Network Working Group                                   L. Dunbar
Internet Draft                                          Futurewei
Intended status: Standard                             K. Majumdar
Expires: February 4, 2023                              Microsoft
                                                          H. Wang
                                                           Huawei
                                                        G. Mishra
                                                          Verizon
                                                   August 4, 2022

           BGP AppMetaData for 5G Edge Computing Service
         draft-dunbar-idr-5g-edge-compute-app-meta-data-10

Abstract
   This draft describes the AppMetaData encoding in the BGP Path
   Attribute for egress routers to advertise the running status
   and environment of the directly attached 5G Edge Computing
   (EC) instances. The AppMetaData can be used by the ingress
   routers in the 5G Local Data Network to make path selection
   not only based on the routing distance but also the running
   environment of the destinations. The goal is to improve
   latency and performance for 5G EC services.

   The extension enables an EC server at one specific location to
   be more preferred than the others with the same IP address to
   receive data flows from a specific source (UE).

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79. This document may not be
   modified, and derivative works of it may not be created,
   except to publish it as an RFC and to translate it into
   languages other than English.

   Internet-Drafts are working documents of the Internet
   Engineering Task Force (IETF), its areas, and its working
   groups.  Note that other groups may also distribute working
   documents as Internet-Drafts.






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   Internet-Drafts are draft documents valid for a maximum of six
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   the document authors. All rights reserved.

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Table of Contents

   1. Introduction.............................................. 3
   2. Conventions used in this document......................... 3
   3. BGP Protocol Extension to advertise Load & Capacity....... 4
      3.1. Ingress Node BGP Path Selection Behavior............. 5
         3.1.1. AppMetaData Influenced BGP Path Selection....... 5
         3.1.2. Ingress Router Forwarding Behavior.............. 5
         3.1.3. Forwarding Behavior when UEs moving to new 5G
         Sites.................................................. 6
   4. Load Measurement and Site Preference AppMetaData.......... 7
      4.1. Load Measurement sub-TLV format...................... 7
      4.2. The Site Preference Index sub-TLV format............. 9
   5. Capacity Index AppMetaData............................... 10


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      5.1. Service Instance Attached Capacity Site Index....... 11
      5.2. BGP UPDATE with standalone Capacity Site Index...... 11
   6. AppMetaData Propagation Scope............................ 12
   7. Minimum Interval for Metrics Change Advertisement........ 13
   8. Manageability Considerations............................. 13
   9. Security Considerations.................................. 13
   10. IANA Considerations..................................... 13
   11. References.............................................. 14
      11.1. Normative References............................... 14
      11.2. Informative References............................. 14
   12. Acknowledgments......................................... 15

1. Introduction

   [5g-edge-Compute] describes the 5G Edge Computing background
   and how BGP can be used to advertise the running status and
   environment of the directly attached 5G edge computing (EC)
   servers. This document describes a new subTLV, AppMetaData,
   for egress routers to advertise the running status and
   environment for the directly attached Edge Computing (EC)
   servers. The AppMetaData can be used by the ingress routers in
   the 5G Local Data Network to make path selection not only
   based on the routing distance but also the running environment
   of the destinations. The goal is to improve latency and
   performance for 5G Edge Computing services.

2. Conventions used in this document

   A-ER:       Egress Router to an Application Server, [A-ER] is
               used to describe the last router that the
               Application Server is attached. For a 5G EC
               environment, the A-ER can be the gateway router to
               a (mini) Edge Computing Data Center.

   Application Server: An application server is a physical or
               virtual server that hosts the software system for
               the application.

   Application Server Location: Represent a cluster of servers at
               one location serving the same Application. One
               application may have a Layer 7 Load balancer,
               whose address(es) are reachable from an external
               IP network, in front of a set of application
               servers. From an IP network perspective, this


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               whole group of servers is considered as the
               Application server at the location.

   Edge Application Server: used interchangeably with Application
               Server throughout this document.

   EC:         Edge Computing

   Edge Hosting Environment: An environment providing the support
               required for Edge Application Server's execution.

               NOTE: The above terminologies are the same as
               those used in 3GPP TR 23.758

   Edge DC:    Edge Data Center, which provides the Edge
               Computing Hosting Environment. An Edge DC might
               host 5G core functions in addition to the
               frequently used application servers.

   gNB         next generation Node B

   L-DN:       Local Data Network

   PSA:        PDU Session Anchor (UPF)

   SSC:        Session and Service Continuity

   UE:         User Equipment

   UPF:        User Plane Function


   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. BGP Protocol Extension to advertise Load & Capacity

    The goal of the BGP extension is for egress routers to
    propagate the metrics about their running environment to


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    ingress routers. Here are some examples of the metrics
    propagated by the egress routers:
    - the Load Measurement Index for the attached EC Servers,

    - the Capacity Index, and

    - Site Preference Index.

    This section specifies the Load Index Sub-TLV, Capacity Sub-
    TLV, and the Site Preference Sub-TLV that can be carried by
    the Tunnel Encap Path Attribute [RFC9012] associated with the
    routes.

 3.1. Ingress Node BGP Path Selection Behavior

 3.1.1. AppMetaData Influenced BGP Path Selection

   When an ingress router receives BGP updates for the same IP
   address from multiple egress routers, all those egress routers
   are considered as the next hops for the IP address. For the
   selected EC services, the ingress router's BGP engine would
   call a Plugin function that can select paths based on the
   AppMetaData received. The Plugin function is called Load
   Compute Engine throughout this document.

   Suppose a destination address for 5G (S1:aa08::4450) can be
   reached by three next hops (R1, R2, R3). Further, suppose the
   local BGP's Compute Engine Identifies the R1 as the optimal
   next hop for flows to be sent to this destination
   (S1:aa08::4450). The Load Compute Engine can insert a higher
   weight for the tunnel associated with R1 for the prefix via
   the tunnel.

 3.1.2. Ingress Router Forwarding Behavior

   When the ingress router receives a packet and lookup the route
   in the FIB, it gets the destination prefix's whole path. It
   encapsulates the packet destined towards the optimal egress
   node.

   For subsequent packets belonging to the same flow, the ingress
   router needs to forward them to the same egress router unless
   the selected egress router is no longer reachable. Keeping
   packets from one flow to the same egress router, a.k.a. Flow
   Affinity, is supported by many commercial routers. Most
   registered EC services have relatively short flows.


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   How Flow Affinity is implemented is out of the scope for this
   document. Here is one example to illustrate how Flow Affinity
   can be achieved. This illustration is not to be standardized.

     For the registered EC services, the ingress node keeps a
     table of
     -   Service ID (i.e., IP address)
     -   Flow-ID
     -   Sticky Egress ID (egress router loopback address)
     -   A timer

     The Flow-ID in this table is to identify a flow, initialized
     to NULL. How Flow-ID is constructed is out of the scope for
     this document. Here is one example of constructing the Flow-
     ID:
       - For IPv6, the Flow-ID can be the Flow-ID extracted from
          the IPv6 packet header with or without the source
          address.
       - For IPv4, the Flow-ID can be the combination of the
          Source Address with or without the TCP/UDP Port number.

     The Sticky Egress ID is the egress node address for the same
     flow. [5G-Sticky-Service] describes several methods to
     derive the Sticky Egress ID.

     The Timer is always refreshed when a packet with the
     matching EC Service ID (IP address) is received by the node.

     If there is no Stick Egress ID present in the table for the
     EC Service ID, the forwarding plane can select a NextHop
     influenced by the Load Compute Engine. The forwarding plane
     encapsulates the packet with a tunnel to the chosen NextHop.
     The chosen NextHop and the Flow ID are recorded in the EC
     Service table entry.

   When the selected optimal NextHop (egress router) is no longer
   reachable, refer to Section 6 Soft Anchoring on how another
   path is selected.

 3.1.3. Forwarding Behavior when UEs moving to new 5G Sites

   When a UE moves to a new 5G eNB which is anchored to the same
   UPF, the packets from the UE traverse to the same ingress
   router. Path selection and forwarding behavior are same as
   before.




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   If the UE maintains the same IP address when anchored to a new
   UPF, the directly connected ingress router might use the
   information passed from a neighboring router to derive the
   optimal Next Hop for this route. [5G-Edge-Sticky] describes
   some methods for the ingress router connected to the UPF in
   the new site to consider the information passed from other
   ingress routers in selecting the optimal paths. The detailed
   algorithm is out of the scope of this document.

4. Load Measurement and Site Preference AppMetaData

   The Load Measurement and Site Preference AppMetaData attribute
   is encoded in an optional subTLV within the Tunnel Encap
   [RFC9012] Path Attribute.

   All values in the Sub-TLVs are unsigned 32 bits integers.

4.1. Load Measurement sub-TLV format

   Two types of Load Measurement Sub-TLVs are specified. One is
   to carry the aggregated cost Index based on a weighted
   combination of the collected measurements; another one is to
   carry the raw measurements of packets/bytes to/from the App
   Server address. The raw measurement is useful when ingress
   routers have embedded analytics relying on the raw
   measurements.

     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 (TBD1)           |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Measurement Period                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Aggregated Load Index to reach the App Server       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 2: Aggregated Load Index Sub-TLV














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   Raw Load Measurement sub-TLV has the following format:

     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 (TBD2)         |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Measurement Period                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           total number of packets to the AppServer            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           total number of packets from the AppServer          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           total number of bytes to the AppServer              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           total number of bytes from the AppServer            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  Figure 3: Raw Load Measurement Sub-TLV


     Type =TBD1: Aggregated Load Measurement Index derived from
     the Weighted combination of bytes/packets sent to/received
     from the App server:

     Index=w1*ToPackets+w2*FromPackes+w3*ToBytes+w4*FromBytes

     Where wi is a value between 0 and 1; w1+ w2+ w3+ w4 = 1.


     Type= TBD2: Raw measurements of packets/bytes to/from the
     App Server address.

     Measure Period: BGP Update period or user-specified period.



















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  4.2. The Site Preference Index sub-TLV format

   The site Preference Index is used to achieve Soft Anchoring
   [Section 5] an application flow from a UE to a specific
   location when the UE moves from one 5G site to another.

   The Preference Index sub-TLV has the following format:

      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 (TBD4)         |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Preference Index                            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 5: Preference Index Sub-TLV



   Note: "Site Preference Index" can be more stable for each
   site. If those values are configured to nodes, they might not
   need to be included in every BGP UPDATE.



























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5. Capacity Index AppMetaData

   Capacity Index indicates the capacity value for the site or
   pod where the EC service instances are instantiated. One Edge
   Cloud site (or Pod) can have larger capacity than another one.
   One Edge Site can be in full capacity, or reduced capacity.
   When there is a failure occurring at an Edge site (or pod),
   many instances can be impacted. Instead of many BGP UPDATE
   messages for each instance to the impacted ingress routers,
   the egress router can send one single BGP UPDATE indicating
   the capacity of the site. The ingress routers can switch all
   or a portion of the instances that are associated with the
   site depending on how much the site is degraded.

   Cloud Site/Pod failures and degradation include, but not
   limited to, a site capacity degradation or entire site going
   down caused by a variety of reasons, such as fiber cut
   connecting to the site or among pods within one site, cooling
   failures, insufficient backup power, cyber threats attacks,
   too many changes outside of the maintenance window, etc.
   Fiber-cut is not uncommon within a Cloud site or between
   sites.

   When those failure events happen, the Edge Cloud (egress)
   router visible to the ingress routers can be running fine.
   Therefore, the ingress routers can't use BFD to detect the
   failures.

   When a site capacity degrades or goes dark, there can be many
   routes impacted. In addition, the routes (i.e., the IP
   addresses) in an Edge Cloud Site might not be aggregated
   nicely, triggering very large number of BGP UPDATE messages
   (see RFC4271) when a failure occurs.

   The Capacity Index can be carried by an opaque Extended
   Community with a new subtype (Site Capacity Cost), by Tunnel-
   Encap subTLV, or wide community:

   The Opaque Extended community has (with High value = 0x03).

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 0x03 (1 octet)| Capacity-index|   Reserved    | Usage-Index   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Side-reference (2 octets)     |   Site Capacity Index         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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  - Sub Type: Capacity-Index subtype (TBD by IANA)

  - Usage-Index: Indicating if the Site Capacity Index is absolute
     value, relative to all the sites/pods attached to the BGP
     speaker, or percentage, etc.

  - Site Reference: The Site-reference can represent a group of
     routes within one site/pod, or locally significant Site/Pod
     identifer to represent capacity for all the routes (instances)
     in the site/pod. There could be many sites/pods connected to
     the egress router (a.k.a. Edge DC GW)

  - Site Capacity Index: representing the percentage of the site
     availability. When a site goes dark, the Index is set to 0.
     50 means 50% capacity functioning.


  5.1. Service Instance Attached Capacity Site Index

  The purpose of the Capacity Site index is to advertise the
  service instance's site reference identifier and the capacity
  value of the site.

  However, it is not necessary to include the Capacity Site
  Extended Community for every BGP Update message if there is no
  change to the site-reference identifier or value for the
  service instances.

  The ingress routers attach the Site-reference Identifier to
  the routes in the Routing table.

  5.2. BGP UPDATE with standalone Capacity Site Index

  When there are failures or degradation to a site, the
  corresponding egress router can send a BGP UPDATE with the
  Capacity Site Index Extended Community without attaching any
  routes.

  When an ingress router receives a BGP Update message from
  Router-X with the Site-Capacity Extended Community (Received-
  Site-Reference=t) but without specific routes attached, the
  ingress router performs the following steps:




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     For (i=0; i<RoutingTableSize; i++)
     {
        If (RoutingTable[i].NextHop == Router-X)
        {
           If (RoutingTable[i].Site-Reference == Received-Site-
           Reference-ID)
           {
              RoutingTable[i].Site-capacity = newly-received-
              site-capacity;
           }
        }

     }

  The new Site-Capacity value is applied to all routes that are
  associated with the Site-Reference ID with the NextHop being
  the Router-X.

  When a CPE receives BGP updates for the same IP address from
  multiple routers, all those egress routers are considered as
  the potential paths (or next hops) for the IP address (i.e.,
  if the BGP Add Path is supported). For the selected services,
  the ingress router's BGP engine would call a Plugin function
  that can select paths based on the cost associated with the
  client route received, such as Site-Capacity-Index, load index
  site preference, and network cost. The Plugin function is
  called Cost Compute Engine throughout this document.

  Suppose a destination address for S1:aa08::4450 can be reached
  by three next hops (R1, R2, R3). Further, suppose the local
  BGP's Compute Engine Identifies the R1 as the optimal next hop
  for flows to be sent to this destination (S1:aa08::4450). The
  Cost Compute Engine can insert a higher weight for the tunnel
  associated with R1 for the prefix via the tunnel.



6. AppMetaData Propagation Scope

   AppMetaData is only to be distributed to the relevant ingress
   nodes of the 5G EC local data networks. Only the ingress
   routers that are configured with the 5G EC services need to
   receive the AppMetaData for specific Service IDs.





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   For each registered EC service, a corresponding filter group
   can be formed on RR to represent the interested ingress
   routers that are interested in receiving the corresponding
   AppMetaData information.

7. Minimum Interval for Metrics Change Advertisement

   As the metrics change can impact the path selection, the
   Minimum Interval for Metrics Change Advertisement is
   configured to control the update frequency to avoid route
   oscillations. Default is 30s.

   Significant load changes at EC data centers can be triggered
   by short-term gatherings of UEs, like conventions, lasting a
   few hours or days, which are too short to justify adjusting EC
   server capacities among DCs. Therefore, the load metrics
   change rate can be in the magnitude of hours or days.

8. Manageability Considerations

     To be added.

9. Security Considerations


   To be added.

10. IANA Considerations

   Need IANA to assign three new Sub-TLV types under the Tunnel
   Encap attribute [RFC9012] :

     Type = TBD1: Aggregated Load Measurement Index derived from
     the Weighted combination of bytes/packets sent to/received
     from the App server.

     Type = TBD2: Raw measurements of packets/bytes to/from the
     App Server address.

     Type = TBD3: Site preference value sub-TLV

   Need IANA to assign one new sub-TLV type under the Opaque
   Extended Community:

     Type = TBD4: Capacity value sub-TLV


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11. References


  11.1. Normative References

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

   [RFC4364] E. rosen, Y. Rekhter, "BGP/MPLS IP Virtual Private
             networks (VPNs)", Feb 2006.

   [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>.

   [RFC8200] s. Deering R. Hinden, "Internet Protocol, Version 6
             (IPv6) Specification", July 2017

   [RFC9012] E. Rosen, et al "BGP Tunnel Encapsulation
             Attribute", RFC9012, April 2021.


  11.2. Informative References

   [3GPP-EdgeComputing] 3GPP TR 23.748, "3rd Generation
             Partnership Project; Technical Specification Group
             Services and System Aspects; Study on enhancement of
             support for Edge Computing in 5G Core network
             (5GC)", Release 17 work in progress, Aug 2020.

   [5G-EC-Metrics] L. Dunbar, H. Song, J. Kaippallimalil, "IP
             Layer Metrics for 5G Edge Computing Service", draft-
             dunbar-ippm-5g-edge-compute-ip-layer-metrics-00,
             work-in-progress, Oct 2020.

   [5g-edge-Compute] L. Dunbar, K. Majumdar, H. Wang, and G.
             Mishra, "BGP Usage for 5G Edge Computing service
             Metadata", draft-dunbar-idr-5g-edge-compute-bgp-
             usage-00, work-in-progress, July 2022.



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   [5G-Edge-Sticky] L. Dunbar, J. Kaippallimalil, "IPv6 Solution
             for 5G Edge Computing Sticky Service", draft-dunbar-
             6man-5g-ec-sticky-service-00, work-in-progress, Oct
             2020.

   [RFC5521] P. Mohapatra, E. Rosen, "The BGP Encapsulation
             Subsequent Address Family Identifier (SAFI) and the
             BGP Tunnel Encapsulation Attribute", April 2009.

   [SDWAN-EDGE-Discovery] L. Dunbar, S. Hares, R. Raszuk, K.
             Majumdar, "BGP UPDATE for SDWAN Edge Discovery",
             draft-ietf-idr-sdwan-edge-discovery-03, July 2022.



12. Acknowledgments

   Acknowledgements to Robert Raszuk, Sue Hares, Donald Eastlake
   for their review and contributions.

   This document was prepared using 2-Word-v2.0.template.dot.



Authors' Addresses

   Linda Dunbar
   Futurewei
   Email: ldunbar@futurewei.com

   Kausik Majumdar
   Microsoft
   Email: kmajumdar@microsoft.com

   Haibo Wang
   Huawei
   Email: rainsword.wang@huawei.com

   Gyan Mishra
   Verizon
   Email: gyan.s.mishra@verizon.com



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