Port Randomization in the Network Time Protocol Version 4
draft-gont-ntp-port-randomization-04

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Last updated 2019-08-06
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Network Time Protocol (ntp) Working Group                        F. Gont
Internet-Draft                                                   G. Gont
Updates: rfc5905 (if approved)                              SI6 Networks
Intended status: Standards Track                          August 6, 2019
Expires: February 7, 2020

       Port Randomization in the Network Time Protocol Version 4
                  draft-gont-ntp-port-randomization-04

Abstract

   The Network Time Protocol can operate in several modes.  Some of
   these modes are based on the receipt of unsolicited packets, and
   therefore require the use of a service/well-known port as the local
   port number.  However, in the case of NTP modes where the use of a
   service/well-known port is not required, employing such well-known/
   service port unnecessarily increases the ability of attackers to
   perform blind/off-path attacks.  This document formally updates
   RFC5905, recommending the use of port randomization for those modes
   where use of the NTP service port is not required.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on February 7, 2020.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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Gont & Gont             Expires February 7, 2020                [Page 1]
Internet-Draft           NTP Port Randomization              August 2019

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Considerations About Port Randomization in NTP  . . . . . . .   3
     3.1.  Mitigation Against Off-path Attacks . . . . . . . . . . .   3
     3.2.  Effects on Path Selection . . . . . . . . . . . . . . . .   4
     3.3.  Filtering of NTP traffic  . . . . . . . . . . . . . . . .   4
     3.4.  Effect on NAT devices . . . . . . . . . . . . . . . . . .   5
     3.5.  Relation to Other Mitigations for Off-Path Attacks  . . .   5
   4.  Update to RFC5905 . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Possible Future Work  . . . . . . . . . . . . . . . . . . . .   6
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The Network Time Protocol (NTP) is one of the oldest Internet
   protocols, and currently specified in [RFC5905].  Since its original
   implementation, standardization, and deployment, a number of
   vulnerabilities have been found both in the NTP specification and in
   some of its implementations [NTP-VULN].  Some of these
   vulnerabilities allow for off-path/blind attacks, where an attacker
   can send forged packets to one or both NTP peers for achieving Denial
   of Service (DoS), time-shifts, and other undesirable outcomes.  Many
   of these attacks require the attacker to guess or know at least a
   target NTP association, typically identified by the tuple {srcaddr,
   srcport, dstaddr, dstport, keyid}. Some of these parameters may be
   easily known or guessed.

   NTP can operate in several modes.  Some of these modes rely on the
   ability of nodes to receive unsolicited packets, and therefore
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