\
dmm                                                             Z. Zhang
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                                K. Patel
Expires: 8 September 2022                                         Arrcus
                                                           S. Matsushima
                                                                Softbank
                                                            7 March 2022


                  BGP Signaling for Mobile User Plane
                   draft-zpm-dmm-mup-bgp-signaling-00

Abstract

   This document specifies BGP signaling for router-based 5G User Plane
   using Mobile User Plane SAFI and some of its route types as specified
   in [draft-mpmz-idr-mup-safi].

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
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   This Internet-Draft will expire on 8 September 2022.

Copyright Notice

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

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   provided without warranty as described in the Revised BSD License.



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Table of Contents

   1.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminologies . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Analysis of SRv6 specific aspects of
           [I-D.mpmz-dmm-mup-safi] . . . . . . . . . . . . . . . . .   3
     2.1.  BGP Discovery Direct Route  . . . . . . . . . . . . . . .   3
     2.2.  BGP Discovery Interwork Route . . . . . . . . . . . . . .   3
   3.  Optional Type 3 Session Transform (ST3) Route . . . . . . . .   4
   4.  Specifications  . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  BGP Encodings . . . . . . . . . . . . . . . . . . . . . .   5
       4.1.1.  GTP PW Label Extended Community . . . . . . . . . . .   5
       4.1.2.  Type 3 Session Transform (ST3) route  . . . . . . . .   5
     4.2.  Procedures  . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Background

   5G [_3GPP-23.501] User Plane uses N4 signaling between Session
   Management Function (SMF) and User Plane Function (UPF), and N2
   signaling between Access & Mobility Management Function (AMF) and
   Access Nodes (AN).  A traditional UPF device is typically centrally
   deployed and uses GTP tunnels between itself and ANs for data traffic
   to/from User Equipment (UEs).  The GTP tunnels are set up by the N4
   and N2 signaling, and the forwarding model on a UPF is quite
   different from that on a typical router.

   UPFs can also be deployed in distributed fashion and still provide
   persistent IP address for UEs if needed, as described in
   [I-D.zzhang-dmm-5g-distributed-upf].

   Some operators may desire to deploy UPFs that are implemented more
   like a router with BGP instead of N4 signaling.  GTP tunneling can
   still be used or it can be partially replaced by SRv6/MPLS tunneling.
   It does not require any change to the 3GPP architecture, signaling
   and deployment model, but a controller is used to convert N4
   signaling to BGP, as described in [I-D.mhkk-dmm-srv6mup-architecture]
   and [I-D.mpmz-dmm-mup-safi].

   The above two drafts are both SRv6 specific.  However, BGP signaling
   from the controller based on N4 signaling can be done without being
   SRv6 or even SR specific at all.  This document specifies
   corresponding BGP signaling and procedures for both central and



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   distributed deployment models with integration with wireline VPN
   services as described in [I-D.zzhang-dmm-5g-distributed-upf],
   [I-D.mhkk-dmm-srv6mup-architecture], and [I-D.mpmz-dmm-mup-safi].

1.1.  Terminologies

   Terminologies of 5G, or those used in [I-D.mpmz-dmm-mup-safi] and
   [I-D.mhkk-dmm-srv6mup-architecture] are omitted here for now.  It is
   expected that audience of this document are familiar with them or can
   refer to the relevant documents.

2.  Analysis of SRv6 specific aspects of [I-D.mpmz-dmm-mup-safi]

   The goal of this document is to specify encoding and procedures that
   work for both MPLS, SR-MPLS as well as SRv6.  Therefore, we first
   look at the SRv6 specific aspects of [I-D.mpmz-dmm-mup-safi].

2.1.  BGP Discovery Direct Route

   Per [I-D.mpmz-dmm-mup-safi]:

  "The Discovery Direct route is generated by the MUP PE when a routing
  instance accommodates a Direct type MUP Segment, e.g., N6 interface or
  routes on DN side in 3GPP 5G specific case.  It generates the
  Discovery Direct Route per each routing instance for the MUP Segment."

   When a MUP GW receives a BGP Type 2 Session Transform (ST2) Route,
   which advertises the association of PDU Session TEID (on the UPF
   side) and a DN VPN, a corresponding Direct Route is matched to set up
   forwarding state on the GW so that it can decapsulate incoming GTP
   packets from gNB/AN and then send to the advertising MUP PE of the
   Direct Route using the Prefix SID in the Direct Route.  The Prefix
   SID has an End.DT2/4/6 or End.DX2/4/6 behavior.

   In the non-SR case (and SR-MPLS or SRv6 as well), this route can be
   replaced by the "VPN-IP default route" in [RFC7024].  The VRF table
   label in the route is used to send traffic by the GW to the MUP PE
   after GTP decapsulation.

2.2.  BGP Discovery Interwork Route

   Per [I-D.mpmz-dmm-mup-safi]:









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   "The Discovery Interwork route is generated by the MUP GW when a
   routing instance accommodates an Interwork type MUP Segment, e.g., N3
   interfaces or routes on RAN side in 3GPP 5G specific case.  It
   generates route per each N3RAN IP prefix and stores the route in the
   routing instance of N3RAN.  The IP prefix MAY include a gNodeB
   address which is connecting to the MUP GW."

   Basically, it is a route for a gNB/AN address in the N3RAN.  These
   routes are put into N3RAN RIB.  When a MUP PE receives a BGP Type 1
   Session Transform (ST1) route, the Endpoint Address in the ST1 NLRI
   is resolved in the N3RAN RIB, and the Prefix SRv6 SID associated with
   the Interwork Route, which has the End.GTP4/6.E behavior on the GW,
   is used send DownLink (DL) traffic from the MUP PE towards the gNB/AN
   via the GW.

   In the non-SR case (and SR-MPLS or SRv6 as well), this route can
   simply be replaced with a regular host route for the gNB/AN.  In case
   of MPLS or SR-MPLS, an "IP/UDP Payload PseudoWire"
   [I-D.zzhang-pals-pw-for-ip-udp-payload] label for GTP is encoded in
   an Extended Community so that the MUP PE can use it to send DL
   traffic with GTP encapsulation but w/o IP/UDP header to the GW, who
   will add the IP/UDP header and send the resulting GTP packet to the
   gNB/AN.

   The PW label is encoded in an EC because only the DL traffic should
   use the PW label and other traffic towards the gNB/AN should not.

   In case of SRv6, the same Prefix SID that would be attached to the
   Interwork Segment route can be attached to the regular gNB/AN host
   route that replaces the Interwork Segment route.

3.  Optional Type 3 Session Transform (ST3) Route

   In [I-D.mpmz-dmm-mup-safi], the ST1 route only has the TEID and
   endpoint address for the gNB/AN side for DL traffic.  For UpLink (UL)
   traffic, the ST2 route has the TEID prefix and endpoint address for
   the UPF side, so that the GW can determine which DN the traffic
   belongs to.

   It is quite possible that the TEID assigned by the SMF are per-
   session and do not fall into prefix ranges nicely.  Unless the MUP
   controller intelligently aggregate individual per-session ST2 routes,
   a MUP GW that also acts as a MUP PE will receive individual per-
   session ST1 and ST2 routes.  For that reason, an optional ST3 route
   is introduced to combine ST1 and ST2 routes.

4.  Specifications




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4.1.  BGP Encodings

   A Type 3 Session Transform (ST3) route, and a GTP PW Label Extended
   Community are specified in this section.

4.1.1.  GTP PW Label Extended Community

   The GTP PW Label Extended Community is a BGP MUP Extended Community
   of sub-type "GTP PW Label" (value to be assigned by IANA).

   The encoding is as following:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Type=MUP EC   | Sub-Type=TBD  |  Reserved=0                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Reserved=0   |          GTP PW Label                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.1.2.  Type 3 Session Transform (ST3) route

   A new Route Type for BGP-MUP NLRI is added:

          + 5 - Type 3 Session Transform (ST3) route;

   It is similar to the ST1 route:

        +-----------------------------------+
        |           RD  (8 octets)          |
        +-----------------------------------+
        |      Prefix Length (1 octet)      |
        +-----------------------------------+
        |         Prefix (variable)         |
        +-----------------------------------+
        | Architecture specific (variable)  |
        +-----------------------------------+

   For 3gpp-5g, the Architecture Specific part of the NLRI encodes the
   <UPF Address, UPF TEID, AN Address, AN TEID, QFI> parameters of the
   session that the route is for:











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        +-----------------------------------+
        |          QFI (1 octet)            |
        +-----------------------------------+
        |       AN TEID (4 octets)          |
        +-----------------------------------+
        |     AN Address Length (1 octet)   |
        +-----------------------------------+
        |     AN  Address (variable)        |
        +-----------------------------------+
        |      UPF TEID (4 octets)          |
        +-----------------------------------+
        |     UPF Address Length (1 octet)  |
        +-----------------------------------+
        |     UPF Address (variable)        |
        +-----------------------------------+

   The route is a combination of ST1 and ST2 routes, in that:

   *  The QFI, AN TEID, and AN Address information correspond to the
      fields in the 3gpp-5g ST1 Route Type specific BGP-MUP NLRI:

         +-----------------------------------+
         |          TEID (4 octets)          |
         +-----------------------------------+
         |          QFI (1 octet)            |
         +-----------------------------------+
         | Endpoint Address Length (1 octet) |
         +-----------------------------------+
         |    Endpoint Address (variable)    |
         +-----------------------------------+

   *  The UPF Address info corresponds to the Endpoint fields in ST2
      route:

         +-----------------------------------+
         |           RD  (8 octets)          |
         +-----------------------------------+
         |      Endpoint Length (1 octet)    | &lt;---
         +-----------------------------------+
         |      Endpoint Address (variable)  | &lt;---
         +-----------------------------------+
         | Architecture specific Endpoint    |
         |         Identifier (variable)     |
         +-----------------------------------+

   *  The UPF TEID field corresponds to the TEID in the 3gpp-5g ST2
      Route Type specific BGP-MUP NLRI:




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         +-----------------------------------+
         |          TEID (0-4 octets)        |
         +-----------------------------------+

4.2.  Procedures

   The procedures are inline with those in [I-D.mpmz-dmm-mup-safi] and
   [I-D.mhkk-dmm-srv6mup-architecture].

   Details will be added a future revision.

5.  Security Considerations

   To be provided.

6.  IANA Considerations

   Requests to be made for the BGP encodings in Section 4.1.  Details
   will be added in a future revision.

7.  References

7.1.  Normative References

   [I-D.ietf-dmm-srv6-mobile-uplane]
              Matsushima, S., Filsfils, C., Kohno, M., Garvia, P. C.,
              Voyer, D., and C. E. Perkins, "Segment Routing IPv6 for
              Mobile User Plane", Work in Progress, Internet-Draft,
              draft-ietf-dmm-srv6-mobile-uplane-18, 18 February 2022,
              <https://www.ietf.org/archive/id/draft-ietf-dmm-srv6-
              mobile-uplane-18.txt>.

   [I-D.mhkk-dmm-srv6mup-architecture]
              Matsushima, S., Horiba, K., Khan, A., Kawakami, Y.,
              Murakami, T., Patel, K., Kohno, M., Kamata, T., Garvia, P.
              C., Voyer, D., Zadok, S., Meilik, I., Agrawal, A.,
              Perumal, K., and J. Horn, "Segment Routing IPv6 Mobile
              User Plane Architecture for Distributed Mobility
              Management", Work in Progress, Internet-Draft, draft-mhkk-
              dmm-srv6mup-architecture-02, 7 March 2022,
              <https://www.ietf.org/archive/id/draft-mhkk-dmm-srv6mup-
              architecture-02.txt>.









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   [I-D.zzhang-pals-pw-for-ip-udp-payload]
              Zhang, Z. and K. Patel, "PW for IP/UDP Payload without IP/
              UDP Headers", Work in Progress, Internet-Draft, draft-
              zzhang-pals-pw-for-ip-udp-payload-01, 4 March 2022,
              <https://www.ietf.org/archive/id/draft-zzhang-pals-pw-for-
              ip-udp-payload-01.txt>.

   [RFC7024]  Jeng, H., Uttaro, J., Jalil, L., Decraene, B., Rekhter,
              Y., and R. Aggarwal, "Virtual Hub-and-Spoke in BGP/MPLS
              VPNs", RFC 7024, DOI 10.17487/RFC7024, October 2013,
              <https://www.rfc-editor.org/info/rfc7024>.

7.2.  Informative References

   [I-D.ietf-bess-srv6-services]
              Dawra, G., Filsfils, C., Talaulikar, K., Raszuk, R.,
              Decraene, B., Zhuang, S., and J. Rabadan, "SRv6 BGP based
              Overlay Services", Work in Progress, Internet-Draft,
              draft-ietf-bess-srv6-services-12, 5 March 2022,
              <https://www.ietf.org/archive/id/draft-ietf-bess-srv6-
              services-12.txt>.

   [I-D.zzhang-dmm-5g-distributed-upf]
              Zhang, Z., Patel, K., and T. Jiang, "5G Distributed UPFs",
              Work in Progress, Internet-Draft, draft-zzhang-dmm-5g-
              distributed-upf-00, 6 March 2022,
              <https://www.ietf.org/archive/id/draft-zzhang-dmm-5g-
              distributed-upf-00.txt>.

   [RFC4363]  Levi, D. and D. Harrington, "Definitions of Managed
              Objects for Bridges with Traffic Classes, Multicast
              Filtering, and Virtual LAN Extensions", RFC 4363,
              DOI 10.17487/RFC4363, January 2006,
              <https://www.rfc-editor.org/info/rfc4363>.

   [_3GPP-23.501]
              "System architecture for the 5G System (5GS), V17.3.0",
              December 2021.

Authors' Addresses

   Zhaohui Zhang
   Juniper Networks
   Email: zzhang@juniper.net


   Keyur Patel
   Arrcus



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   Email: keyur@arrcus.com


   Satoru Matsushima
   Softbank
   Email: satoru.matsushima@g.softbank.co.jp













































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