Deprecating the Use of Router Alert in LSP Ping
draft-ietf-mpls-lspping-norao-08

MPLS WG                                                      K. Kompella
Internet-Draft                                                 R. Bonica
Updates: 8029 (if approved)                             Juniper Networks
Intended status: Standards Track                          G. Mirsky, Ed.
Expires: 2 September 2024                                       Ericsson
                                                            1 March 2024

            Deprecating the Use of Router Alert in LSP Ping
                    draft-ietf-mpls-lspping-norao-08

Abstract

   The MPLS echo request and MPLS echo response messages, defined in RFC
   8029 "Detecting Multiprotocol Label Switched (MPLS) Data-Plane
   Failures" (usually referred to as LSP ping messages), are
   encapsulated in IP whose headers include a Router Alert Option (RAO).
   In actual deployments, the RAO was neither required nor used.
   Furthermore, RFC 6398 identifies security vulnerabilities associated
   with the RAO in non-controlled environments, e.g., the case of using
   the MPLS echo request/reply as inter-area Operations, Administration,
   and Maintenance (OAM), and recommends against its use outside of
   controlled environments.

   Therefore, this document retires the RAO for MPLS OAM and updates RFC
   8029 to remove the RAO from LSP ping message encapsulations.
   Furthermore, this document explains why RFC 7506 has been
   reclassified as Historic.

   Also, the use of an IPv6 loopback address (::1/128) as the IPv6
   destination address for an MPLS echo request message is RECOMMENDED.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 2 September 2024.

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Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Note for the RFC Editor . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Router Alert for LSP Ping (RFC 8029)  . . . . . . . . . . . .   3
     3.1.  MPLS Echo Request . . . . . . . . . . . . . . . . . . . .   4
     3.2.  MPLS Echo Reply . . . . . . . . . . . . . . . . . . . . .   4
   4.  Reclassification of RFC 7506 as Historic  . . . . . . . . . .   5
   5.  Update to RFC 8029  . . . . . . . . . . . . . . . . . . . . .   5
   6.  Backwards Compatibility . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   8
   11. Informational References  . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Note for the RFC Editor

   Per IESG decision, this document MUST be processed only after the
   status of RFC 7506 is changed to Historical.  This note must be
   removed before the publication.

2.  Introduction

   RFC 8029 - "Detecting Multiprotocol Label Switched (MPLS) Data-Plane
   Failures" (usually referred to as 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
   checks LSP connectivity.  When operating in traceroute mode, it can
   trace an LSP and localize failures to a particular node along an LSP.

   The reader is assumed be familiar with [RFC8029] and its terminology.

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   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 MPLS echo request
   message is further encapsulated in an MPLS label stack, except when
   all of the Forwarding Equivalency Classes in the stack correspond to
   Implicit Null labels.

   When operating in ping mode, LSP ping sends a single MPLS echo
   request message, with the MPLS TTL set to 255.  This message is
   intended to reach the egress Label Switching Router (LSR).  When
   operating in traceroute mode, MPLS ping sends multiple MPLS echo
   request messages as defined in Section 4.3 of [RFC8029].  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.

   According to [RFC8029], the IP header that encapsulates an MPLS echo
   request message must include a Router Alert Option (RAO).
   Furthermore, [RFC8029] also says that the IP header that encapsulates
   an MPLS echo reply message must include an RAO if the value of the
   Reply Mode in the corresponding MPLS echo request message is "Reply
   via an IPv4/IPv6 UDP packet with Router Alert".  This document
   explains why RAO was not needed in both cases.  Furthermore,
   [RFC6398] identifies security vulnerabilities associated with the RAO
   in non-controlled environments, e.g., the case of using the MPLS echo
   request/reply as inter-domain OAM over the public Internet, and
   recommends against its use outside of controlled environments, e.g.,
   outside a single administrative domain.

   Therefore, this document updates RFC 8029 [RFC8029] to retire the RAO
   from both LSP ping message encapsulations and explains why RFC 7506
   [RFC7506] has been reclassified as Historic.

2.1.  Requirements Language

   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.

3.  Router Alert for LSP Ping (RFC 8029)

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3.1.  MPLS 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, a set of the mechanisms that are used
   concurrently to prevent leaking MPLS echo request messages has been
   defined in [RFC8029]:

   1.  When the MPLS echo request message is encapsulated in IPv4, the
       IPv4 destination address must be chosen from the subnet 127/8.
       When the MPLS 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 MPLS echo request message is encapsulated in IPv4, the
       IPv4 TTL must be equal to 1.  When the MPLS echo request message
       is encapsulated in IPv6, the IPv6 Hop Limit must be equal to 1.
       For further information on the encoding of the TTL/Hop Limit in
       an MPLS echo request message, see Section 4.3 of [RFC8029].

   3.  When the MPLS echo request message is encapsulated in IPv4, the
       IPv4 header must include an RAO with the option value set to
       "Router shall examine packet" [RFC2113].  When the MPLS 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 with the option value set to
       MPLS OAM [RFC7506].

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

   Therefore, this document updates RFC 8029 [RFC8029] in that
   Requirement 3 is removed.

   No implementation that relies on the RAO to prevent packets from
   being forwarded beyond the egress LSR have been reported to the MPLS
   working group.

3.2.  MPLS Echo Reply

   An LSP ping replies to the MPLS echo request message with an MPLS
   echo reply message.  Four reply modes are defined in [RFC8029]:

   1.  Do not reply

   2.  Reply via an IPv4/IPv6 UDP packet

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   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 [RFC8029], "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 updates RFC 8029 [RFC8029] in that
   mode 3 is removed.

   No implementations of mode 3 have been reported to the MPLS working
   group.

4.  Reclassification of RFC 7506 as Historic

   RFC 7506 [RFC7506] defines the IPv6 Router Alert Option for MPLS
   Operations, Administration, and Management.  This document explains
   why RFC 7506 [RFC7506] has been reclassified as Historic.

5.  Update to RFC 8029

   [RFC8029] requires that the IPv6 Destination Address used in IP/UDP
   encapsulation of an MPLS 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 MPLS
   echo request message as follows:

   OLD

   The 127/8 range for IPv4 and that same range embedded in an
   IPv4-mapped IPv6 address for IPv6 was chosen for a number of reasons.

   RFC 1122 allocates the 127/8 as the "Internal host loopback address"
   and states: "Addresses of this form MUST NOT appear outside a host."
   Thus, the default behavior of hosts is to discard such packets.  This
   helps to ensure that if a diagnostic packet is misdirected to a host,
   it will be silently discarded.

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   RFC 1812 [RFC1812] states:

   *  A router SHOULD NOT forward, except over a loopback interface, any
      packet that has a destination address on network 127.  A router
      MAY have a switch that allows the network manager to disable these
      checks.  If such a switch is provided, it MUST default to
      performing the checks.

   This helps to ensure that diagnostic packets are never IP forwarded.

   The 127/8 address range provides 16M addresses allowing wide
   flexibility in varying addresses to exercise ECMP paths.  Finally, as
   an implementation optimization, the 127/8 range provides an easy
   means of identifying possible LSP packets.

   NEW

   The 127/8 range for IPv4 was chosen for a number of reasons.

   RFC 1122 [RFC1122] allocates the 127/8 as the "Internal host loopback
   address" and states: "Addresses of this form MUST NOT appear outside
   a host."  Thus, the default behavior of hosts is to discard such
   packets.  This helps to ensure that if a diagnostic packet is
   misdirected to a host, it will be silently discarded.

   RFC 1812 [RFC1812] states:

   *  A router SHOULD NOT forward, except over a loopback interface, any
      packet that has a destination address on network 127.  A router
      MAY have a switch that allows the network manager to disable these
      checks.  If such a switch is provided, it MUST default to
      performing the checks.

   This helps to ensure that diagnostic packets are never IP forwarded.

   The 127/8 address range provides 16M addresses allowing wide
   flexibility in varying addresses to exercise ECMP paths.  Finally, as
   an implementation optimization, the 127/8 range provides an easy
   means of identifying possible LSP packets.

   The IPv6 destination address for an MPLS echo request message is
   selected as follows:

   *  The IPv6 loopback address ::1/128 SHOULD be used.

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

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   *  To exercise all paths in an ECMP environment, the source of
      entropy other than the IP destination address SHOULD be used.  For
      example, MPLS Entropy Label [RFC6790] or IPv6 Flow Label [RFC6438]
      can be used as the source of entropy.

   END

   Additionally, this specification updates Section 2.2 of [RFC8029] to
   replace the whole of the section with the following text:

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

   Resulting from the removal of the Reply mode 3 "Reply via an IPv4/
   IPv6 UDP packet with Router Alert" (see Section 3.2), this
   specification updates Section 4.5 of [RFC8029] by removing the
   following text:

      If the Reply Mode in the echo request is "Reply via an IPv4 UDP
      packet with Router Alert", then the IP header MUST contain the
      Router Alert IP Option of value 0x0 [RFC2113] for IPv4 or 69
      [RFC7506] for IPv6.  If the reply is sent over an LSP, the topmost
      label MUST in this case be the Router Alert label (1) (see
      [RFC3032]).

   Furthermore, this specification updates Section 4.3 of [RFC8029] as
   follows:

   OLD:

   The Router Alert IP Option of value 0x0 [RFC2113] for IPv4 or value
   69 [RFC7506] for IPv6 MUST be set in the IP header.

   NEW:

   The Router Alert IP Option of value 0x0 [RFC2113] for IPv4 or value
   69 [RFC7506] for IPv6 MUST NOT be set in the IP header.

   END

6.  Backwards Compatibility

   LSP Ping implementations that conform to this specification SHOULD
   ignore RAO options when they arrive on incoming MPLS echo request and
   MPLS echo reply messages.  However, this will not harm backwards
   compatibility because other mechanisms will also be in use by all
   legacy implementations in the messages they send and receive.

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   Section 7 of this document deprecates the IPv6 RAO value for MPLS OAM
   (69) in [IANA-IPV6-RAO] and the Reply Mode 3 ("Reply via an IPv4/IPv6
   UDP packet with Router Alert") in [IANA-LSP-PING].

   [RFC8126] offers a formal description of the word "Deprecated".  In
   this context, "Deprecated" means that the deprecated values SHOULD
   NOT be used in new implementations, and that deployed implementations
   that already use these values continue to work seamlessly.

7.  IANA Considerations

   IANA is requested to mark the IPv6 RAO value of MPLS OAM (69) in
   [IANA-IPV6-RAO] as "Deprecated".

   IANA is also requested to mark Reply Mode 3 ("Reply via an IPv4/IPv6
   UDP packet with Router Alert") in "Multiprotocol Label Switching
   (MPLS) Label Switched Paths (LSPs) Ping Parameters"[IANA-LSP-PING] as
   "Deprecated".

8.  Security Considerations

   The recommendations this document makes do not compromise security.
   In case of using IPv6 loopback address ::1/128 strengthens security
   for LSP Ping by using the standardized loopback address with well-
   defined behavior.

9.  Acknowledgments

   The authors express their appreciation to Adrian Farrel and Gyan
   Mishra for their suggestions that improved the readability of the
   document.

10.  Normative References

   [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>.

   [RFC1812]  Baker, F., Ed., "Requirements for IP Version 4 Routers",
              RFC 1812, DOI 10.17487/RFC1812, June 1995,
              <https://www.rfc-editor.org/info/rfc1812>.

   [RFC2113]  Katz, D., "IP Router Alert Option", RFC 2113,
              DOI 10.17487/RFC2113, February 1997,
              <https://www.rfc-editor.org/info/rfc2113>.

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   [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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

11.  Informational References

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

   [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>.

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   [RFC6438]  Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
              for Equal Cost Multipath Routing and Link Aggregation in
              Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
              <https://www.rfc-editor.org/info/rfc6438>.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

Authors' Addresses

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

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

   Greg Mirsky (editor)
   Ericsson
   Email: gregimirsky@gmail.com

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