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Showing posts from April, 2014

Extension Mechanisms for DNS (EDNS0)

DNS Background The Domain Name System Protocol was first designed in 1980s and after that various features has been added while maintaining the compatibility with earlier versions of the protocol. DNS Packet was restricted to UDP 512 bytes in the early releases while keeping in mind the minimum MTU size is of 576 bytes in IPv4. This has been done to check the issues of packet drops, fragmentation and others. This packet size limit of 512 bytes also led to limit the number of root servers to 13 (A to M). In 1999, Paul Vixie proposed extending DNS to allow new flags and Response Codes, and to provide support for longer responses which should also be backward compatible with previous implementation. Mechanism Due to limitation of space in DNS header, no new flags can be added in it. EDNS add information to DNS message in the form of pseudo-RRs included in the ‘additional data’ section of DNS message. This section exist both in Request and Response. The pseudo-RR introduc