DNScup: Strong Cache Consistency Protocol for DNS

Effective caching in Domain Name System (DNS) is critical to its performance and scalability. Existing DNS only supports weak cache consistency by using the Time-To-Live (TTL) mechanism, which functions reasonably well in normal situations. However, maintaining strong cache consistency in DNS as an indispensable exceptional handling mechanismhas become more and more demanding for three important objectives: (1) to quickly respond and handle exceptional incidents, such as sudden and dramatic Internet failures caused by natural and human disasters, (2) to adapt increasingly frequent changes of IP addresses due to the introduction of dynamic DNS techniques for various stationed and mobile devices on the Internet, and (3) to provide finegrain controls for content delivery services to timely balance server load distributions. With agile adaptation to various exceptional Internet dynamics, strong DNS cache consistency improves the availability and reliability of Internet services. In this paper, we propose a proactive DNS cache update protocol, called DNScup, running as middleware in DNS nameservers, to provide strong cache consistency for DNS. The core of DNScup is a dynamic lease technique to keep track of the local DNS nameservers, whose clients need cache coherence to avoid losing service availability. Based on the DNS Dynamic Update protocol, we have built a DNScup prototype with minor modifications to the current DNS implementation. Our trace-driven simulation and system prototype demonstrate the effectiveness of DNScup and its easy and incremental deployment on the Internet.