UDP Datagram Support for DNS NAPTR Responses

The Oracle® Enterprise Session Border Controller’s default behavior is to conform to the DNS standard defined in RFC 1035 Domain Names: Implementation and Specification, which sets a maximum size for UDP responses of 512 bytes. This limitation means that responses larger than 512 bytes are truncated (set with the TC, or truncation, bit). In addition, this limitation protects network and system resources because using TCP consumes an undesirable amount of both.

However, you can configure support ENUM queries that manage larger UDP DNS responses as set out in RFC 2671, Extension Mechanisms for DNS (EDNS0), enabling your Oracle® Enterprise Session Border Controller to manage responses beyond 512 bytes. According to RFC 2671, senders can advertise their capabilities using a new resource record (OPT pseudo-RR), which contains the UDP payload size the sender can receive. When you specify a maximum response size over 512 bytes, then the Oracle® Enterprise Session Border Controller add the OPT pseudo-RR to the ENUM query—without which the ENUM server will truncate the response.