In this paper, we use real experiments to study multiple-input-multiple-output (MIMO) 802.11n rate adaptation (RA) on a programmable access point (AP) platform. Our case study shows that existing RA solutions offer much lower throughput than even a fixed-rate scheme. It is proven that all such algorithms are MIMO-mode oblivious; they do not differentiate spatial diversity and spatial multiplexing modes. We first design MiRA, a novel MIMO RA scheme that zigzags between intra- and inter-MIMO modes to address MIMO 802.11n dynamics. Second, we examine a window-based RA solution, which runs an independent RA in each MIMO mode in parallel and a signal-to-noise ratio (SNR)-based MIMO RA that differentiates modes using SNR measurements. Our experiments show that MIMO-mode aware designs outperform MIMO-mode oblivious RAs in various settings, with goodput gains up to 73.5% in field trials.

During the past twenty years the Domain Name System (DNS) has sustained phenomenal growth while maintaining satisfactory user-level performance. However, the original design focused mainly on system robustness against physical failures, and neglected the impact of operational errors such as mis-configurations. Our measurement efforts have revealed a number of mis-configurations in DNS today: delegation inconsistency, lame delegation, diminished server redundancy, and cyclic zone dependency. Zones with configuration errors suffer from reduced availability and increased query delays up to an order of magnitude. The original DNS design assumed that redundant DNS servers fail independently, but our measurements show that operational choices create dependencies between servers. We found that, left unchecked, DNS configuration errors are widespread. Specifically, lame delegation affects 15% of the measured DNS zones, delegation inconsistency appears in 21% of the zones, diminished server redundancy is even more prevalent, and cyclic dependency appears in 2% of the zones. We also noted that the degrees of mis-configuration vary from zone to zone, with the most popular zones having the lowest percentage of errors. Our results indicate that DNS, as well as any other truly robust large-scale system, must include systematic checking mechanisms to cope with operational errors.

Security and privacy are two major concerns in supporting roaming users across administrative domains. In current practices, a roaming user often uses encrypted tunnels, e.g., Virtual Private Networks (VPNs), to protect the secrecy and privacy of her communications. However, due to its encrypted nature, the traffic flowing through these tunnels cannot be examined and regulated by the foreign network's firewall, which may lead the foreign network widely open to various attacks from the Internet. This threat can be alleviated if the users reveal their traffic to the foreign network or the foreign network reveals its firewall rules to the tunnel endpoints. However, neither approach is desirable in practice due to privacy concerns. In this paper, we propose a Cross-Domain Cooperative Firewall (CDCF) that allows two collaborative networks to enforce each other's firewall rules in an oblivious manner. In CDCF, when a roaming user establishes an encrypted tunnel between his home network and the foreign network, the tunnel endpoint (e.g., a VPN server) can regulate the traffic and enforce the foreign network's firewall rules, without knowing these rules. The key ingredients in CDCF are the distribution of firewall primitives across network domains, and the enabling technique of efficient oblivious membership verification. We have implemented CDCF and integrated it with the OpenVPN software, and evaluated its performance using extensive experiments. Our results show that CDCF can protect the foreign network from encrypted tunnel traffic with minimal overhead.