Network Working Group L. Dunbar Internet Draft H. Chen Intended status: Standard Futurewei Expires: April 26, 2021 October 26, 2020 OSPF extension for 5G Edge Computing Service draft-dunbar-lsr-5g-edge-compute-ospf-ext-00 Abstract This draft describes an OSPF extension that can dynamically adjust network forwarding behavior based on Application Servers' running status and environment. This feature can greatly improve latency and performance for 5G Edge Computing services. The extension enables a feature, called soft anchoring, which makes one Application Server at a specific location to be more preferred than others for the same application to receive packets 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 April 26, 2021 [Page 1] Internet-Draft OSPF Extension 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) 2020 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. Problem#1: ANYCAST in 5G Edge Computing Environment ....................................................... 5 1.3. Problem #2: Unbalanced Anycast Distribution due to UE Mobility............................................ 5 1.4. Problem 3: Application Server Relocation.......... 6 2. Conventions used in this document...................... 6 3. OSPF Extension for 5G EC............................... 8 3.1. Solution Overview................................. 8 Dunbar, et al. Expires April 26, 2021 [Page 2] Internet-Draft OSPF Extension for 5G EC Service 3.2. IP Layer Metrics to Gauge Application Behavior.... 9 3.3. To Equalize among Multiple ANYCAST Locations..... 10 3.4. OSPF Protocol Extension to advertise Load & Capacity.............................................. 11 3.5. Reason for using IGP Based Solution:............. 11 3.6. OSPF Extension Using TE Stub Link................ 12 3.7. Aggregated Link Cost Solution.................... 15 4. Soft Anchoring of an ANYCAST Flow..................... 16 5. Manageability Considerations.......................... 17 6. Security Considerations............................... 17 7. IANA Considerations................................... 18 8. References............................................ 18 8.1. Normative References............................. 18 8.2. Informative References........................... 18 9. Acknowledgments....................................... 19 1. Introduction This document describes an OSPF extension that can dynamically adjust network forwarding behavior towards Applications servers in 5G Edge Computing Environment based on the Application Servers running status and the UE (User Equipment) status. 1.1. 5G Edge Computing Background As described in [5G-EC-Metrics], one Application can have multiple Application Servers hosted in different Edge Computing data centers that are close in proximity. Those Edge Computing (mini) data centers are usually very close to, or co-located with, 5G base stations, with the goal to minimize latency and optimize the user experience. When a UE (User Equipment) initiates application packets using the destination address from a DNS reply or from its own cache, the 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 decapsulate the 5G GTP outer header and forwards the packets from the UEs to the Ingress router of the Edge Computing (EC) Local Data Network (LDN). The LDN for 5G EC, which is the IP Networks Dunbar, et al. Expires April 26, 2021 [Page 3] Internet-Draft OSPF Extension for 5G EC Service from 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) (gNB1), handover procedures are initiated and the 5G SMF (Session Management Function) also selects a new UPF-PSA. The standard handover procedures described in 3GPP TS 23.501 and TS 23.502 are followed. When the handover process is complete, the UE has a new IP address and the IP point of attachment is to the new UPF- PSA. 5GC may maintain a path from the old UPF to new the UPF for a short period of time for SSC [Session and Service Continuity] mode 3 to make the handover process more seamless. +--+ |UE|---\+---------+ +------------------+ +--+ | 5G | +---------+ | S1: aa08::4450 | +--+ | Site +--++---+ +----+ | |UE|----| A |PSA| 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 |PSA| Rb | | R2 | S2: aa08::4460 | +--+ | +--++----+ +----+ | +--+ | | +-----------+ | S3: aa08::4470 | |UE|---/+---------+ +------------------+ +--+ L-DN2 Figure 1: App Servers in different edge DCs Dunbar, et al. Expires April 26, 2021 [Page 4] Internet-Draft OSPF Extension for 5G EC Service 1.2. Problem#1: ANYCAST in 5G EC Environment Increasingly, Anycast is used extensively by various application providers and CDNs because ANYCAST makes it possible to dynamically load balance across server instances based on network conditions. Application Server location selection using Anycast address leverages the proximity information present in the network (routing) layer and eliminates the single point of failure and bottleneck at the DNS resolvers and application layer load balancers. Another benefit of using ANYCAST address is removing the dependency on UEs. Some UEs (or clients) might use their cached IP addresses instead of querying DNS for extended period. But, having multiple locations of the same ANYCAST address in 5G Edge Computing environment can be problematic because all those edge computing Data Centers can be close in proximity. There might be very little difference in the routing cost to reach the Application Servers in different Edge DCs. BGP is an integral part in the way IP Anycast usually functions. Within BGP routing there are multiple routes for the same IP address which are pointing to different locations. But many Edge DCs could be within one IGP domain, then there is no routing cost differentiation by BGP. Same routing cost to multiple ANYCAST locations can cause packets from one flow to be forwarded to different locations, which can cause service glitches. 1.3. Problem #2: Unbalanced Anycast Distribution due to UE Mobility Another problem of using ANYCAST address for multiple Application Servers of the same application in 5G environment is that UEs' frequent moving from one 5G site to another, which can make it difficult to plan where the App Server should be hosted. When one App server is heavily utilized, other App servers of the same address close-by can be very underutilized. Since the condition can be short Dunbar, et al. Expires April 26, 2021 [Page 5] Internet-Draft OSPF Extension for 5G EC Service lived, it is difficult for the application controller to anticipate the move and adjust. 1.4. Problem 3: Application Server Relocation When an Application Server is added to, moved, or deleted from a 5G Edge Computing Data Center, the routing protocol has to propagate the changes to 5G PSA or the PSA adjacent routers. After the change, the cost associated with the site [5G-EC-Metrics] might change as well. Note: for the 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 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 host 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 external IP network, in front of a set of application servers. From IP network Dunbar, et al. Expires April 26, 2021 [Page 6] Internet-Draft OSPF Extension for 5G EC Service perspective, this whole group of servers are 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 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. It might be co- located with 5G Base Station and not only host 5G core functions, but also host frequently used Edge server instances. gNB next generation Node B L-DN: Local Data Network PSA: PDU Session Anchor (UPF) SSC: Session and Service Continuity UE: User Equipment UPF: User Plane Function The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Dunbar, et al. Expires April 26, 2021 [Page 7] Internet-Draft OSPF Extension for 5G EC Service 3. OSPF Extension for 5G EC 3.1. Solution Overview From IP Layer, the Application Servers are identified by their IP (ANYCAST) addresses. The 5G Edge Computing controller or management system is aware of the ANYCAST addresses of the Applications that need optimized forwarding in 5G EC environment. The 5G Edge Computing controller or management system can configure the ACLs to filter out those applications on the routers adjacent to the 5G PSA and the routers to which the Application Servers are directly attached. The proposed solution is for the routers, i.e. A-ER, that have direct links, i.e. the stub links as described in RFC2328, 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). Dunbar, et al. Expires April 26, 2021 [Page 8] Internet-Draft OSPF Extension for 5G EC Service 3.2. IP Layer Metrics to Gauge Application Behavior There are many available network techniques and protocols to optimize forwarding or ensuring QoS for applications, such as DSCP/DiffServ, Traffic Engineered (TE) solutions, Segment Routing, etc. But the reality is that most application servers don't expose their internal logics to network operators. Their communications are generally encrypted. Most of them do not even respond to PING or ICMP messages initiated by routers or network gears. [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/bites 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 Capacity Index is used to differentiate the running environment of the application server. Some data centers can have hundreds, or thousands, of servers behind an Application Server's App Layer Load Balancer that is reachable from external world. Other data centers can have very small number of servers for the application server. "Capacity Index", which is a numeric number, is used to represent the capacity of the application server in a specific location. - Site preference index: [IPv6-StickyService] describes a scenario that some sites are more preferred for handling an application server than others for flows from a specific UE. Dunbar, et al. Expires April 26, 2021 [Page 9] Internet-Draft OSPF Extension for 5G EC Service 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 5G EC environment, the A-ER can be the gateway router to the EC DC where multiple Application servers' instance 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. To Equalize among Multiple ANYCAST Locations The main benefit of using ANYCAST is to leverage the network layer information to equalize the traffic among multiple Application Server locations of the same Application, which is identified by its ANYCAST addresses. For 5G Edge Computing environment, the ingress routers to the LDN needs 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. [5G-EC-Metrics] describes the algorithms that can be used by the routers directly attached to the 5G PSA to compare the cost to reach the App Servers between the Site-i or Site-j: alpha*(LoadIndex-i*Beta-i) (1-alpha)*(Delay-i*gamma-i) Cost=min(--------------- ---------- + -----------------------------) (LoadIndex-j * Beta-j) ( Delay-j *gamm-j) LoadIndex-i: weighted combination of the total bytes (or/and packets) sent to/received from the Application Server at Site-i during a fixed time period. Beta-i (larger value means higher capacity): capacity index at the site i. Delay-i: Network latency measurement (RTT) to the A-ER that has the Application Server attached at the site-i. Dunbar, et al. Expires April 26, 2021 [Page 10] Internet-Draft OSPF Extension for 5G EC Service gamma (larger value means higher preference): Network Preference index for the site-I. alpha (a value between 0 and 1: Weight for load & site Index. If smaller than 0.5, Network latency has more influence; otherwise, Server load has more influence). 3.4. OSPF Protocol Extension to advertise Load & Capacity Goal of the protocol extension: - Primary goal: Propagate the Load Measurement Index for the attached App Servers to other routers in the LDN. - Secondary goal: Propagate the Capacity Index & Site Preference Index to other routers in the LDN. Capacity index & Site preference might be steadier for an Application server in a data center. It is possible to use network management channel to distribute those two attributes. Therefore, it is the secondary goal. The OSPF extension takes the approach of TE solution: - Each mini-DC gateway router announces the stub networks of the attached Server addresses with the Load Index Sub- TLV. Only need to advertise the addresses for the applications that needs the network to optimize the forwarding. Therefore, A-ER do not need to advertise all attached subnets. - Load Index and Capacity Index are encoded in a Sub-TLV added to the LSA. 3.5. Reason for using IGP Based Solution: For scenario of multiple mini data centers within one AS domain, there are benefits of using IGP approach: - Intermediate routers can forward packets optimally because they can derive the load status for the Application Servers at different data centers by the IGP protocol, Dunbar, et al. Expires April 26, 2021 [Page 11] Internet-Draft OSPF Extension for 5G EC Service - the path to the expected destination may be more accurate or shorter - Can quickly converge on faulty links and routers - When a mini data center has failures, all the packets in the fly can be optimally forwarded to an App Server in another DC. - Doesn't need ingress node to establish tunnels with egress nodes. - The operations in this approach from users' point of view may be simpler. Drawback of using IGP: - This approach might not suit well to multiple ISPs networks. Using BGP, such as community extension or Tunnel Encap extension, approach may be better for the network crossing multiple ISPs. 3.6. OSPF Extension Using TE Stub Link A new link type in Link TLV of TE LSA is defined for the stub links, in addition to the existing P2P and Multi- Access link types. A Stub Link is the address to the Application Server attached. For a stub link, a Link TLV comprises a Link Type sub-TLV with stub link type, a Link ID sub-TLV with the address of the attached App Server (stub-link), Link Data Sub-TLV and some new sub-TLVs, such as, Load measurement sub-TLV, Capacity sub-TLV and Preference sub-TLV. An example of Link TLV for a stub link is illustrated below: Dunbar, et al. Expires April 26, 2021 [Page 12] Internet-Draft OSPF Extension for 5G EC Service 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 2 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link type sub-TLV for stub link | ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link ID sub-TLV for the Instance address | ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link data sub-TLV for the mask of the AppServer address | ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Load measurement sub-TLV | ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Capability sub-TLV | ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preference sub-TLV | ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Type value of the Link Type sub-TLV for the stub link: 3 (to be assigned by IANA). Note: [RFC3630] has specified: Type=1 for P2P and Type=2 used for Multiaccess. The Link Data Sub-TLV for the stub network is defined as: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AppServer IP address mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Dunbar, et al. Expires April 26, 2021 [Page 13] Internet-Draft OSPF Extension for 5G EC Service 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Load measurement Sub-TLV: Type=1: measurement of the packets towards the stub link (i.e. towards the server instance); Type=2: measurement of packets from the stub link (i.e. from the server instance). Measurement Period: A user specified period in seconds, default is 3600 seconds. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Dunbar, et al. Expires April 26, 2021 [Page 14] Internet-Draft OSPF Extension for 5G EC Service Note: "Capacity Index" and "Site preference" can be more stable for each site. If those values are configured to nodes, they might not need to be included in every OSPF LSA. 3.7. Aggregated Link Cost Solution Another solution is to reuse the field for link cost of a stub link. For a router with an Application Server directly attached, its router LSA can contain a stub link for the App Server's address [RFC2328]. This solution is using a formula to calculate the aggregated cost value to the directly attached App Server and assigned the cost value to the Metric field of the stub link in the LSA in RFC2328. The cost to the attached Application Server plays a significant role on where the flows should be routed. See Section 4 for soft anchoring a flow to a specific location when the UEs move. In this solution, the values of the Link ID, Link data and link cost for the stub link are as follows: - The Link ID is the IP address of the Application Server, - The Link Data is the network mask of the Application Server address, - The Link cost is the aggregated cost reach the attached Application Server. In this solution, every router connected to an Application Server MUST use the same formula to compute the cost of the Application Server. No new protocol code point is needed. The drawback of this solution is that Ingress router cannot make differentiated forwarding for different applications flows. Dunbar, et al. Expires April 26, 2021 [Page 15] Internet-Draft OSPF Extension for 5G EC Service 4. Soft Anchoring of an ANYCAST Flow This section describes a solution that can anchor an application flow from a UE to a specific ANYCAST instance even when the UE moves from one 5G Site to another. This is called "Sticky Service" in the 3GPP Edge Computing specification. Lets' 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. When there is failure at 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 failure. Here is details of this solution: - 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 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 higher cost, say 30. o ANYCAST L2 has the lowest cost when attached to R2, higher cost when attached to R1, R3, R4 respectively. o ANYCAST L3 has the lowest cost when attached to R3, higher cost when attached to R1, R2, R4 respectively, and Dunbar, et al. Expires April 26, 2021 [Page 16] Internet-Draft OSPF Extension for 5G EC Service 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 replies 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 replies the ANYCAST address G1, which has the same cost regardless 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 respond back 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. 5. Manageability Considerations To be added. 6. Security Considerations Dunbar, et al. Expires April 26, 2021 [Page 17] Internet-Draft OSPF Extension for 5G EC Service To be added. 7. IANA Considerations To be added. 8. References 8.1. 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 8.2. 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. Dunbar, et al. Expires April 26, 2021 [Page 18] Internet-Draft OSPF Extension for 5G EC Service [5G-StickyService] 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. 9. Acknowledgments Acknowledgements to Donald Eastlake for their review and contributions. This document was prepared using 2-Word-v2.0.template.dot. Dunbar, et al. Expires April 26, 2021 [Page 19] Internet-Draft OSPF Extension for 5G EC Service Authors' Addresses Linda Dunbar Futurewei Email: ldunbar@futurewei.com HuaiMo Chen Futurewei Email: huaimo.chen@futurewei.com Dunbar, et al. Expires April 26, 2021 [Page 20]