Network Working Group L. Dunbar Internet Draft Futurewei Intended status: Standard K. Majumdar Expires: March 19, 2023 Microsoft H. Wang Huawei G. Mishra Verizon September 19, 2022 BGP Extension for 5G Edge Service Metadata draft-dunbar-idr-5g-edge-service-metadata-02 Abstract This draft describes three new sub-TLVs for egress routers to advertise the Edge Service Metadata of the directly attached edge services (ES). The Edge Service Metadata 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 March 19, 2023 [Page 1] Internet-Draft BGP extension for 5G Edge Services 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 for Edge Service Metadata.......... 5 3.1. Ingress Node BGP Path Selection Behavior............. 5 3.1.1. Edge Service Metadata 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. Edge Service Metadata Encoding............................ 6 4.1. Metadata Path Attribute.............................. 6 4.2. The Site Preference Index sub-TLV format............. 7 Dunbar, et al. Expires March 19, 2023 [Page 2] Internet-Draft BGP extension for 5G Edge Services 4.3. Capacity Index Metadata.............................. 8 4.3.1. Capacity Site Index attached to services........ 9 4.3.2. BGP UPDATE with standalone Capacity Site Index.. 9 4.4. Load Measurement sub-TLV format..................... 10 5. Service Metadata Influenced Decision Process............. 11 6. Edge Service Metadata 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. Appendix A.............................................. 15 12.1. Example of Flow Affinity........................... 15 13. Acknowledgments......................................... 16 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 a new Metadata Path Attribute and three new sub-TLVs for egress routers to advertise the Edge Service Metadata of the directly attached edge services. The Edge Service Metadata in this document refers to edge services' site capacity, the site preference, and the load index, which are further explained in Section 3. Note: the proposed Edge Service Metadata are not intended for the services reachable via the networks outside the 5G LDN. The Edge Service Metadata 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 a single domain with RR controlling the propagation of the BGP UPDATE. The Edge Service Metadata is only attached to the services (routes) hosted in the 5G edge cloud sites, which are only a small Dunbar, et al. Expires March 19, 2023 [Page 3] Internet-Draft BGP extension for 5G Edge Services subset of services initiated from UEs. E.g., not for UEs accessing many internet sites. 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 Dunbar, et al. Expires March 19, 2023 [Page 4] Internet-Draft BGP extension for 5G Edge Services 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 for Edge Service Metadata The goal of the BGP extension is for egress routers to propagate the metrics about their running environment to ingress routers, which are call the Edge Service Metadata throughout the document. Here are some examples of the metrics propagated by the egress routers: - The site Capacity Index, - The Site Preference Index, - The Load Measurement Index for the attached edge services. This section specifies how those Metadata impact the ingress nodes' path selections. 3.1. Ingress Node BGP Path Selection Behavior 3.1.1. Edge Service Metadata 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 an Edge Service Management function that can select paths based on the Edge Service Metadata received. [5G-EC-Metrics] has an example algorithm to compute the weighted path cost based on the Edge Service Metadata carried by the sub-TLVs specified in this document. Section 5 has the detailed description of the Edge Service Metadata influenced optimal path selection. 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. Dunbar, et al. Expires March 19, 2023 [Page 5] Internet-Draft BGP extension for 5G Edge Services 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. Edge Service Metadata Encoding 4.1. Metadata Path Attribute The Metadata Path Attribute is an optional transitive BGP Path attribute to carry the Edge Service Metadata described in this document. Will need IANA to assign a value as the Type code of the Path Attribute. The Metadata Path Attribute, illustrated below, consists of a set of sub-TLVs, with each sub-TLV containing the information corresponding to a specific metrics of the Edge Service Metadata. Dunbar, et al. Expires March 19, 2023 [Page 6] Internet-Draft BGP extension for 5G Edge Services 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service-Metadata Type | Length (2 Octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Value (multiple Metadata sub-TLVs) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Edge Service Metadata Path Attribute Service-Metadata Path Attribute Type (2 octets): identify the Metadata Path Attribute, to be assigned by IANA. o Length (2 octets): the total number of octets of the value field. o Value (variable): comprised of multiple sub-TLVs. There are three types of Edge Service Metadata sub-TLVs specified by this document for the Capacity Index Value, the Site Preference Index Value, and the Load Measurement. All values in the Sub-TLVs are unsigned 32 bits integers. 4.2. The Site Preference Index sub-TLV format The Site Preference Index is one of the factors 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 index 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 2: Preference Index Sub-TLV Dunbar, et al. Expires March 19, 2023 [Page 7] Internet-Draft BGP extension for 5G Edge Services Preference Index value: 1-100, with 1 being the least preferred, and 100 being the most preferred. 4.3. Capacity Index Metadata 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, reduced capacity, or completely out of service. 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 sub-TLV: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: Capacity Index Sub-TLV - Capacity subtype: (TBD by IANA) Dunbar, et al. Expires March 19, 2023 [Page 8] Internet-Draft BGP extension for 5G Edge Services - 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) - 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. 4.3.1. 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. 4.3.2. 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 March 19, 2023 [Page 9] Internet-Draft BGP extension for 5G Edge Services 4.4. 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 Edge Service 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 Edge Service | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: Aggregated Load Index Sub-TLV Aggregated-Cost Sub-Type(TBD1): Aggregated Load Measurement Index to reach the Edge Service, 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 Edge Service | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | total number of packets from the Edge Service | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | total number of bytes to the Edge Service | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | total number of bytes from the Edge Service | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: Raw Load Measurement Sub-TLV Raw-Measurement Sub-Type (TBD2): Raw measurements of packets/bytes to/from the Edge Service address. Dunbar, et al. Expires March 19, 2023 [Page 10] Internet-Draft BGP extension for 5G Edge Services The receiver nodes can calculate the cost to reach the Edge Service by a weighted combination of raw measurements sent from the Edge Service, 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. Service Metadata Influenced Decision Process 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 services configured to be influenced by the Edge Service Metadata, the ingress router's BGP Decision process would trigger the Edge Service Management function to compute the weight to be applied to the route's next hop in the forwarding plane. The decision process is influenced by the Edge Service Metadata associated with the client routes, such as Site-Capacity-Index, Site Preference, and Load Index, in addition to the traditional BGP multipath computation algorithm, such as the Weight, Local preference, Origin, MED, etc., shown below: BGP ANYCAST Update +--------+ with Metadata +---------------+ | BGP |----------------->| EdgeServiceMgn| |Decision|< - - - - - - - - | | +---^-|--+ +-------|-------+ | | BGP ANYCAST | Update Anycast | | Route | Route Nexthops | | Multi-path NH install | with weight +---|-V--+ | | RIB | | +----+---+ | | | +---V------------------------------V-------+ | Forwarding Plane | | | +------------------------------------------+ Figure 6: Metadata Influenced Decision Dunbar, et al. Expires March 19, 2023 [Page 11] Internet-Draft BGP extension for 5G Edge Services When any of those metadata value goes to 0, the effect is the same as the routes becoming ineligible via the egress router who originates the metadata UPDATE. But when any of those metadata just degrade, there is possibility, even though smaller, for the egress router to continue as the optimal next hop. Suppose a destination address for aa08::4450 can be reached by three next hops (R1, R2, R3). Further, suppose the local BGP's Decision Process based on the traditional network layer policies & metrics identifies the R1 as the optimal next hop for this destination (aa08::4450). The Edge Service Metadata might result in R2 as the optimal next hop for the prefix and influence the Forwarding Plane. The Edge Service Metadata influencing next hop selection is different from the metric (or weight) to the next hop. The metric to a next hop can impact many (sometimes, tens of thousands) routes that have the node as their next hop. while as the Edge Service Metadata only impact the optimal next hop selection for a subset of client routes that are identified as the edge services. When the BGP custom decision [idr-custom-decision] is used, the Edge Service Management function would have algorithm to combine the Edge Service Metadata attributes with the custom decision to derive the optimal next hop for the Edge service routes. Note: For a BGP UPDATE message that only includes the Edge Service Path Attribute without any NLRI, the Site Capacity Index value is applied to all the NLRIs with the Site-ID indicated in the Edge Service Metadata Path Attribute. 6. Edge Service Metadata Propagation Scope Edge Service Metadata 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 Edge Service Metadata for specific Service IDs. For each registered Edge Service, a corresponding filter group can be formed on RR to represent the interested ingress routers that are interested in receiving the corresponding Edge Service Metadata information. Dunbar, et al. Expires March 19, 2023 [Page 12] Internet-Draft BGP extension for 5G Edge Services 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 Edge Service Metadata 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 Edge Service Metadata are advertised within the trusted domain of 5G LDN's ingress and egress routers. There are no extra security threats compared with iBGP. 10. IANA Considerations Need IANA to assign the Metadata Path Attribute Type. Metadata Path Attribute Type = TBD1. Need IANA to assign three new Sub-TLV types under the Metadata Path Attribute: Type = TBD2: Site preference value sub-TLV Type = TBD3: Site Capacity Index sub-TLV Dunbar, et al. Expires March 19, 2023 [Page 13] Internet-Draft BGP extension for 5G Edge Services Type = TBD4: Aggregated Load Measurement Index derived from the Weighted combination of bytes/packets sent to/received from the Edge Service address. Type = TBD5: Raw measurements of packets/bytes to/from the Edge Service address. 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, . [RFC7911] D. Walton, et al, "Advertisement of Multiple Paths in BGP", RFC7911, July 2016. 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. Dunbar, et al. Expires March 19, 2023 [Page 14] Internet-Draft BGP extension for 5G Edge Services [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. [IDR-CUSTOM-DECISION] A. Retana, R. White, "BGP Custom Decision Process", draft-ietf-idr-custom-decision- 08, Feb 2017. [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 - 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: Dunbar, et al. Expires March 19, 2023 [Page 15] Internet-Draft BGP extension for 5G Edge Services - 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 path 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, Alvaro Retana, 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 March 19, 2023 [Page 16] Internet-Draft BGP extension for 5G Edge Services 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 Contributors' Addresses Cheng Li Huawei Email: c.l@huawei.com Dunbar, et al. Expires March 19, 2023 [Page 17]