Port Randomization in the Network Time Protocol Version 4
draft-ietf-ntp-port-randomization-06

Document Type Active Internet-Draft (ntp WG)
Last updated 2020-09-15
Replaces draft-gont-ntp-port-randomization
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Network Time Protocol (ntp) Working Group                        F. Gont
Internet-Draft                                                   G. Gont
Updates: 5905 (if approved)                                 SI6 Networks
Intended status: Standards Track                              M. Lichvar
Expires: March 19, 2021                                          Red Hat
                                                      September 15, 2020

       Port Randomization in the Network Time Protocol Version 4
                  draft-ietf-ntp-port-randomization-06

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 well-known port as the local port
   number.  However, in the case of NTP modes where the use of a well-
   known port is not required, employing such well-known port
   unnecessarily increases the ability of attackers to perform blind/
   off-path attacks.  This document formally updates RFC5905,
   recommending the use of transport-protocol ephemeral port
   randomization for those modes where use of the NTP well-known port is
   not required.

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 March 19, 2021.

Copyright Notice

   Copyright (c) 2020 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
   Provisions Relating to IETF Documents

Gont, et al.             Expires March 19, 2021                 [Page 1]
Internet-Draft           NTP Port Randomization           September 2020

   (https://trustee.ietf.org/license-info) in effect on the date of
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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.  Implementation Status . . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   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, or 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} (see section 9.1 of [RFC5905]).
   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
   require the use of the NTP well-known port (123).  However, for modes
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