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UDP Return Path for Packet Loss and Delay Measurement for MPLS Networks

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7876.
Authors Stewart Bryant , Siva Sivabalan , Sagar Soni
Last updated 2016-07-26 (Latest revision 2016-04-07)
Replaces draft-ietf-mpls-pm-udp-return
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Associated WG milestone
May 2015
Submit draft-ietf-mpls-rfc6374-udp-return-path for publicatiion
Document shepherd Loa Andersson
Shepherd write-up Show Last changed 2015-10-21
IESG IESG state Became RFC 7876 (Proposed Standard)
Action Holders
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Deborah Brungard
Send notices to (None)
IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack
MPLS                                                           S. Bryant
Internet-Draft                                               Independent
Intended status: Standards Track                            S. Sivabalan
Expires: October 9, 2016                                         S. Soni
                                                           Cisco Systems
                                                           April 7, 2016

                        RFC6374 UDP Return Path


   RFC6374 defines a protocol for Packet Loss and Delay Measurement for
   MPLS networks (MPLS-PLDM).  This document specifies the procedures to
   be used when sending and processing out-of-band MPLS performance
   management responses over an IP/UDP return path.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 9, 2016.

Copyright Notice

   Copyright (c) 2016 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
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

1.  Introduction

   This document describes how Packet Loss and Delay Measurement for
   MPLS Networks protocol (MPLS-PLDM) [RFC6374] out-of-band responses
   can be delivered to the querier using UDP/IP.

   The use of UDP may be required to support data path management such
   as passage through firewalls, or to provide the necessary
   multiplexing needed in bistatic operation where the querier and the
   collector are not co-located and the collector is gathering the
   response information for a number of responders.  In a highly scaled
   system some MPLS-PLDM sessions may be off-loaded to a specific node
   within the distributed system that comprises the Label Switching
   Router (LSR) as a whole.  In such systems the response may arrive via
   any interface in the LSR and need to be forwarded internally to the
   processor tasked with handling the particular MPLS-PLDM measurement.
   Currently the MPLS-PLDM protocol does not have any mechanism to
   deliver the PLDM Response message to a particular node within a
   multi-CPU LSR.

   The procedure described in this specification describes how the
   querier requests delivery of the MPLS-PLDM response over IP to a
   dynamic UDP port.  It makes no other changes to the protocol and thus
   does not affect the case where the response is delivered over a MPLS
   Associated Channel [RFC5586].

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Solution Overview

   This document specifies that, unless configured otherwise, if a UDP
   Return Object (URO) is present in a MPLS-PLDM Query, the responder
   SHOULD use the IP address and UDP port in the URO to reply back to
   the querier.  The querier MAY include multiple UROs in a MPLS-PLDM
   Query indicating to the responder that an identical responses SHOULD
   be sent to each address-port pair.  A responder MAY be designed or
   configured to only transmit a single response, in which case the
   response MUST be sent using the parameters specified in the first URO
   in the query packet that it is able to use (see Section 4.3).

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   The procedures defined in this document may be applied to both
   unidirectional and bidirectional LSPs.  In this document, the term
   bidirectional LSP includes the co-routed bidirectional LSP defined in
   [RFC3945] and the associated bidirectional LSP that is constructed
   from a pair of unidirectional LSPs (one for each direction) that are
   associated with one another at the LSP's ingress/egress points
   [RFC5654].  The mechanisms defined in this document can apply to both
   IP/MPLS and to the MPLS Transport Profile (MPLS-TP)[RFC5654],

3.1.  UDP Return Object

   NOTE TO RFC Editor please delete the following paragraph before


   Note to reviewers - We considered a number of approaches to the
   design.  The first was to use the existing address object and a
   separate UDP object, but concern was expressed in the WG that there
   may be more than one collector that required this information, and
   the combined size of the two objects was large.  The next approach
   considered by the authors was to create a new object by appending a
   UDP port to the existing generalized address object.  However, noting
   that UDP is only likely to be sent over IP and that it will be a long
   time before we design a third major version of IP we can compress the
   object either by having separate IPv4 and IPv6 objects, or using the
   address length as the discriminator.  The object design below uses
   the latter approach.  The resultant combined UDP port + address
   object is thus the same size as the original address object.


   The format of the UDP Return Object (URO) is as follows:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      | URO TLV Type  | Length={6,18} |    UDP-Destination-Port       |
      ~                           Address                             ~

   The Type and Length fields are each 8 bits long.  The Length field
   indicates the size in bytes of the remainder of the object (i.e. is
   the size of the address in bytes plus 2).  When the address is IPv4
   the length field is thus 6 and when the address is IPv6 the length

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   field is thus 18.  The length field therefore acts as both the TLV
   parsing parameter and the address family type indicator.

   The UDP Return Object Type (URO TLV Type) has a value of 131.

   The UDP Destination Port is a UDP Destination port as specified in

   The Address is either an IPv4 or an IPv6 address.

   The URO MUST NOT appear in a response and MUST be ignored if it is
   found to be present.

   To prevent any ambiguity as to which address the responder needs to
   reply to, an MPLS-PLDM Query message containing a URO MUST NOT
   include an RFC6374 Return Address TLV (TLV 1).  Additionally, the
   method of constructing the return address from the Source Address TLV
   (TLV 130) described in Section 3.5.2 of RFC6374 MUST NOT be used to
   construct a Response to a Query message that contains a URO.

4.  Theory of Operation

   This document defines the UDP Return Object to enable the MPLS-PLDM
   querier to specify the return path for the MPLS-PLDM reply using UDP/
   IP encapsulation.

   When the MPLS-PLDM Response is requested out-of-band by setting the
   Control Code of the MPLS-PLDM query to "Out-of-band Response
   Requested", and the URO is present, the responder SHOULD send the
   response back to querier on the specified destination UDP port at the
   specified destination IP address contained in the URO.

   If the URO is expected but is not present in a query message and an
   MPLS-PLDM Response is requested out-of-band, the query message MUST
   NOT be processed further, and if possible an "Error - Invalid
   Message" ([RFC6374] Section 3.1) SHOULD be send to the querier and
   the operator notified via the management system (see Section 4.2 for
   further details.

4.1.  Sending an MPLS-PLDM Query

   When sending an MPLS-PLDM query message, in addition to the rules and
   procedures defined in [RFC6374]; the Control Code of the MPLS-PLDM
   query MUST be set to "Out-of-band Response Requested", and a URO MUST
   be carried in the MPLS-PLDM query message.

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   If the querier uses the UDP port to de-multiplex the response for
   different measurement type, there MUST be a different UDP port for
   each measurement type (Delay, loss and delay-loss combined).

   An implementation MAY use multiple UDP ports for same measurement
   type to direct the response to the correct management process in the

4.2.  Receiving an MPLS PLDM Query Request

   The processing of MPLS-PLDM query messages as defined in [RFC6374]
   applies in this document.  In addition, when an MPLS-PLDM query
   message is received, with the control code of the MPLS-PLDM query set
   to "Out-of-band Response Requested" with a URO present, then the
   responder SHOULD use that IP address and UDP port to send MPLS-PLDM
   response back to querier.

   If an Out-of-band response is requested and the URO is missing, the
   query SHOULD be dropped in the case of a unidirectional LSP.  If the
   TLV is missing on a bidirectional LSP, the control code of the
   Response message SHOULD set to 0x1C indicating "Error - Invalid
   Message" ([RFC6374] Section 3.1) and the response SHOULD be sent over
   the reverse LSP.  The receipt of such a mal-formed request SHOULD be
   notified to the operator through the management system, taking the
   normal precautions with respect to the prevention of overload of the
   error reporting system.

4.3.  Sending an MPLS-PLDM Response

   As specified in [RFC6374] the MPLS-PLDM Response can be sent over
   either the reverse MPLS LSP for a bidirectional LSP or over an IP
   path.  It MUST NOT be sent other than in response to an MPLS-PLDM
   query message.

   When the requested return path is an IP forwarding path and this
   method is in use, the destination IP address and UDP port is copied
   from the URO.  The source IP address and the source UDP Port of the
   Response packet is left to discretion of the responder subject to the
   normal management and security considerations.  If the querier has
   included URO(s) for only one IP address family and a return path of
   that type is not available, then the query message MUST be discarded,
   and the operator SHOULD be informed of the error through the
   management system using the normal rate limited approach.  If the
   responder is configured to only respond with a single response, and a
   path using the IP address family in the first URO is not available,
   the responder MAY search the UROs for the first URO specifying a
   return address family for which it does have a path and use the
   parameters in that URO to respond.  If the responder is designed or

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   configured not to search for a URO that it can respond to, then the
   operator SHOULD be informed of the error through the management
   system using the normal rate limited approach.

   The packet format for the MPLS-PLDM response after the UDP header is
   as specified in [RFC6374].  As shown in Figure 1 the Associate
   Channel Header (ACH) [RFC5586] is not included.  The information
   provided by the ACH is not needed since the correct binding between
   the query and response messages is achieved though the UDP Port and
   the session indentifier contained in the RFC6374 message.

       |  IP Header                                               |
       .    Source Address = Responders IP Address                |
       .    Destination Address = URO.Address                     |
       .    Protocol = UDP                                        .
       .                                                          .
       | UDP Header                                               |
       .   Source Port = As chosen by Responder                   .
       .   Destination Port = URO.UDP-Destination-Port            .
       .                                                          .
       | Message as specified in RFC6374                          |
       .                                                          .

                     Figure 1: Response packet Format

   If the return path is an IP path, only one-way delay or one-way loss
   measurement can be carried out.  In this case timestamps 3 and 4 MUST
   be zero as specified in [RFC6374].

4.4.  Receiving an MPLS-PLDM Response

   If the response was received over UDP/IP and an out-of-band response
   was expected, the Response message SHOULD be directed to the
   appropriate measurement process as determined by the destination UDP
   Port, and processed using the corresponding measurement type
   procedure specified in F [RFC6374].

   If the Response was received over UDP/IP and an out-of-band response
   was not requested, that response SHOULD be dropped and the event
   SHOULD be notified to the operator through the management system,
   taking the normal precautions with respect to the prevention of
   overload of the error reporting system.

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5.  Congestion Considerations

   This protocol MUST be run in accordance the guidance provided in
   [RFC5405].  As advised in section 3.2.1 of RFC5405, operators that
   wish to run this protocol at rates in excess of one packet per three
   seconds need to ensure that the MPLS path being monitored and any IP
   path that may be used to carry the response are provisioned such that
   there is a negligible chance of this protocol causing congestion.
   Additionally, if a significant number of response packets are lost,
   the querier MUST reduce the sending rate to a point where there is a
   negligible chance that this protocol is contributing to network
   congestion.  The operator should also take precautions that response
   packets do not leak out of the network domain being used and cause
   congestion elsewhere.  If a default IP address is configured by the
   equipment vendor, this MUST be an address known to contain the
   response packet within the responder, such as the IPv4 localhost
   address [RFC6890] or the IPv6 loopback address [RFC4291].  A
   responder receiving a query specifying this as a return address, and
   not being configured to expect such a return address*, SHOULD notify
   the operator in a suitably rate limited manner.

6.  Manageability Considerations

   The manageability considerations described in Section 7 of [RFC6374]
   are applicable to this specification.  Additional manageability
   considerations are noted within the elements of procedure of this

   Nothing in this document precludes the use of a configured UDP/IP
   return path in a deployment in which configuration is preferred to
   signalling.  In these circumstances the URO MAY be omitted from the
   MPLS-PLDM messages.

7.  Security Considerations

   The MPLS-PLDM system is not intended to be deployed on the public
   Internet.  It is intended for deployment in well managed private and
   service provider networks.  The security considerations described in
   Section 8 of [RFC6374] are applicable to this specification and the
   reader's attention is drawn to the last two paragraphs.
   Cryptographic measures may be enhanced by the correct configuration
   of access control lists and firewalls.

   To prevent the use of this protocol as a reflection attack vector,
   the operator should ensure that the IP address in the URO addresses a
   system that is expecting to act as a receiver of PLDM responses.

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   There is no additional exposure of information to pervasive
   monitoring systems observing LSPs that are being monitored.

8.  IANA Considerations

   IANA has made an early allocation of a new Optional TLV type from
   MPLS Loss/Delay Measurement TLV Object Registry contained within the
   Generic Associated Channel (G-ACh) Parameters registry set.  IANA is
   requested to modify the description text as shown below.

      Code              Description            Reference
       131     UDP Return                  [This]

9.  Acknowledgements

   We acknowledge the contribution of Joseph Chin and Rakesh Gandhi,
   both with Cisco Systems.  We thank Loa Andersson, Eric Osborne,
   Mustapha Aissaoui, Jeffrey Zhang and Ross Callon for their review

   We thank all who have reviewed this text and provided feedback.

10.  References

10.1.  Normative References

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3945]  Mannie, E., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Architecture", RFC 3945,
              DOI 10.17487/RFC3945, October 2004,

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <>.

   [RFC5405]  Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
              for Application Designers", BCP 145, RFC 5405,
              DOI 10.17487/RFC5405, November 2008,

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   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,

   [RFC5654]  Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
              Sprecher, N., and S. Ueno, "Requirements of an MPLS
              Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
              September 2009, <>.

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374,
              DOI 10.17487/RFC6374, September 2011,

   [RFC6890]  Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
              "Special-Purpose IP Address Registries", BCP 153,
              RFC 6890, DOI 10.17487/RFC6890, April 2013,

10.2.  Informative References

   [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
              L., and L. Berger, "A Framework for MPLS in Transport
              Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010,

Authors' Addresses

   Stewart Bryant


   Siva Sivabalan
   Cisco Systems


   Sagar Soni
   Cisco Systems


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