Network Working Group Y. Morishita
Request for Comments: 4074 JPRS
Category: Informational T. Jinmei
Toshiba
May 2005
Common Misbehavior Against DNS Queries for IPv6 Addresses
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
There is some known misbehavior of DNS authoritative servers when
they are queried for AAAA resource records. Such behavior can block
IPv4 communication that should actually be available, cause a
significant delay in name resolution, or even make a denial of
service attack. This memo describes details of known cases and
discusses their effects.
1. Introduction
Many existing DNS clients (resolvers) that support IPv6 first search
for AAAA Resource Records (RRs) of a target host name, and then for A
RRs of the same name. This fallback mechanism is based on the DNS
specifications, which if not obeyed by authoritative servers, can
produce unpleasant results. In some cases, for example, a web
browser fails to connect to a web server it could otherwise reach.
In the following sections, this memo describes some typical cases of
such misbehavior and its (bad) effects.
Note that the misbehavior is not specific to AAAA RRs. In fact, all
known examples also apply to the cases of queries for MX, NS, and SOA
RRs. The authors believe this can be generalized for all types of
queries other than those for A RRs. In this memo, however, we
concentrate on the case for AAAA queries, since the problem is
particularly severe for resolvers that support IPv6, which thus
affects many end users. Resolvers at end users normally send A
and/or AAAA queries only, so the problem for the other cases is
relatively minor.
2. Network Model
In this memo, we assume a typical network model of name resolution
environment using DNS. It consists of three components: stub
resolvers, caching servers, and authoritative servers. A stub
resolver issues a recursive query to a caching server, which then
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