Network Working Group L. Dunbar Internet Draft Futurewei Intended status: Standard K. Majumdar Expires: June 10, 2022 CommScope H. Wang Huawei December 10, 2021 BGP Update for 5G Edge Computing Service Metadata draft-dunbar-idr-5g-edge-compute-app-meta-data-04 Abstract This draft describes a new AppMetaData subTLV carried by Tunnel Encap[RFC9012] Path Attribute for egress router to advertise the running status and environment for the directly attached 5G 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 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. xxx, et al. Expires June 10, 2022 [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) 2021 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 1.1. 5G Edge Computing Background......................... 3 1.2. 5G Edge Computing Network Properties................. 4 1.3. Problem#1: ANYCAST in 5G EC Environment.............. 6 1.4. Problem #2: Unbalanced Anycast Distribution due to UE Mobility.................................................. 7 1.5. Problem 3: Application Server Relocation............. 7 2. Conventions used in this document......................... 8 3. Usage of App-Meta-Data for 5G Edge Computing.............. 9 3.1. Assumptions.......................................... 9 Dunbar, et al. Expires June 10, 2022 [Page 2] Internet-Draft AppMetaData for 5G EC Service 3.2. IP Layer Metrics to Gauge Application Behavior....... 9 3.3. AppMetaData Constrained Optimal Path Selection...... 10 3.4. BGP Protocol Extension to advertise Load & Capacity. 11 3.5. Ingress Node BGP Path Selection Behavior............ 12 3.5.1. AppMetaData Influenced BGP Path Selection...... 12 3.5.2. Forwarding Behavior............................ 12 3.5.3. Forwarding Behavior after a UE moving to a new 5G Site.................................................. 13 4. The Sub-TLVs for App-Meta-Data........................... 14 4.1. Load Measurement sub-TLV format..................... 14 4.2. Capacity Index sub-TLV format....................... 15 4.3. The Site Preference Index sub-TLV format............ 16 5. AppMetaData Propagation Scope............................ 16 6. Metrics Change Rate Consideration........................ 16 7. Soft Anchoring of an ANYCAST Flow........................ 17 8. Manageability Considerations............................. 18 9. Security Considerations.................................. 19 10. IANA Considerations..................................... 19 11. References.............................................. 19 11.1. Normative References............................... 19 11.2. Informative References............................. 20 12. Acknowledgments......................................... 20 1. Introduction 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. 1.1. 5G Edge Computing Background In 5G Edge Computing (EC), one Application can be hosted on multiple Application Servers in different EC data centers that are close in proximity. The network connecting the EC data centers with the 5G Base stations consists of small number of routers dedicated for the 5G Local Data Network (LDN), to minimize latency and optimize the user experience. When a User Equipment (UE) initiates application packets using the destination address from a DNS reply or its cache, the Dunbar, et al. Expires June 10, 2022 [Page 3] Internet-Draft AppMetaData for 5G EC Service packets from the UE are carried in a PDU session through 5G Core [5GC] to the 5G UPF-PSA (User Plan Function - PDU Session Anchor). The UPF-PSA decapsulates the 5G GTP outer header and forwards the packets from the UEs to its directly connected Ingress router of the 5G LDN. The LDN for 5G EC, which is the IP Networks from the 5GC perspective, is responsible for forwarding the packets to the intended destinations. When the UE moves out of coverage of its current gNB (next- generation Node B)and anchors to a new gNB, the 5G SMF (Session Management Function) could select the same UPF or a new UPF for the UE per standard handover procedures described in 3GPP TS 23.501 and TS 23.502. If the UE is anchored to a new UPF-PSA when the handover process is complete, the packets to/from the UE is carried by a GTP tunnel to the new UPF-PSA. Per TS 23.501-h20 Section 5.8.2, the UE may maintain its IP address when anchored to a new UPF-PSA unless the new UFP-PSA belongs to different mobile operators. 5GC may maintain a path from the old UPF to the new UPF for a short time for the SSC [Session and Service Continuity] mode 3 to make the handover process more seamless. 1.2. 5G Edge Computing Network Properties In this document, 5G Edge Computing Network refers to multiple Local IP Data Networks (LDN) in one region that interconnect the Edge Computing data centers. Those IP LDN networks are the N6 interfaces from 3GPP 5G perspective. The ingress routers to the 5G Edge Computing Network are the routers directly connected to 5G UPFs. The egress routers to the 5G Edge Computing Network are the routers that have a direct link to the Edge Computing servers. The servers and the egress routers are co-located. Some of those Edge Computing Data centers may have Virtual switches or Top of Rack switches between the egress routers and the servers. But transmission delay between the egress routers and the Edge Computing servers is too small to be considered in this document. When one EC data center has multiple EC Servers attached to one App Layer Load Balancer, only the App Layer Load Balancer Dunbar, et al. Expires June 10, 2022 [Page 4] Internet-Draft AppMetaData for 5G EC Service is visible to the 5G Edge Computing Network. How the App Layer Load balancer manages the individual servers is out of the scope of the network layer. The 5G EC Services are specially managed services optimized by utilizing the network topology and multiple servers with the same IP address (ANYCAST) in multiple EC Data Centers. Many services by the UEs are not part of the registered 5G EC Services. +--+ |UE|---\+---------+ +------------------+ +--+ | 5G | +--------+ | S1: aa08::4450 | +--+ | Site +--+-+---+ +----+ | |UE|----| A |PSA1| Ra| | R1 | S2: aa08::4460 | +--+ | +----+---+ +----+ | +---+ | | | | | S3: aa08::4470 | |UE1|---/+---------+ | | +------------------+ +---+ |IP Network | L-DN1 |(3GPP N6) | | | | +------------------+ | UE1 | | | S1: aa08::4450 | | moves to | +----+ | | Site B | | R3 | S2: aa08::4460 | v | +----+ | | | | S3: aa08::4470 | | | +------------------+ | | L-DN3 +--+ | | |UE|---\+---------+ | | +------------------+ +--+ | 5G | | | | S1: aa08::4450 | +--+ | Site +--+--+---+ +----+ | |UE|----| B |PSA2| Rb | | R2 | S2: aa08::4460 | +--+ | +--+-+----+ +----+ | +--+ | | +-----------+ | S3: aa08::4470 | |UE|---/+---------+ +------------------+ +--+ L-DN2 Figure 1: App Servers in different edge DCs Dunbar, et al. Expires June 10, 2022 [Page 5] Internet-Draft AppMetaData for 5G EC Service 1.3. Problem#1: ANYCAST in 5G EC Environment Increasingly, Anycast is used by various application providers and CDNs because Anycast provides better and faster resiliency to failover events than GEO database DNS-based load balancing, which relies on DNS to provide a different IP based on source address. Anycast address leverages the proximity information present in the network (routing) layer. It eliminates the single point of failure and bottleneck at the DNS resolvers and application layer load balancers. Another benefit of using the ANYCAST address is removing the dependency on UEs. Some UEs (or clients) might use their cached IP addresses for an extended period instead of querying DNS. Client using Virtual IP address is a common practice in Cloud Native networking, e.g., Kubernetes, to scale dynamic changes of app servers' instantiations. However, Virtual IP requires the destination node to perform address translation for return traffic, which is unsuitable for underlay network nodes with millions of flows passing by. Having multiple locations of the same ANYCAST address in the 5G EC LDC can be problematic if path selection is solely based on routing cost as the difference in the routing cost to reach the Application Servers attached to different egress routers can be very small. This list elaborates the issues in detail: a) Path Selection: When a new flow comes to an ingress node (Ra), how to avoid instability with Anycast flipping between paths to the same address. The problem is more so with BGP multipath and picking the optimal path depending on close metrics. b) Ingress node forwards the packets from one flow to the same ANYCAST server. a.k.a. Flow Affinity, or Flow-based load balancing. Almost all vendors have supported flow or session based ECMP load balancing and not per packet to avoid out of order packets for decades. When a flow is hashed to an ECMP path, the flow remains on that path for the life of the flow until the flow ends. Dunbar, et al. Expires June 10, 2022 [Page 6] Internet-Draft AppMetaData for 5G EC Service The ingress node, (Ra/Rb), can use Flow ID (in IPv6 header) or UDP/TCP port number combined with the source address to enforce packets in one flow being placed in one tunnel to one Egress router. No new features are needed. c) When a UE moves to a new Cell Tower, a method is needed to stick the flow to the same ANYCAST server, which is required by 5G Edge Computing: 3GPP TR 23.748. Soft-Anchoring in Section 7 describes one method to achieve stickiness. [5g-edge-compute-sticky-service] describes several approaches to achieve stickiness in the IPv6 domain. From BGP perspective, the multiple servers with the same IP address (ANYCAST)attached to different egress routers is the same as multiple next hops for the IP address. This draft describes the BGP UPDATE to enable ingress routers to take the App Server load, the capacity index, and the location preference into consideration when computing the optimal path to egress routers. 1.4. Problem #2: Unbalanced Anycast Distribution due to UE Mobility UEs frequent moving from one 5G site to another can make it difficult to plan where and how many to deploy the App servers. When one App server is heavily utilized, other servers of the same App close-by can be very underutilized. Since the condition can be short-lived, it is difficult for the application controller to anticipate the move and adjust. 1.5. Problem 3: Application Server Relocation When an Application Server is added to, moved, or deleted from a 5G EC Data Center, the routing protocol needs to propagate the changes to 5G PSA or the PSA adjacent routers. After the change, the cost associated with the site might change as well. Dunbar, et al. Expires June 10, 2022 [Page 7] Internet-Draft AppMetaData for 5G EC Service Note: for ease of description, the Edge Application Server and Application Server are used interchangeably throughout this document. 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 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 Dunbar, et al. Expires June 10, 2022 [Page 8] Internet-Draft AppMetaData for 5G EC Service 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. Usage of App-Meta-Data for 5G Edge Computing 3.1. Assumptions From IP Layer, the Application servers are identified by their IP (ANYCAST) addresses. Here are some assumptions about the 5G EC services: - Only the registered EC services, which are only a small portion of the services, need to include the AppMetadata in path selection. - The 5G EC controller or management system push down the policies (e.g., ACLs) on the relevant routers to filter out those registered EC services. - The ingress routers' local BGP path compute algorithm includes a special plugin that can compute the path to the optimal Next Hop (egress router) based on the BGP AppMetaData TLV received for the registered EC services. The proposed solution is for the egress routers, i.e. A-ER, that have direct links to the Application Servers to collect various measurements about the Servers' running status [5G-EC- Metrics] and advertise the metrics to other routers in 5G EC LDN (Local Data Network). 3.2. IP Layer Metrics to Gauge Application Behavior Dunbar, et al. Expires June 10, 2022 [Page 9] Internet-Draft AppMetaData for 5G EC Service [5G-EC-Metrics] describes the IP Layer Metrics that can gauge the application servers running status and environment: - IP-Layer Metric for App Server Load Measurement: The Load Measurement to an App Server is a weighted combination of the number of packets/bytes to the App Server and the number of packets/bytes from the App Server which are collected by the A-ER to which the App Server is directly attached. The A-ER is configured with an ACL that can filter out the packets for the Application Server. - Capacity Index a numeric number, configured on all A-ERs in the domain consistently, is used to represent the capacity of the application server attached to an A-ER. At some sites, the IP address exposed to the A-ER is the App Layer Load balancer that have many instances attached. At other sites, the IP address exposed is the server instance itself. - Site preference index: is used to describe some sites are more preferred than others. For example, a site with higher bandwidth has a higher preference number than other. In this document, the term "Application Server Egress Router" [A-ER] is used to describe the last router that an Application Server is attached. For the 5G EC environment, the A-ER can be the gateway router to the EC DC where multiple Application servers are hosted. From IP Layer, an Application Server is identified by its IP (ANYCAST) Address. Those IP addresses are called the Application Server IDs throughout this document. 3.3. AppMetaData Constrained Optimal Path Selection The main benefit of using ANYCAST is to leverage the network layer information to select an optimal path among multiple application Server locations of the same application identified by its ANYCAST addresses. Dunbar, et al. Expires June 10, 2022 [Page 10] Internet-Draft AppMetaData for 5G EC Service For the 5G EC environment, the ingress routers to the LDN need to be notified of the Load Index and Capacity Index of the App Servers at different EC data centers to make the intelligent decision on where to forward the traffic for the application from UEs. Here is an algorithm that computes the cost to reach the App Servers attached to Site-i relative to another site, say Site- b. When the reference site, Site-b, is plugged in the formula, the cost is 1. So, if the formula returns a value less than 1, the cost to reach Site-i is less than reaching Site-b. CP-b * Load-i Pref-b * Network-Delay-i Cost-i= (w *(----------------) + (1-w) *(-------------------------)) CP-i * Load-b Pref-i * Network-Delay-b Load-i: Load Index at Site-i, it is the weighted combination of the total packets or/and bytes sent to and received from the Application Server at Site-i during a fixed time period. CP-i: capacity index at Site-i, a higher value means higher capacity. Delay-i: Network latency measurement (RTT) to the A-ER that has the Application Server attached at the site-i. Pref-i: Preference index for the Site-i, a higher value means higher preference. w: Weight for load and site information, which is a value between 0 and 1. If smaller than 0.5, Network latency and the site Preference have more influence; otherwise, Server load and its capacity have more influence. 3.4. BGP Protocol Extension to advertise Load & Capacity The goal of the protocol extension: - Propagate the Load Measurement Index for the attached App Servers to other routers in the LDN. - Propagate the Capacity Index, and Dunbar, et al. Expires June 10, 2022 [Page 11] Internet-Draft AppMetaData for 5G EC Service - Propagate Site Preference Index. The BGP extension is to include the Load Index Sub-TLV, Capacity Sub-TLV, and the Site Preference Sub-TLV in the Tunnel Encap Path Attribute associated with the routes. 3.5. Ingress Node BGP Path Selection Behavior 3.5.1. AppMetaData Influenced BGP Path Selection In this scenario, an ingress router will receive one ANYCAST address's multiple routes from different egress routers that have the direct links to the ANYCAST servers. The ingress router's BGP engine will do path selection, select the best route, and download to FIB. And BGP engine will also download the other paths to FIB that with the AppMetaData taken into the consideration. Assume that both Ra and Rb in Figure-1 have BGP Multipath enabled. As a result, Dst Address: S1:aa08::4450 is resolved via multiple NextHop: R1, R2, R3. Suppose the local BGP special Plugin for AppMetaData finds R1 is the best for the flow towards S1:aa08::4450. Then this special Plugin can insert a higher weight for the path R1 so that BGP Best Path is locally influenced by the weight parameter based on the local decision. 3.5.2. Forwarding Behavior When the ingress router receives a packet and lookup the FIB, it gets the destination prefix's whole path and AppMetaData. The Forwarding Plane will do computing for the packet and choose the suitable path as the result of the computing. Then the Forwarding Plane 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. 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. Dunbar, et al. Expires June 10, 2022 [Page 12] Internet-Draft AppMetaData for 5G EC Service For the registered EC services, the ingress node keeps a table of - Service ID (i.e., ANYCAST 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 (ANYCAST 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 computes the optimal path to an egress (NextHop) with the AppMetaData taken into consideration. The forwarding plane encapsulates the packet with a tunnel to the chosen egress (NextHop). The chosen NextHop and the Flow ID are recorded in the table entry of the EC Service ID. When the selected optimal egress router is no longer reachable, refer to Section 6 Soft Anchoring on how another path is selected. 3.5.3. Forwarding Behavior after a UE moving to a new 5G Site 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. When the new eNB is anchored to a different UPF, the packets from the UE traverse a different ingress router. If the UE source IP address has been changed, indicating the new UPF Dunbar, et al. Expires June 10, 2022 [Page 13] Internet-Draft AppMetaData for 5G EC Service might belongs to a different administrative domain, the new ingress router treats the packets from the UE as a new flow and select the optimal path based on the configured policies. If the UE maintains the same IP address when anchored to a new UPF, the directly connected ingress router might use the pre- computed Egress Router which is passed from the neighboring router. [5G-Edge-Sticky] describes the method for the ingress router connected to the UPF in the new site to take into consideration the information passed from other ingress routers in selecting the optimal paths. The detailed algorithm is out of the scope of this document. 4. The Sub-TLVs for App-Meta-Data The App-Meta-Data 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 Dunbar, et al. Expires June 10, 2022 [Page 14] Internet-Draft AppMetaData for 5G EC Service 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 5: 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. 4.2. Capacity Index sub-TLV format The Capacity 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 (TBD3) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Capacity Index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Dunbar, et al. Expires June 10, 2022 [Page 15] Internet-Draft AppMetaData for 5G EC Service Note: "Capacity 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. 4.3. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 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. 5. 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 ACLs need to receive the AppMetaData for specific services. 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. 6. Metrics Change Rate Consideration As the metrics change can impact the path selection, it is recommended to control the update frequency to avoid rapid route oscillations. Dunbar, et al. Expires June 10, 2022 [Page 16] Internet-Draft AppMetaData for 5G EC Service 7. Soft Anchoring of an ANYCAST Flow "Sticky Service" in the 3GPP Edge Computing specification (3GPP TR 23.748) is about flows from a UE sticking to a specific ANYCAST location when the UE moves from one 5G Site to another. "Soft Anchoring" is a mechanism for ingress routers to apply preference to the path towards the previous server location when the UE is anchored to a new UPF and continue using its cached IP for the App server. Let's assume one application "App.net" is instantiated on four servers that are attached to four different routers R1, R2, R3, and R4 respectively. It is desired for packets to the "App.net" from UE-1 to stick with one server, say the App Server attached to R1, even when the UE moves from one 5G site to another. However, when there is a failure reaching R1 or the Application Server attached to R1, the packets of the flow "App.net" from UE-1 need to be forwarded to the Application Server attached to R2, R3, or R4. We call this kind of sticky service "Soft Anchoring", meaning that anchoring to the site of R1 is preferred, but other sites can be chosen when the preferred site encounters a failure. Here are the detailed steps: - Assign a group of ANYCAST addresses to one application. For example, "App.net" is assigned with 4 ANYCAST addresses, L1, L2, L3, and L4. L1/L2/L3/L4 represents the location preferred ANYCAST addresses. - For the App.net Server attached to a router, the router has four Stub links to the same Server, L1, L2, L3, and L4 respectively. The cost to L1, L2, L3, and L4 is assigned differently for different egress routers. For example, o When attached to R1, the L1 has the lowest cost, say 10, when attached to R2, R3, and R4, the L1 can have a higher cost, say 30. o ANYCAST L2 has the lowest cost when attached to R2, higher cost when attached to R1, R3, R4 respectively. Dunbar, et al. Expires June 10, 2022 [Page 17] Internet-Draft AppMetaData for 5G EC Service o ANYCAST L3 has the lowest cost when attached to R3, higher cost when attached to R1, R2, R4 respectively, and o ANYCAST L4 has the lowest cost when attached to R4, higher cost when attached to R1, R2, R3 respectively - When a UE queries for the "App.net" for the first time, the DNS reply has the location preferred ANYCAST address, say L1, based on where the query is initiated. - When the UE moves from one 5G site-A to Site-B, UE continues sending packets of the "App.net" to ANYCAST address L1. The routers will continue sending packets to R1 because the total cost for the App.net instance for ANYCAST L1 is lowest at R1. If any failure occurs making R1 not reachable, the packets of the "App.net" from UE-1 will be sent to R2, R3, or R4 (depending on the total cost to reach each of them). If the Application Server supports the HTTP redirect, more optimal forwarding can be achieved. - When a UE queries for the "App.net" for the first time, the global DNS reply has the ANYCAST address G1, which has the same cost regardless of where the Application servers are attached. - When the UE initiates the communication to G1, the packets from the UE will be sent to the Application Server that has the lowest cost, say the Server attached to R1. The Application server is instructed with HTTPs Redirect to reply with a location-specific URL, say App.net-Loc1. The client on the UE will query the DNS for App.net-Loc1 and get the response of ANYCAST L1. The subsequent packets from the UE-1 for App.net are sent to L1. 8. Manageability Considerations To be added. Dunbar, et al. Expires June 10, 2022 [Page 18] Internet-Draft AppMetaData for 5G EC Service 9. Security Considerations To be added. 10. IANA Considerations Here are new Sub-TLV types requiring IANA registration: 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: Capacity value sub-TLV Type = TBD4: Site preference 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, . [RFC8200] s. Deering R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", July 2017 Dunbar, et al. Expires June 10, 2022 [Page 19] Internet-Draft AppMetaData for 5G EC Service 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-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. [BGP-SDWAN-Port] L. Dunbar, H. Wang, W. Hao, "BGP Extension for SDWAN Overlay Networks", draft-dunbar-idr-bgp- sdwan-overlay-ext-03, work-in-progress, Nov 2018. [SDWAN-EDGE-Discovery] L. Dunbar, S. Hares, R. Raszuk, K. Majumdar, "BGP UPDATE for SDWAN Edge Discovery", draft-dunbar-idr-sdwan-edge-discovery-00, work-in- progress, July 2020. [Tunnel-Encap] E. Rosen, et al "The BGP Tunnel Encapsulation Attribute", draft-ietf-idr-tunnel-encaps-10, Aug 2018. 12. Acknowledgments Acknowledgements to Donald Eastlake for their review and contributions. Dunbar, et al. Expires June 10, 2022 [Page 20] Internet-Draft AppMetaData for 5G EC Service This document was prepared using 2-Word-v2.0.template.dot. Authors' Addresses Linda Dunbar Futurewei Email: ldunbar@futurewei.com Kausik Majumdar CommScope 350 W Java Drive, Sunnyvale, CA 94089 Email: kausik.majumdar@commscope.com Haibo Wang Huawei Email: rainsword.wang@huawei.com Gyan Mishra Verizon Email: gyan.s.mishra@verizon.com Dunbar, et al. 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