The Domain Name System (DNS), which is part of essentially every transaction on the Internet, has also become a critical part of many online attacks. Now, a monitoring framework presented at IETF 104 in March is providing new insight into the way DNS queries are received and answered across the Internet, as well as how that process might have an impact on security.
The DNS Observatory is a research project backed by Farsight Security. It allows researchers to see details of the queries and traffic flowing between recursive DNS resolvers (the kind most users query when they type in a website name) and authoritative name servers (the DNS servers that keep the canonical list of Web names and addresses).
According to Farsight, the DNS Observatory looked at streams of passive observations between recursive DNS resolvers and authoritative name servers. The Observatory processed over 1 trillion DNS transactions from January to March and saw over 2.5 million unique Fully Qualified Domain Names (FQDNs) per minute, on average.
One of the primary findings from that is that the vast majority of DNS resolution requests are made through a relative handful of servers. "Approximately 60% of the DNS transactions captured in our list were handled by just 1,000 name servers; the majority of queries flowed into ASes [authoritative servers] operated by less than 10 organizations," according to Pawel Foremski, scientist/senior distributed systems engineer at Farsight.
Paul Vixie, founder of Farsight Security, points out that this concentration of requests can represent a significant security risk for the global Internet. "I'd say it seems to be a lot of eggs in a small number of baskets," he says. "We're not seeing the kind of organizational diversity that characterized the earlier internet."
Vixie explains that the limited number of authoritative name servers, coupled with subtle server behaviors regarding how long servers will try to respond to queries for a nonexistent domain or those involving both IPv4 and IPv6 addresses, means the time for resolving names has crept up over time. "Some of the transaction times here are almost a tenth of a second to reach some pretty popular domains," Vixie says.
While that's not a time likely to be perceived by a human user, it is enough time to create opportunities for attacks involving DNS. "When Dan Kaminsky came up with his novel attack on DNS transactions in 2008, it turned out that the time taken for a content server to answer a question from one of these recursive servers controlled the number of opportunities that the attacker would have to try to guess the various combinations of numbers that were in the transaction," Vixie says.
While increasing the number of authoritative servers could speed the transaction time for DNS resolution and minimize one set of risks, the possibility exists that the same action would increase other risks, Vixie says. "There is no way to separate the benefits and the costs of scale," he says. "If we add a lot more name servers, then we will be adding more computers that have to be audited, upgraded, and fixed when they break."
Vixie points out that these additional servers will need additional trained staff. The complexity will increase the attack surface for malicious actors to work on, and that attack surface will demand additional monitoring and protection. "There's no way to avoid that," Vixie says.
Farsight Security says it will make DNS Observatory data available to other researchers and invites ideas for its use.