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Internet Engineering Task Force (IETF)                      C. PignataroRequest for Comments: 7881                                       D. WardCategory: Standards Track                                          CiscoISSN: 2070-1721                                                 N. Akiya                                                     Big Switch Networks                                                               July 2016Seamless Bidirectional Forwarding Detection (S-BFD)for IPv4, IPv6, and MPLSAbstract   This document defines procedures for using Seamless Bidirectional   Forwarding Detection (S-BFD) in IPv4, IPv6, and MPLS environments.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7881.Copyright Notice   Copyright (c) 2016 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) 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   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Pignataro, et al.            Standards Track                    [Page 1]

RFC 7881          Seamless BFD for IPv4, IPv6, and MPLS        July 2016Table of Contents1. Introduction ....................................................22. S-BFD UDP Port ..................................................23. S-BFD Echo UDP Port .............................................34. S-BFD Control Packet Demultiplexing .............................35. Initiator Procedures ............................................35.1. Details of S-BFD Control Packets Sent by SBFDInitiator .....45.1.1. Target versus Remote Entity (S-BFD Discriminator) ...46. Responder Procedures ............................................56.1. Details of S-BFD Control Packets Sent by SBFDReflector .....57. Security Considerations .........................................68. IANA Considerations .............................................69. References ......................................................79.1. Normative References .......................................79.2. Informative References .....................................7   Acknowledgements ...................................................8   Contributors .......................................................8   Authors' Addresses .................................................81.  Introduction   Seamless Bidirectional Forwarding Detection (S-BFD) [RFC7880] defines   a generalized mechanism to allow network nodes to seamlessly perform   continuity checks to remote entities.  This document defines   necessary procedures for using S-BFD in IPv4, IPv6, and MPLS   environments.   The reader is expected to be familiar with the IP [RFC791] [RFC2460],   BFD [RFC5880], MPLS BFD [RFC5884], and S-BFD [RFC7880] terms and   protocol constructs.   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [RFC2119].2.  S-BFD UDP Port   A new UDP port is defined for use by S-BFD in IPv4, IPv6, and MPLS   environments: 7784.   In S-BFD Control packets from the SBFDInitiator to the SBFDReflector,   the SBFDReflector session MUST listen for incoming S-BFD Control   packets on port 7784.  SBFDInitiator sessions MUST transmit S-BFD   Control packets with destination port 7784.  The source port of the   S-BFD Control packets transmitted by SBFDInitiator sessions can be   any port, with one exception: it MUST NOT be 7784.  The same UDPPignataro, et al.            Standards Track                    [Page 2]

RFC 7881          Seamless BFD for IPv4, IPv6, and MPLS        July 2016   source port number MUST be used for all S-BFD Control packets   associated with a particular SBFDInitiator session.  The source port   number is unique among all SBFDInitiator sessions on the system.   In S-BFD Control packets from the SBFDReflector to the SBFDInitiator,   the SBFDInitiator session MUST listen for reflected S-BFD Control   packets at its source port.3.  S-BFD Echo UDP Port   The BFD Echo port defined by [RFC5881], port 3785, is used for the   S-BFD Echo function in IPv4, IPv6, and MPLS environments.   SBFDInitiator sessions MUST transmit S-BFD Echo packets with   destination port 3785.  The setting of the UDP source port [RFC5881]   and the procedures [RFC7880] for the S-BFD Echo function are outside   the scope of this document.4.  S-BFD Control Packet Demultiplexing   S-BFD Control packet demultiplexing follows the procedure specified   inSection 7.1 of [RFC7880].  A received S-BFD Control packet MUST be   demultiplexed with the destination UDP port field.   This procedure for an S-BFD packet is executed on both the initiator   and the reflector.  If the port is 7784 (i.e., an S-BFD packet for   the SBFDReflector), then the packet MUST be looked up to locate a   corresponding SBFDReflector session based on the value from the   Your Discriminator field in the table describing S-BFD   Discriminators.  If the port is not 7784 but the packet is   demultiplexed to be for an SBFDInitiator, then the packet MUST be   looked up to locate a corresponding SBFDInitiator session based on   the value from the Your Discriminator field in the table describing   BFD Discriminators.  In that case, the destination IP address of the   packet SHOULD be validated to be for itself.  If the packet   demultiplexes to a classical BFD session, then the procedures from   [RFC5880] apply.5.  Initiator Procedures   S-BFD Control packets are transmitted with an IP header, UDP header,   and BFD Control packet ([RFC5880]).  When S-BFD Control packets are   explicitly label switched (i.e., not IP routed and forwarded over a   Label Switched Path (LSP), but explicitly sent on a specific LSP),   the former is prepended with a label stack.  Note that this document   does not make a distinction between a single-hop S-BFD scenario and a   multi-hop S-BFD scenario; both scenarios are supported.Pignataro, et al.            Standards Track                    [Page 3]

RFC 7881          Seamless BFD for IPv4, IPv6, and MPLS        July 2016   The necessary values in the BFD control headers are described in   [RFC7880].Section 5.1 describes necessary values in the MPLS   header, IP header, and UDP header when an SBFDInitiator on the   initiator is sending S-BFD Control packets.5.1.  Details of S-BFD Control Packets Sent by SBFDInitiator   o  Specifications common to both IP-routed S-BFD Control packets and      explicitly label-switched S-BFD Control packets:      *  The Source IP Address field of the IP header MUST be set to a         local IP address that is expected to be routable by the target         (i.e., not an IPv6 link-local address when the target is         multiple hops away).      *  The UDP destination port MUST be set to a well-known UDP         destination port assigned for S-BFD, i.e., 7784.      *  The UDP source port MUST NOT be set to 7784.   o  Specifications for IP-routed S-BFD Control packets:      *  The Destination IP Address field of the IP header MUST be set         to an IP address of the target.      *  The TTL / Hop Limit field of the IP header SHOULD be set         to 255.   o  Specifications for explicitly label-switched S-BFD Control      packets:      *  S-BFD Control packets MUST have the label stack that is         expected to reach the target.      *  The TTL field of the topmost label SHOULD be 255.      *  The destination IP address MUST be chosen from the 127/8 range         for IPv4 and from the 0:0:0:0:0:ffff:7f00:0/104 range for IPv6,         as per [RFC5884].      *  The TTL / Hop Limit field of the IP header MUST be set to 1.5.1.1.  Target versus Remote Entity (S-BFD Discriminator)   Typically, an S-BFD Control packet will have the Your Discriminator   field corresponding to an S-BFD Discriminator of the remote entity   located on the target network node defined by the destination IP   address or the label stack.  It is, however, possible for anPignataro, et al.            Standards Track                    [Page 4]

RFC 7881          Seamless BFD for IPv4, IPv6, and MPLS        July 2016   SBFDInitiator to carefully set the Your Discriminator and TTL fields   to perform a continuity test in the direction towards a target, but   destined to a transit network node and not to the target itself.Section 5.1 intentionally uses the word "target" instead of "remote   entity" to accommodate this possible S-BFD usage through TTL expiry.   This also requires that S-BFD Control packets not be dropped by the   responder node due to TTL expiry.  Thus, implementations on the   responder MUST allow received S-BFD Control packets taking a TTL   expiry exception path to reach the corresponding SBFDReflector   session.  This is an existing packet-processing exception practice   for Operations, Administration, and Maintenance (OAM) packets, where   the control plane further identifies the type of OAM by the protocol   and port numbers.6.  Responder Procedures   S-BFD Control packets are IP routed back to the initiator and will   have an IP header, UDP header, and BFD control header.  If an   SBFDReflector receives an S-BFD Control packet with a UDP source port   of 7784, the packet MUST be discarded.  Necessary values in the BFD   control header are described in [RFC7880].Section 6.1 describes   necessary values in the IP header and UDP header when an   SBFDReflector on the responder is sending S-BFD Control packets.6.1.  Details of S-BFD Control Packets Sent by SBFDReflector   o  The Destination IP Address field of the IP header MUST be copied      from the Source IP Address field of the received S-BFD Control      packet.   o  The Source IP Address field of the IP header MUST be set to a      local IP address that the initiator expects to be visible (i.e.,      not an IPv6 link-local address when the initiator is multiple hops      away).  The source IP address SHOULD be copied from the      Destination IP Address field of the received S-BFD Control packet,      except when it is from the 127/8 range for IPv4 or from the      0:0:0:0:0:ffff:7f00:0/104 range for IPv6.   o  The TTL / Hop Limit field of the IP header MUST be set to 255.   o  The UDP destination port MUST be copied from the received UDP      source port.   o  The UDP source port MUST be copied from the received UDP      destination port.Pignataro, et al.            Standards Track                    [Page 5]

RFC 7881          Seamless BFD for IPv4, IPv6, and MPLS        July 20167.  Security Considerations   Security considerations for S-BFD are discussed in [RFC7880].   Additionally, implementing the following measures will strengthen   security aspects of the mechanism described by this document:   o  Implementations MUST provide filtering capability based on source      IP addresses of received S-BFD Control packets; see [RFC2827].   o  Implementations MUST NOT act on received S-BFD Control packets      containing source Martian IP addresses (i.e., addresses that, by      application of the current forwarding tables, would not have their      return traffic routed back to the sender).   o  Implementations MUST ensure that response S-BFD Control packets      generated by the SBFDReflector and sent to the initiator have a      reachable target (e.g., destination IP address).8.  IANA Considerations   A new port number value, 7784, was allocated from the "Service Name   and Transport Protocol Port Number Registry".  The allocated registry   entry is:     Service Name (REQUIRED)       s-bfd     Transport Protocol(s) (REQUIRED)       udp     Assignee (REQUIRED)       IESG <iesg@ietf.org>     Contact (REQUIRED)       IETF Chair <chair@ietf.org>     Description (REQUIRED)       Seamless Bidirectional Forwarding Detection (S-BFD)     Reference (REQUIRED)RFC 7881     Port Number (OPTIONAL)       7784Pignataro, et al.            Standards Track                    [Page 6]

RFC 7881          Seamless BFD for IPv4, IPv6, and MPLS        July 20169.  References9.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <http://www.rfc-editor.org/info/rfc2119>.   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection              (BFD)",RFC 5880, DOI 10.17487/RFC5880, June 2010,              <http://www.rfc-editor.org/info/rfc5880>.   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection              (BFD) for IPv4 and IPv6 (Single Hop)",RFC 5881,              DOI 10.17487/RFC5881, June 2010,              <http://www.rfc-editor.org/info/rfc5881>.   [RFC7880]  Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.              Pallagatti, "Seamless Bidirectional Forwarding Detection              (S-BFD)",RFC 7880, DOI 10.17487/RFC7880, July 2016,              <http://www.rfc-editor.org/info/rfc7880>.9.2.  Informative References   [RFC791]   Postel, J., "Internet Protocol", STD 5,RFC 791,              DOI 10.17487/RFC791, September 1981,              <http://www.rfc-editor.org/info/rfc791>.   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6              (IPv6) Specification",RFC 2460, DOI 10.17487/RFC2460,              December 1998, <http://www.rfc-editor.org/info/rfc2460>.   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:              Defeating Denial of Service Attacks which employ IP Source              Address Spoofing",BCP 38,RFC 2827, DOI 10.17487/RFC2827,              May 2000, <http://www.rfc-editor.org/info/rfc2827>.   [RFC5884]  Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,              "Bidirectional Forwarding Detection (BFD) for MPLS Label              Switched Paths (LSPs)",RFC 5884, DOI 10.17487/RFC5884,              June 2010, <http://www.rfc-editor.org/info/rfc5884>.Pignataro, et al.            Standards Track                    [Page 7]

RFC 7881          Seamless BFD for IPv4, IPv6, and MPLS        July 2016Acknowledgements   The authors would like to thank the BFD WG members for helping to   shape the contents of this document.  In particular, significant   contributions were made by the following people: Marc Binderberger,   Jeffrey Haas, Santosh Pallagatti, Greg Mirsky, Sam Aldrin, Vengada   Prasad Govindan, Mallik Mudigonda, and Srihari Raghavan.Contributors   The following are key contributors to this document:      Tarek Saad, Cisco Systems, Inc.      Siva Sivabalan, Cisco Systems, Inc.      Nagendra Kumar, Cisco Systems, Inc.Authors' Addresses   Carlos Pignataro   Cisco Systems, Inc.   Email: cpignata@cisco.com   Dave Ward   Cisco Systems, Inc.   Email: wardd@cisco.com   Nobo Akiya   Big Switch Networks   Email: nobo.akiya.dev@gmail.comPignataro, et al.            Standards Track                    [Page 8]