Avoid IP fragmentation in DNS
draft-fujiwara-dnsop-avoid-fragmentation-00

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Network Working Group                                        K. Fujiwara
Internet-Draft                                                      JPRS
Intended status: Best Current Practice                     July 04, 2019
Expires: January 5, 2020

                     Avoid IP fragmentation in DNS
              draft-fujiwara-dnsop-avoid-fragmentation-00

Abstract

   Path MTU discovery is vulnerable and IP fragmentation may cause
   protocol weakness.  Currently, DNS is said to be the biggest user of
   IP fragmentation.  However, it is possible to avoid IP fragmentation
   in DNS because TCP transport and truncation work well.  This document
   proposes to avoid IP fragmentation in DNS.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 5, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Proposal to avoid IP fragmentation in DNS . . . . . . . . . .   3
   4.  Incremental deployment  . . . . . . . . . . . . . . . . . . .   3
   5.  Considerations  . . . . . . . . . . . . . . . . . . . . . . .   3
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   DNS has EDNS0 [RFC6891] mechanism.  It enables that DNS server can
   send large size response using UDP.  Now EDNS0 is widely deployed,
   then DNS is said to be the biggest user of IP fragmentation.

   However, "Fragmentation Considered Poisonous" [Herzberg2013] proposed
   effective off-path DNS cache poisoning attack vectors using IP
   fragmentation.  "IP fragmentation attack on DNS" [Hlavacek2013] and
   "Domain Validation++ For MitM-Resilient PKI" [Brandt2018] proposed
   that off-path attackers can intervene in path MTU discovery [RFC1191]
   to perform intentionally fragmented responses from authoritative
   servers.  [RFC7739] stated security implications of predictable
   fragment identification values.

   As a result, we cannot trust fragmented UDP packets and path MTU
   discovery.  By the way, TCP is considered resistant against IP
   fragmentation attacks because TCP has sequence number and
   acknowledgement number in each sequence.

   This document proposes to avoid IP fragmentation in DNS.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   Many of the specialized terms used in this document are defined in
   DNS Terminology [RFC8499].

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3.  Proposal to avoid IP fragmentation in DNS

   The methods to avoid IP fragmentation in DNS are described below:

   o  Full-service resolvers SHOULD set EDNS0 requestor's UDP payload
      size to 1220.  (defined in [RFC4035] as minimum payload size)

   o  Authoritative servers and full-service resolvers SHOULD choose