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Internet Engineering Task Force (IETF)                          K. PatelRequest for Comments: 8395                                        ArrcusUpdates:4761                                                 S. BoutrosCategory: Standards Track                                         VMwareISSN: 2070-1721                                                 J. Liste                                                                   Cisco                                                                  B. Wen                                                                 Comcast                                                              J. Rabadan                                                                   Nokia                                                               June 2018Extensions to BGP-Signaled Pseudowires toSupport Flow-Aware Transport LabelsAbstract   This document defines protocol extensions required to synchronize   flow label states among Provider Edges (PEs) when using the BGP-based   signaling procedures.  These protocol extensions are equally   applicable to point-to-point Layer 2 Virtual Private Networks   (L2VPNs).  This document updatesRFC 4761 by defining new flags in   the Control Flags field of the Layer2 Info Extended Community.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 athttps://www.rfc-editor.org/info/rfc8395.Patel, et al.                Standards Track                    [Page 1]

RFC 8395               BGP-Signaled FAT PW Labels              June 2018Copyright Notice   Copyright (c) 2018 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   (https://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.Table of Contents1. Introduction ....................................................21.1. Requirements Language ......................................32. Modifications to the Layer2 Info Extended Community .............43. Signaling the Presence of the Flow Label ........................54. IANA Considerations .............................................65. Security Considerations .........................................66. References ......................................................76.1. Normative References .......................................76.2. Informative References .....................................7   Acknowledgements ...................................................8   Contributors .......................................................8   Authors' Addresses .................................................91.  Introduction   The mechanism described in [RFC6391] uses an additional label (Flow   Label) in the MPLS label stack to allow Label Switching Routers   (LSRs) to balance flows within Pseudowires (PWs) at a finer   granularity than the individual PWs across the Equal Cost Multiple   Paths (ECMPs) that exists within the Packet Switched Network (PSN).   Furthermore, [RFC6391] defines the LDP protocol extensions required   to synchronize the flow label states between the ingress and egress   PEs when using the signaling procedures defined in the [RFC8077].   A PW [RFC3985] is transported over one single network path, even if   ECMPs exist between the ingress and egress PW provider edge (PE)   equipment.  This is required to preserve the characteristics of the   emulated service.Patel, et al.                Standards Track                    [Page 2]

RFC 8395               BGP-Signaled FAT PW Labels              June 2018   This document introduces an optional mode of operation allowing a PW   to be transported over ECMPs, for example when the use of ECMPs is   known to be beneficial to the operation of the PW.  This   specification uses the principles defined in [RFC6391] and augments   the BGP-signaling procedures of [RFC4761] and [RFC6624].  The use of   a single path to preserve the packet delivery order remains the   default mode of operation of a PW and is described in [RFC4385] and   [RFC4928].   High-bandwidth Ethernet-based services are a prime example that use   of the optional mode benefits from the ability to load-balance flows   in a PW over multiple PSN paths.  In general, load-balancing is   applicable when the PW attachment circuit bandwidth and PSN core link   bandwidth are of the same order of magnitude.   To achieve the load-balancing goal, [RFC6391] introduces the notion   of an additional Label Stack Entry (LSE) (flow label) located at the   bottom of the stack (right after PW LSE).  LSRs commonly generate a   hash of the label stack in order to discriminate and distribute flows   over available ECMPs.  The presence of the flow label (closely   associated to a flow determined by the ingress PE) will normally   provide the greatest entropy.   Furthermore, following the procedures for inter-AS scenarios   described inSection 3.4 of [RFC4761], the flow label should never be   handled by the ASBRs; only the terminating PEs on each AS will be   responsible for popping or pushing this label.  This is equally   applicable to Method B as described inSection 3.4.2 of [RFC4761],   where ASBRs are responsible for swapping the PW label as traffic   traverses from ASBR to PE and ASBR to ASBR.  Therefore, the flow   label will remain untouched across AS boundaries.1.1.  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 inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.Patel, et al.                Standards Track                    [Page 3]

RFC 8395               BGP-Signaled FAT PW Labels              June 20182.  Modifications to the Layer2 Info Extended Community   The Layer2 Info Extended Community is used to signal control   information about the PWs to be set up.  The Extended Community   format is described in [RFC4761].  The format of this Extended   Community is described as:            +------------------------------------+            | Extended Community type (2 octets) |            +------------------------------------+            |  Encaps Type (1 octet)             |            +------------------------------------+            |  Control Flags (1 octet)           |            +------------------------------------+            |  Layer-2 MTU (2 octets)            |            +------------------------------------+            |  Reserved (2 octets)               |            +------------------------------------+            Figure 1: Layer2 Info Extended Community   Control Flags:   This field contains bit flags relating to the control information   about PWs.  This field is augmented with a definition of two new   flags fields.             0 1 2 3 4 5 6 7            +-+-+-+-+-+-+-+-+            |Z|Z|Z|Z|T|R|C|S|      (Z = MUST Be Zero)            +-+-+-+-+-+-+-+-+            Figure 2: Control Flags Bit Vector   With reference to the Control Flags Bit Vector, the following bits in   the Control Flags are defined.  The remaining bits, designated "Z",   MUST be set to zero when sending and MUST be ignored when receiving   this Extended Community.      T   When the bit value is 1, the PE announces the ability to send          a PW packet that includes a flow label.  When the bit value is          0, the PE is indicating that it will not send a PW packet          containing a flow label.      R   When the bit value is 1, the PE is able to receive a PW packet          with a flow label present.  When the bit value is 0, the PE is          unable to receive a PW packet with the flow label present.Patel, et al.                Standards Track                    [Page 4]

RFC 8395               BGP-Signaled FAT PW Labels              June 2018      C   Defined in [RFC4761].      S   Defined in [RFC4761].3.  Signaling the Presence of the Flow Label   As part of the PW signaling procedures described in [RFC4761], a   Layer2 Info Extended Community is advertised in the Virtual Private   LAN Service (VPLS) BGP Network Layer Reachability Information (NLRI).   A PE that wishes to send a flow label in a PW packet MUST include in   its VPLS BGP NLRI a Layer2 Info Extended Community using Control   Flags field with T = 1.   A PE that is willing to receive a flow label in a PW packet MUST   include in its VPLS BGP NLRI a Layer2 Info Extended Community using   Control Flags field with R = 1.   A PE that receives a VPLS BGP NLRI containing a Layer2 Info Extended   Community with R = 0 MUST NOT include a flow label in the PW packet.   Therefore, a PE sending a Control Flags field with T = 1 and   receiving a Control Flags field with R = 1 MUST include a flow label   in the PW packet.  With any other combination, a PE MUST NOT include   a flow label in the PW packet.   A PE MAY support the configuration of the flow label (T and R bits)   on a per-service basis (e.g., a VPLS VPN Forwarding Instance (VFI)).   Furthermore, it is also possible that on a given service, PEs may not   share the same flow label settings.  The presence of a flow label is   therefore determined on a per-peer basis and according to the local   and remote T and R bit values.  For example, a PE part of a VPLS and   with a local T = 1 must only transmit traffic with a flow label to   those peers that signaled R = 1.  If the same PE has local R = 1, it   must only expect to receive traffic with a flow label from peers with   T = 1.  Any other traffic must not have a flow label.  A PE expecting   to receive traffic from a remote peer with a flow label MAY drop   traffic that has no flow label.  A PE expecting to receive traffic   from a remote peer with no flow label MAY drop traffic that has a   flow label.   Modification of flow label settings may impact traffic over a PW, as   these could trigger changes in the PEs data-plane programming (i.e.,   imposition/disposition of the flow label).  This is an   implementation-specific behavior and is outside the scope of this   document.Patel, et al.                Standards Track                    [Page 5]

RFC 8395               BGP-Signaled FAT PW Labels              June 2018   The signaling procedures in [RFC4761] state that the unspecified bits   in the Control Flags field (bits 0-5) MUST be set to zero when   sending and MUST be ignored when receiving.  The signaling procedure   described here is therefore backwards compatible with existing   implementations.  A PE not supporting the extensions described in   this document will always advertise a value of zero in the R bit;   therefore, a flow label will never be included in a packet sent to it   by one of its peers.  Similarly, it will always advertise a value of   zero in the T bit; therefore, a peer will know that a flow label will   never be included in a packet sent by it.   Note that what is signaled is the desire to include the flow LSE in   the label stack.  The value of the flow label is a local matter for   the ingress PE, and the label value itself is not signaled.4.  IANA Considerations   Although [RFC4761] defined a Control Flags Bit Vector as part of the   Layer2 Info Extended Community, it did not ask for the creation of a   registry.   Per this document, IANA has created the "Layer2 Info Extended   Community Control Flags Bit Vector" registry   <https://www.iana.org/assignments/bgp-extended-communities>.   Based on [RFC4761] and this document, the initial contents of this   registry are as follows:   Value   Name                               Reference   -----   --------------------------------   --------------   T       Request to send a flow label       This document   R       Ability to receive a flow label    This document   C       Presence of a Control WordRFC 4761   S       Sequenced delivery of framesRFC 4761   As per [RFC4761] and this document, the remaining bits are   unassigned, and MUST be set to zero when sending and MUST be ignored   when receiving the Layer2 Info Extended Community.5.  Security Considerations   This extension to BGP does not change the underlying security issues   inherent in [RFC4271] and [RFC4761].Patel, et al.                Standards Track                    [Page 6]

RFC 8395               BGP-Signaled FAT PW Labels              June 20186.  References6.1.  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,              <https://www.rfc-editor.org/info/rfc2119>.   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed.,              "A Border Gateway Protocol 4 (BGP-4)",RFC 4271,              DOI 10.17487/RFC4271, January 2006,              <https://www.rfc-editor.org/info/rfc4271>.   [RFC4761]  Kompella, K., Ed., and Y. Rekhter, Ed., "Virtual Private              LAN Service (VPLS) Using BGP for Auto-Discovery and              Signaling",RFC 4761, DOI 10.17487/RFC4761, January 2007,              <https://www.rfc-editor.org/info/rfc4761>.   [RFC6391]  Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V.,              Regan, J., and S. Amante, "Flow-Aware Transport of              Pseudowires over an MPLS Packet Switched Network",RFC 6391, DOI 10.17487/RFC6391, November 2011,              <https://www.rfc-editor.org/info/rfc6391>.   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC 2119 Key Words",BCP 14,RFC 8174,              DOI 10.17487/RFC8174, May 2017,              <https://www.rfc-editor.org/info/rfc8174>.6.2.  Informative References   [RFC3985]  Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation              Edge-to-Edge (PWE3) Architecture",RFC 3985,              DOI 10.17487/RFC3985, March 2005,              <https://www.rfc-editor.org/info/rfc3985>.   [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for              Use over an MPLS PSN",RFC 4385, DOI 10.17487/RFC4385,              February 2006, <https://www.rfc-editor.org/info/rfc4385>.   [RFC8077]  Martini, L., Ed., and G. Heron, Ed., "Pseudowire Setup and              Maintenance Using the Label Distribution Protocol (LDP)",              STD 84,RFC 8077, DOI 10.17487/RFC8077, February 2017,              <https://www.rfc-editor.org/info/rfc8077>.Patel, et al.                Standards Track                    [Page 7]

RFC 8395               BGP-Signaled FAT PW Labels              June 2018   [RFC4928]  Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal              Cost Multipath Treatment in MPLS Networks",BCP 128,RFC 4928, DOI 10.17487/RFC4928, June 2007,              <https://www.rfc-editor.org/info/rfc4928>.   [RFC6624]  Kompella, K., Kothari, B., and R. Cherukuri, "Layer 2              Virtual Private Networks Using BGP for Auto-Discovery and              Signaling",RFC 6624, DOI 10.17487/RFC6624, May 2012,              <https://www.rfc-editor.org/info/rfc6624>.Acknowledgements   The authors would like to thank Bertrand Duvivier and John Drake for   their review and comments.Contributors   In addition to the authors listed above, the following individuals   also contributed to this document:      Eric Lent      John Brzozowski      Steven CotterPatel, et al.                Standards Track                    [Page 8]

RFC 8395               BGP-Signaled FAT PW Labels              June 2018Authors' Addresses   Keyur Patel   Arrcus   Email: keyur@arrcus.com   Sami Boutros   VMware   Email: boutros.sami@gmail.com   Jose Liste   Cisco   Email: jliste@cisco.com   Bin Wen   Comcast   Email: bin_wen@cable.comcast.com   Jorge Rabadan   Nokia   Email: jorge.rabadan@nokia.comPatel, et al.                Standards Track                    [Page 9]