BGP AppMetaData for 5G Edge Service
draft-dunbar-idr-5g-edge-compute-app-meta-data-13

Network Working Group                                   L. Dunbar
Internet Draft                                          Futurewei
Intended status: Standard                             K. Majumdar
Expires: February 22, 2023                              Microsoft
                                                          H. Wang
                                                           Huawei
                                                        G. Mishra
                                                          Verizon
                                                  August 22, 2022

                BGP AppMetaData for 5G Edge Service
         draft-dunbar-idr-5g-edge-compute-app-meta-data-13

Abstract
   This draft describes three new sub-TLVs for egress routers to
   advertise the AppMetaData of the directly attached edge
   services (ES). 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 cost but also the running
   environment of the edge services. The goal is to improve
   latency and performance for 5G edge services.

   The extension enables an edge service at one specific location
   to be more preferred than the others with the same IP address
   (ANYCAST) to receive data flows from a specific source, like
   specific User Equipment (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.

xxx, et al.           Expires February 22, 2023          [Page 1]
Internet-Draft      AppMetaData for 5G EC Service

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed
   at http://www.ietf.org/shadow.html

   This Internet-Draft will expire on April 7, 2021.

Copyright Notice

   Copyright (c) 2022 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
   (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.

Table of Contents

   1. Introduction.............................................. 3
   2. Conventions used in this document......................... 4
   3. BGP Protocol Extension to advertise Load & Capacity....... 5
      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.............. 6
         3.1.3. Forwarding Behavior when UEs moving to new 5G
         Sites.................................................. 6
   4. AppMetaData Encoding...................................... 6
      4.1. The Site Preference Index sub-TLV format............. 7
      4.2. Capacity Index AppMetaData........................... 8
         4.2.1. Capacity Site Index attached to services........ 9

Dunbar, et al.        Expires February 22, 2023          [Page 2]
Internet-Draft      AppMetaData for 5G EC Service

         4.2.2. BGP UPDATE with standalone Capacity Site Index.. 9
      4.3. Load Measurement sub-TLV format..................... 10
   5. Consideration for Optimal Paths Selection................ 11
   6. AppMetaData Propagation Scope............................ 12
   7. Minimum Interval for Metrics Change Advertisement........ 12
   8. Manageability Considerations............................. 12
   9. Security Considerations.................................. 12
   10. IANA Considerations..................................... 13
   11. References.............................................. 13
      11.1. Normative References............................... 13
      11.2. Informative References............................. 14
   12. Appendix A.............................................. 14
      12.1. Example of Flow Affinity........................... 14
   13. 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 services. Besides
   the Radio Access, 5G is characterized by having edge services
   closer to the Cell Towers reachable by Local Data Networks
   (LDN) [3GPP TS 23.501]. From IP network perspective, the 5G
   LDN is a limited domain with edge services a few hops away
   from the ingress nodes. Only selective services by UEs are
   considered as 5G Edge Services.

   This document describes three new sub-TLVs for egress routers
   to advertise the AppMetaData of the directly attached edge
   services. The AppMetaData in this document refer to edge
   services' site capacity, the site preference, and the load
   index, that are further explained in Section 3. Note: the
   proposed AppMetaData are not intended for the services
   reachable via the networks outside the 5G LDN. 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 edge cloud
   sites. The goal is to improve latency and performance for 5G
   edge services.

   The extension is targeted for single domain iBGP.  AppMetaData
   is only attached to the services (routes) hosted in the 5G
   edge cloud sites, which are only a small subset of services
   initiated from UEs. E.g., not for UEs accessing many internet
   sites.

Dunbar, et al.        Expires February 22, 2023          [Page 3]
Internet-Draft      AppMetaData for 5G EC Service

2. Conventions used in this document

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

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

   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 Hosting
               Environment for the edge services. An Edge DC
               might host 5G core functions in addition to the
               frequently used application servers.

   gNB         next generation Node B

   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

Dunbar, et al.        Expires February 22, 2023          [Page 4]
Internet-Draft      AppMetaData for 5G EC Service

   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
    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 edge services, the ingress router's BGP engine would
   call a Plugin function that can select paths based on the
   AppMetaData received. [5G-EC-Metrics] has an example algorithm
   to compute the weighted path cost based on the AppMetaData
   carried by the sub-TLVs specified in this document. The Plugin
   function is called Cost Compute Engine throughout this
   document.

   Suppose a destination address for a service (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
   (aa08::4450). The Cost Compute Engine can insert a higher
   weight for the tunnel associated with R1 for the prefix via
   the tunnel. Suppose BGP Add Path is supported [RFC7911], all
   three paths can be added to the FIB who can choose the optimal
   paths for the received data packets.

Dunbar, et al.        Expires February 22, 2023          [Page 5]
Internet-Draft      AppMetaData for 5G EC Service

 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.

   How Flow Affinity is implemented is out of the scope for this
   document. Appendix A has one example illustrating achieving
   flow affinity.

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

   When a UE moves to a new 5G gNB 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.

   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. AppMetaData Encoding

   There are three types AppMetaData: Capacity Index Value, Site
   Preference Value, and Load Cost. They are encoded in an
   optional sub-TLV within the Tunnel Encap [RFC9012] Path
   Attribute.

   For routes associated with a specific tunnel, the AppMetaData
   is attached as sub-TLV of the corresponding Tunnels.

   If there is no tunnel between the ingress and egress nodes,
   Tunnel-Type = 16 (BARE) should be used.

Dunbar, et al.        Expires February 22, 2023          [Page 6]
Internet-Draft      AppMetaData for 5G EC Service

   If the AppMetaData is applicable to all tunnel types between
   the ingress and the egress nodes, Tunnel-Type = BARE can also
   be used.

   Note: attaching the AppMetaData to Tunnel Encap path attribute
   allow the AppMetaData applicable to different NLRIs.

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

  4.1. The Site Preference Index sub-TLV format

   The Site Preference Index is another factor integrated into
   the total cost for path selection. One Edge Cloud site can
   have fewer computing servers, less power, or lower internal
   network bandwidth than another. E.g., one micro edge computing
   center located at a remote cell site has less preference value
   than an edge site in a metro area that hosts management
   systems, analytics functions, and security functions.

   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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Site-Preference Sub-Type   |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Preference Index value                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    Figure 5: Preference Index Sub-TLV

   Preference Index value: 1-100, with 1 being least preferred,
   and 100 being the most preferred.

Dunbar, et al.        Expires February 22, 2023          [Page 7]
Internet-Draft      AppMetaData for 5G EC Service

  4.2. Capacity Index AppMetaData

   Capacity Index indicates the capacity value for a site or a
   pod where the edge services are hosted. One Edge Site can be
   in full capacity, or reduced capacity.

   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 (egress) router
   visible to the ingress routers can be running fine. Therefore,
   the ingress routers can't use BFD to detect the failures.

   When there is a failure occurring at an edge site (or pod),
   many instances can be impacted. In addition, the routes (i.e.,
   the IP addresses) in an Edge Cloud Site might not be
   aggregated nicely. 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.

   The Capacity Index can be attached as a sub-TLV under the
   Tunnel-Encap path attribute:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Capacity-SubType         |         Reserved              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Site-ID (2 octets)     |       Site Capacity           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  - Capacity subtype: (TBD by IANA)

  - Site ID: identifier for a group of routes whose capacity is
     indicated by the capacity value carried in the UPDATE. There
     could be more than one sites (or Pods) connected to the egress
     router (a.k.a. Edge DC GW)

Dunbar, et al.        Expires February 22, 2023          [Page 8]
Internet-Draft      AppMetaData for 5G EC Service

  - Site  Capacity:  represent  the  percentage  of  the  site
     availability, e.g., 100%, 50%, or 0%. When a site goes dark,
     the Index is set to 0.  50 means 50% capacity functioning.

4.2.1. Capacity Site Index attached to services

  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
  Index for every BGP Update message if there is no change to
  the site-reference identifier or the Capacity value for the
  service instances.

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

4.2.2. 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 without attaching any routes.

  When an ingress router receives a BGP Update message from
  Router-X with the Site-Capacity Sub-TLV without routes
  attached, the new Site-Capacity value is applied to all routes
  that have the Router-X as their next hops and are associated
  with the Site-ID in the Sub-TLV.

Dunbar, et al.        Expires February 22, 2023          [Page 9]
Internet-Draft      AppMetaData for 5G EC Service

  4.3. 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     subType=Aggregated-Cost   |               Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                   Measurement Period                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Aggregated Load Index to reach the App Server       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 2: Aggregated Load Index Sub-TLV

     Aggregated-Cost Sub-Type(TBD1): Aggregated Load Measurement
     Index to reach toe App Server, which is configured or
     calculated by the egress nodes.

   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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     subType= Raw-Measurements |               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

     Raw-Measurement Sub-Type (TBD2): Raw measurements of
     packets/bytes to/from the App Server address.

Dunbar, et al.        Expires February 22, 2023         [Page 10]
Internet-Draft      AppMetaData for 5G EC Service

     The receiver nodes can calculate the cost to reach the App
     server by a weighted combination of raw measurements sent
     from the App server, e.g.

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

     Where wi, which are configured by operators, is a value
     between 0 and 1; w1+ w2+ w3+ w4 = 1.

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

5. Consideration for Optimal Paths Selection

  When an ingress router 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, Site Preference, load index, and network cost.
  The Plugin function is called Cost Compute Engine throughout
  this document. When any of those factors goes to 0, the effect
  is the same as the egress router not reachable, which triggers
  the ingress nodes to switch to another egress router. But when
  any of those factors just degrade, the effect could be a path
  to another egress router becoming more optimal.

  Suppose a destination address for 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 (aa08::4450). The Cost
  Compute Engine can insert a higher weight for the tunnel
  associated with R1 for the prefix via the tunnel.

   For routes associated with a specific tunnel, the AppMetaData
   is attached as sub-TLV of the corresponding Tunnels.

   If there is no tunnel between the ingress and egress nodes,
   Tunnel-Type = 16 (BARE) should be used.

   If the AppMetaData is applicable to all tunnel types between
   the ingress and the egress nodes, Tunnel-Type = BARE can also
   be used.

Dunbar, et al.        Expires February 22, 2023         [Page 11]
Internet-Draft      AppMetaData for 5G EC Service

   Note: attaching the AppMetaData to Tunnel Encap path attribute
   allow the AppMetaData applicable to different NLRIs.

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.

   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

   The AppMetaData described in this document are only intended
   for propagating between Ingress and egress routers of one
   single BGP domain, i.e., the 5G Local Data Networks, which is
   a limited domain with edge services a few hops away from the
   ingress nodes. Only the selective services by UEs are
   considered as 5G Edge Services.  The 5G LDN is usually managed
   by one operator, even though the routers can be by different
   vendors.

9. Security Considerations

   The proposed AppMetaData sub-TLVs are advertised within the
   trusted domain of 5G LDN's ingress and egress routers. There
   are no extra security threats compared with iBGP.

Dunbar, et al.        Expires February 22, 2023         [Page 12]
Internet-Draft      AppMetaData for 5G EC Service

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

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>.

   [RFC7911] D. Walton, et al, "Advertisement of Multiple Paths
             in BGP", RFC7911, July 2016.

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

Dunbar, et al.        Expires February 22, 2023         [Page 13]
Internet-Draft      AppMetaData for 5G EC Service

  11.2. Informative References

   [3GPP TS 23.501]  3rd Generation Partnership Project;
             Technical Specification Group Services and System
             Aspects; System architecture for the 5G System (5GS)

   [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.

   [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.

   [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. Appendix A
 12.1. Example of Flow Affinity

   Here is one example to illustrate how Flow Affinity can be
   achieved. This illustration is an informational example.

   For the registered EC services, the ingress node keeps a table
   of

Dunbar, et al.        Expires February 22, 2023         [Page 14]
Internet-Draft      AppMetaData for 5G EC Service

   -  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-Edge-Sticky] 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 Cost 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, ingress router needs to select another path.

13. Acknowledgments

   Acknowledgements to Adrian Farrel, Robert Raszuk, Sue Hares,
   Donald Eastlake, Dhruv Dhody, and Cheng Li for their review
   and contributions.

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

Dunbar, et al.        Expires February 22, 2023         [Page 15]
Internet-Draft      AppMetaData for 5G EC Service

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

Dunbar, et al.        Expires February 22, 2023         [Page 16]