Deprecating the Use of Router Alert in LSP Ping
draft-kompella-mpls-lspping-norao-01

MPLS WG                                                      K. Kompella
Internet-Draft                                                 R. Bonica
Updates: 7506, 8029 (if approved)                       Juniper Networks
Intended status: Standards Track                               G. Mirsky
Expires: 13 May 2023                                            Ericsson
                                                         9 November 2022

            Deprecating the Use of Router Alert in LSP Ping
                  draft-kompella-mpls-lspping-norao-01

Abstract

   LSP ping messages (RFC 8029) are encapsulated in IP headers that
   include a Router Alert Option (RAO).  The rationale for including an
   RAO is questionable.  Furthermore, RFC6398 identifies security
   vulnerabilities associated with the RAO.

   Therefore, this document removes the RAO from LSP ping message
   encapsulations.  It updates RFCs 7506 and 8029.

   This document also recommends the use of an IPv6 loopback address
   (:::1/128) and discourages the use of an IPv4 loopback address mapped
   to IPv6.

Status of This Memo

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Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Router Alert for LSP Ping (RFC 8029)  . . . . . . . . . . . .   3
     2.1.  Echo Request  . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Echo Reply  . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Update to RFC 7506  . . . . . . . . . . . . . . . . . . . . .   4
   4.  Update to RFC 8029  . . . . . . . . . . . . . . . . . . . . .   5
   5.  Backwards Compatibility . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   LSP ping [RFC8029] detects data-plane failures in MPLS Label Switched
   Paths (LSPs).  It can operate in "ping mode" or "traceroute mode".
   When operating in ping mode, it verifies end-to-end LSP continuity.
   When operating in traceroute mode, it can localize failures to a
   particular node along an LSP.

   LSP ping defines a probe message, called the "MPLS echo request".  It
   also defines a response message, called the "MPLS echo reply".  Both
   messages are encapsulated in UDP and IP.  The echo request message is
   further encapsulated in an MPLS label stack.

   When operating in ping mode, LSP ping sends a single echo request
   message, with the MPLS TTL set to a high value (e.g., 255).  This
   message is intended to reach the egress Label Switching Router (LSR).
   When operating in traceroute mode, MPLS ping sends multiple echo
   request messages.  It manipulates the MPLS TTL so that the first
   message expires on the first LSR along the path and subsequent
   messages expire on subsequent LSRs.

   The IP header that encapsulates an echo request message must include
   a Router Alert Option (RAO), while the IP header that encapsulates an
   echo reply message may include an RAO.  In both cases, the rationale

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   for including an RAO is questionable.  Furthermore, [RFC6398]
   identifies security vulnerabilities associated with the RAO and
   recommends against its use outside of controlled environments.

   Therefore, this document removes the RAO from both LSP ping message
   encapsulations.  It updates RFCs 7506 [RFC7506] and 8029.

1.1.  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
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   LSP:  Label Switched Path

   LSR:  Label Switching Router

   RAO:  Router Alert Option

2.  Router Alert for LSP Ping (RFC 8029)

2.1.  Echo Request

   While the MPLS echo request message must traverse every node in the
   LSP under test, it must not traverse any other node.  Specifically,
   the message must not be forwarded beyond the egress Label Switching
   Router (LSR).

   To achieve this, RFC 8029 proposes the following:

   1.  When the echo request message is encapsulated in IPv4, the IPv4
       destination address must be chosen from the subnet 127/8.  When
       the echo request message is encapsulated in IPv6, the IPv6
       destination address must be chosen from the subnet
       0:0:0:0:0:FFFF:7F00:0/104.

   2.  When the echo request message is encapsulated in IPv4, the IPv4
       TTL must be equal to 1.  When the echo request message is
       encapsulated in IPv6, the IPv6 Hop Limit must be equal to 1.

   3.  When the echo request message is encapsulated in IPv4, the IPv4
       header must include an RAO.  When the echo request message is
       encapsulated in IPv6, the IPv6 header chain must include a Hop-
       by-hop extension header and the Hop-by-hop extension header must
       include an RAO.

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   Currently, ALL of these are required.  However, any one is sufficient
   to prevent forwarding the packet beyond the egress LSR.

   Therefore, this document RECOMMENDS removing Requirement 3 from RFC
   8029.

   The authors are not aware of any implementation that relies on the
   RAO to prevent packets from being forwarded beyond the egress LSR.

2.2.  Echo Reply

   An LSP ping replies to the MPLS echo message with an MPLS echo reply
   message.  It has four reply modes:

   1.  Do not reply

   2.  Reply via an IPv4/IPv6 UDP packet

   3.  Reply via an IPv4/IPv6 UDP packet with Router Alert

   4.  Reply via application-level control channel

   The rationale for mode 3 is questionable, if not wholly misguided.
   According to RFC 8029, "If the normal IP return path is deemed
   unreliable, one may use 3 (Reply via an IPv4/IPv6 UDP packet with
   Router Alert)."

   However, it is not clear that the use of the RAO increases the
   reliability of the return path.  In fact, one can argue it decreases
   the reliability in many instances, due to the additional burden of
   processing the RAO.  This document RECOMMENDS removing mode 3 from
   RFC 8029.

   The authors are not aware of any implementations of mode 3.

3.  Update to RFC 7506

   RFC 7506 defines the IPv6 Router Alert Option for MPLS Operations,
   Administration, and Management.  This document RECOMMENDS that RFC
   7506 be reclassified as Historic.

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4.  Update to RFC 8029

   [RFC8029] requires that the IPv6 Destination Address used in IP/UDP
   encapsulation of an echo request packet is selected from the IPv4
   loopback address range mapped to IPv6.  Such packets do not have the
   same behavior as prescribed in[RFC1122] for an IPv4 loopback
   addressed packet.

   [RFC4291] defines ::1/128 as the single IPv6 loopback address.
   Considering that this specification updates section 2.1 of [RFC8029]
   regarding the selection of an IPv6 destination address for an echo
   request message:

   *  For IPv6, the IPv6 loopback address ::1/128 SHOULD be used.

   *  The sender of an echo request MAY select the IPv6 destination
      address from the 0:0:0:0:0:FFFF:7F00/104 range.

   *  To exercise all paths in an ECMP environment, the entropy other
      than the IP destination address SHOULD be used.

5.  Backwards Compatibility

   LSP Ping implementations SHOULD ignore RAO options when they arrive
   on incoming echo request and echo reply messages.

6.  IANA Considerations

   If this document is approved, mark the IPv6 RAO value of MPLS OAM
   (69) in [IANA-IPV6-RAO] as "Deprecated".

   Also, mark Reply Mode 3 ("Reply via an IPv4/IPv6 UDP packet with
   Router Alert") in [IANA-LSP-PING] as "Deprecated".

7.  Security Considerations

   The recommendations this document makes do not compromise security.

8.  Normative References

   [IANA-IPV6-RAO]
              IANA, "IPv6 Router Alert Option Values", n.d.,
              <https://www.iana.org/assignments/ipv6-routeralert-
              values>.

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   [IANA-LSP-PING]
              IANA, "Multiprotocol Label Switching (MPLS) Label Switched
              Paths (LSPs) Ping Parameters", n.d.,
              <https://www.iana.org/assignments/mpls-lsp-ping-
              parameters/mpls-lsp-ping-parameters.xml>.

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,
              <https://www.rfc-editor.org/info/rfc1122>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC6398]  Le Faucheur, F., Ed., "IP Router Alert Considerations and
              Usage", BCP 168, RFC 6398, DOI 10.17487/RFC6398, October
              2011, <https://www.rfc-editor.org/info/rfc6398>.

   [RFC7506]  Raza, K., Akiya, N., and C. Pignataro, "IPv6 Router Alert
              Option for MPLS Operations, Administration, and
              Maintenance (OAM)", RFC 7506, DOI 10.17487/RFC7506, April
              2015, <https://www.rfc-editor.org/info/rfc7506>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

Authors' Addresses

   Kireeti Kompella
   Juniper Networks
   1133 Innovation Way
   Sunnyvale, CA 94089
   United States
   Email: kireeti.ietf@gmail.com

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   Ron Bonica
   Juniper Networks
   1133 Innovation Way
   Sunnyvale, CA 94089
   United States
   Email: rbonica@juniper.net

   Greg Mirsky
   Ericsson
   Email: gregimirsky@gmail.com

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