Domain Name System (DNS) is a major target for the network security attacks due to the weak authentication. A security extension DNSSEC has been proposed to introduce the public-key authentication, but it is still on the deployment phase. DNSSEC assumes IP fragmentation allowance for exchange of its messages over UDP large payloads. IP fragments are often blocked on network packet filters for administrative reasons, and the blockage may prevent fast exchange of DNSSEC messages. In this paper, we propose a scheme to detect the UDP large-payload transfer capability between two DNSSEC hosts. The proposed detection scheme does not require new protocol elements of DNS and DNSSEC, so it is applicable by solely modifying the application software and configuration. The scheme allows faster capability detection to probe the end-to-end communication capability between two DNS hosts by transferring a large UDP DNS message. The DNS software can choose the maximum transmission unit (MTU) on the application level using the probed detection results. Implementation test results show that the proposed scheme shortens the detection and transition time on fragment-blocked transports.

Ad hoc networks are comprised of MAC, routing protocols and physical environments. In this paper, optimum MTU (Maximum Transmission Unit) sizes are studied in the ad hoc network environment. For a performance index, the "throughput rate" is defined. The throughput rate is the ratio between the number of packets received and packets sending through the overall systems. MTUs with the sizes between 250 bytes and 750 bytes have been shown to have better throughput rates in the environment without noise. MTUs with the size of 500 bytes have been found to generate the optimum throughput rate in the environments of 10-4 BER or less. Similar results are obtained in lower BER environments. AODV has slightly better performance than DSR without noise. These results found to be true for practical mobile environment.