RFC 3226 (rfc3226) - Page 2 of 6
DNSSEC and IPv6 A6 aware server/resolver message size requirements
Alternative Format: Original Text Document
RFC 3226 DNSSEC and IPv6 A6 requirements December 2001
server also needs to keep a state of the connection during this
transaction. Many DNS servers answer thousands of queries per
second, requiring them to use TCP will cause significant overhead and
delays.
1.1. Requirements
The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY"
in this document are to be interpreted as described in RFC 2119.
2. Motivating factors
2.1. DNSSEC motivations
DNSSEC [RFC 2535] secures DNS by adding a Public Key signature on each
RR set. These signatures range in size from about 80 octets to 800
octets, most are going to be in the range of 80 to 200 octets. The
addition of signatures on each or most RR sets in an answer
significantly increases the size of DNS answers from secure zones.
For performance reasons and to reduce load on DNS servers, it is
important that security aware servers and resolvers get all the data
in Answer and Authority section in one query without truncation.
Sending Additional Data in the same query is helpful when the server
is authoritative for the data, and this reduces round trips.
DNSSEC OK[OK] specifies how a client can, using EDNS0, indicate that
it is interested in receiving DNSSEC records. The OK bit does not
eliminate the need for large answers for DNSSEC capable clients.
2.1.1. Message authentication or TSIG motivation
TSIG [RFC 2845] allows for the light weight authentication of DNS
messages, but increases the size of the messages by at least 70
octets. DNSSEC specifies for computationally expensive message
authentication SIG(0) using a standard public key signature. As only
one TSIG or SIG(0) can be attached to each DNS answer the size
increase of message authentication is not significant, but may still
lead to a truncation.
2.2. IPv6 Motivations
IPv6 addresses [RFC 2874] are 128 bits and can be represented in the
DNS by multiple A6 records, each consisting of a domain name and a
bit field. The domain name refers to an address prefix that may
require additional A6 RRs to be included in the answer. Answers
where the queried name has multiple A6 addresses may overflow a 512-
octet UDP packet size.
Gudmundsson Standards Track