser in the world. Chrome routinely leads the pack in features for security and usability, most recently helping to drive the adoption of HTTPS. But when it comes to privacy, specifically protecting users from tracking, most of its rivals leave it in the dust. —Bennett Cyphers and Mitch Stoltz @EFF

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.