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Versions: 00 01                                                         
SPRING Working Group                                               C. Li
Internet-Draft                                                     Z. Li
Intended status: Informational                                   H. Yang
Expires: October 2, 2021                             Huawei Technologies
                                                          March 31, 2021


               IPv6-based Cloud-Oriented Networking (CON)
                    draft-li-rtgwg-ipv6-based-con-01

Abstract

   This document describes the scenarios, requirements and technologies
   for IPv6-based Cloud-oriented Networking.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 2, 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
   (https://trustee.ietf.org/license-info) in effect on the date of
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   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.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Underlay  . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Overlay . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  IPv6-based Cloud-Oriented Networking  . . . . . . . . . . . .   6
     4.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   7
       4.1.1.  Quick Connection  . . . . . . . . . . . . . . . . . .   7
       4.1.2.  Hybrid Network Connection . . . . . . . . . . . . . .   7
       4.1.3.  Path Programming  . . . . . . . . . . . . . . . . . .   7
       4.1.4.  Resource Assurance  . . . . . . . . . . . . . . . . .   8
       4.1.5.  Deterministic Delay . . . . . . . . . . . . . . . . .   8
       4.1.6.  Service Function Chaining . . . . . . . . . . . . . .   8
       4.1.7.  Performance Measurement . . . . . . . . . . . . . . .   9
       4.1.8.  Reliability . . . . . . . . . . . . . . . . . . . . .   9
       4.1.9.  Security  . . . . . . . . . . . . . . . . . . . . . .   9
       4.1.10. Forwarding Efficiency . . . . . . . . . . . . . . . .   9
       4.1.11. Application-Aware Networking  . . . . . . . . . . . .  10
     4.2.  Solutions . . . . . . . . . . . . . . . . . . . . . . . .  10
       4.2.1.  VPN . . . . . . . . . . . . . . . . . . . . . . . . .  10
       4.2.2.  Path Programming  . . . . . . . . . . . . . . . . . .  11
       4.2.3.  Service Function Chaining . . . . . . . . . . . . . .  11
       4.2.4.  IPv6 based Network Slicing  . . . . . . . . . . . . .  11
       4.2.5.  IPv6-based On-path Measurement  . . . . . . . . . . .  12
       4.2.6.  Reliability . . . . . . . . . . . . . . . . . . . . .  13
       4.2.7.  Security  . . . . . . . . . . . . . . . . . . . . . .  14
       4.2.8.  IPv6 Forwarding Efficiency  . . . . . . . . . . . . .  14
       4.2.9.  Application-aware IPv6 Networking . . . . . . . . . .  15
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  16
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  16
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   With the development of cloud computing, increasing services have
   been migrated from enterprises to cloud data centers.  Compared with
   interconnections between branches and headquarters, new connections
   between enterprise sites to cloud data centers and inter-cloud are
   added, which bring new requirements and challenges for existing
   networks.



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   When enterprises have workloads & applications & data split among
   different data centers, especially for those enterprises with
   multiple sites that are already interconnected by VPNs (e.g., MPLS
   L2VPN/L3VPN), challenges are introduced.
   [I-D.ietf-rtgwg-net2cloud-problem-statement] describes the problems
   that enterprises face today when interconnecting their branch offices
   with dynamic workloads in third party data centers (a.k.a.  Cloud
   DCs).

   SD-WAN is a flexible WAN architecture that enables flexible network-
   to-cloud and inter-clouds connections.  It supports to use
   alternative paths like internet or 4G / 5G connection instead of
   expensive MPLS leased lines to exchange data between sites and
   clouds.  However, when a WAN path travels multiple MPLS domains, the
   configurations are complicated due to multiple services touch points
   need to be configured.  Therefore, it is hard to support end-to-end
   path programming in IPv4/MPLS based SD-WAN.

   When using VXLAN in SD-WAN, only the overlay path or anchor points
   can be specified while the underlay forwarding path can not be
   specified.  Therefore, strict TE requirements like deterministic
   delay, specified path forwarding can not be satisfied.

   In order to resolve these challenges, this document propose
   IPv6-based Cloud-Oriented Networking (CON).  In addition, it
   describes the challenges for existing networks when clouds and
   networks are converged, requirements that IPv6-based CON should
   satisfy, and the solutions in IPv6-based CON that satisfy the
   requirements.

   IPv6-based CON supports quick and flexible connections between sites
   and clouds and inter-clouds, it also supports end-to-end path
   programming, which can be used for many use cases, such as strict
   path traffic engineering, deterministic delay forwarding, and service
   function chaining, to provide better network services for cloud-
   network and inter-cloud interconnections.

2.  Terminology

   This document makes use of the terms defined in [RFC8754] and
   [RFC8200], and the reader is assumed to be familiar with that
   terminology.  This document introduces the following terms:

   POP: Point of Presence

   CON: Cloud-Oriented Networking.

   EC: Edge Computing.



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   EDC: Edge Data center

   RDC: Regional Data Center

   CDC: Core Data Center

2.1.  Requirements Language

   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.  Problem Statement

   As development of cloud, many clouds have been deployed, such as
   Private cloud, Public Cloud, and Hybrid Cloud.  The cloud services
   can be provided by a third party, such as an OTT (Over-The-Top)
   content provider, and it can be provided by a network operator as
   well.  Furthermore, cloud can be deployed not only in IT data centers
   but also CT data centers.

   With the development and successful application of cloud native
   design in the IT field and Network Functions Virtualization (NFV)
   technologies, virtualization and cloudification have gradually
   matured and evolved to provide a new level of productivity, offering
   a new approach to telecom network construction.  Building cloud-based
   telecom networks (also known as telco clouds) becomes a new way of
   telecom network construction.

   In order to support low latency communication, the request should be
   responded at the near cloud data center, therefore edge computing
   data center (a.k.a Edge Cloud) is introduced.  Telecommunication
   services and third-party OTT services can be deployed in the edge
   cloud.

   As the deployment of clouds, the traffic pattern in the network has
   changed significantly, which results in new challenges for existing
   networks.

3.1.  Underlay

   From the aspect of underlay, cloud services requires the network to
   provide quick and flexible connection.

   The typical topology of telco cloud is shown in figure 1.




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                 +++++++        +++++++            ++++++
                 | EDC |        | RDC |            | CDC|
                 +++++++        +++++++            ++++++
                    |   *********  |   ************  |
                    |   *       *  |   *          *  |
      OLT/CSG/CPE---PE--* Metro *--PE--* Backbone *--PE--IGW---Internet
                        *       *      *          *
                        *********      ************

               Figure 1.Typical topology of telco cloud


   The edge cloud is deployed in edge data center (EDC) in the access
   network usually, so that the servers in the edge cloud can respond to
   the delay-sensitive requests rapidly, like 5G URLLC traffic.  The
   traffic is not delay-sensitive can be responded in regional cloud DC,
   which is located in the metro or core network.  Most cloud services
   may be deployed in the core cloud DC considering reducing the cost,
   which is far from the end user.  Like, the UPF may locate in the
   regional cloud DC or Core cloud DC, so that it can support more
   users.

   The traffic from end users to cloud servers are forwarded along with
   different paths due to the different locations of the end users and
   the cloud servers.

   In addition, when deploying new services, for instance, deploying a
   leased line from an enterprise site to a cloud data center, it will
   take probably weeks in the current IPv4/MPLS carrier network.
   Because the VPN configuration is needed to be done at multiple PE
   nodes if the leased line travels multiple domains (when using Option
   A between domains).  Also, the cloud operator needs to negotiate with
   network operators if the cloud services and the network services are
   provided by different operators.  For example, thousands of chain
   stores such as grocery stores or super markets are needed to connect
   to their enterprise VPNs, and they may use the cloud services.
   However, in IPv4/MPLS network, it may take weeks to establish a new
   VPN connection from a site to headquarter or cloud tenant networks.

   Furthermore, different traffic of different enterprise/tenant/users
   are treated differently in clouds, and they MAY be forwarded along
   with different service function chains (SFC).  However, it is hard to
   support SFC in IPv4 or MPLS based network in carrier's networks or
   data center networks.  Normally, to support SFC, the traffic steering
   policies are configured at multiple nodes along the SFC path, which
   is complicated.





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3.2.  Overlay

   In order to provide quick and flexible cloud connection, overlay
   connection is provided by cloud providers, especially the OTT cloud
   providers.

   SD-WAN is a typical fabric for DCI connection between clouds and
   sites, which provides a cheaper and smarter WAN connection.  Many SD-
   WAN providers builds their own WAN backbone network by connecting
   their POP GWs to provide better SLA assurance for tenants.  The
   typical topology of SD-WAN with POP GWs is shown in figure 2.



     Site CPE1--POP GW1 --------------------------POP GW2---Site CPE2
                   |                                 |
                   |          SD-WAN Backbone        |
                   |                                 |
       Cloud1---POP GW3---------------------------POP GW4--Cloud2

                 Figure 2. Typical topology of SD-WAN


   Currently, the traffic from the CPE to POP GW is forwarded through
   the shortest forwarding path over the Internet, or an MPLS tunnel.

   In addition, traffic from POP GW to another POP GW can be forwarded
   along with the MPLS tunnel that is a leased line, or over the
   internet, depending on the forwarding policies.

   When the traffic is forwarded over the internet, it can be forwarded
   over a VXLAN tunnel.  However, when using VXLAN, only the overlay
   connection is provided to enterprises/tenants, while the underlay
   forwarding path can not be specified and programmed.  Therefore the
   SLA requirements can not be guaranteed when the traffic is forwarded
   overlay.

4.  IPv6-based Cloud-Oriented Networking

   This document describes a networking architecture called IPv6-based
   Cloud-Oriented Networking (CON).  IPv6-based CON is an IPv6-based
   networking which provide quick, flexible connection to support
   dynamic site to cloud, and inter-cloud connections.  Also, it
   supports end-to-end underlay forwarding path programming, so that
   services like strict path TE and SFC can be supported better.

   The following section describes the requirements in IPv6-based CON,
   and the related solutions that meet the requirements.



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4.1.  Requirements

   This section describes the overall requirements which need to be
   fulfilled by IPv6-based Cloud-Oriented Networking.

4.1.1.  Quick Connection

   Enterprise sites can locate at any location around the world, they
   need to connect to the clouds or other sites in any time, from any
   where.  Also, enterprises may have some Virtual Private Clouds (VPC)
   in different clouds, they need to connect to each other in real time
   as well.  The servers may locate in different cloud data centers or
   enterprise sites, which provide services for employees or other
   users.  Therefore quick connection is required in IPv6-based CON.

4.1.2.  Hybrid Network Connection

   The enterprise VPN traffic can be forwarded around the world, which
   may travel heterogeneous networks, such as IPv4, MPLS and IPv6.

   Typically, when a SD-WAN network connects multiple sites and clouds,
   it may cover hybrid networks.  For example, the sub-path from the CPE
   to POP WG could be an IPv4 sub-path without any resource guarantee.
   The sub-path between POP GWs could be an MPLS LSP with resource
   reservation.

   Therefore, connection over hybrid networks MUST be supported in
   IPv6-based CON.

4.1.3.  Path Programming

   When the enterprise VPN traffic is forwarded among sites or clouds,
   it may be forwarded along different paths.  Each path has different
   performance such as different bandwidth, delay, etc.  For instance,
   path A is the shortest path from site 1 to cloud 1, which has the
   lowest delay, while the path B can provide more bandwidth than path
   A.  Therefore, the delay-sensitive traffic like PC gaming traffic
   SHOULD be forwarded along with path A, and the traffic that is delay-
   insensitive but requiring large bandwidth SHOULD be forwarded along
   with path B.

   In order to meet the different SLA requirements, IPv6-based CON MUST
   support path programming.








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4.1.4.  Resource Assurance

   In RSVP-TE MPLS, resources like bandwidth can be reserved for an LSP.
   When the traffic is forwarded along the LSP, the bandwidth can be
   guaranteed, which makes sure that the traffic will not be affected by
   other traffic.  In order to provide SLA guaranteed services,
   IPv6-based CON MUST support Resource Assurance.

   Network slicing is an approach to provide separate and independent
   end-to-end logical network over the physical network infrastructure.
   Each Network Slicing has its own resources, which can meet the
   specific SLA requirements.  In order to provide SLA guaranteed
   services, IPv6-based CON MUST support network slicing.

4.1.5.  Deterministic Delay

   Delay-sensitive traffic has the strict requirements of network delay.
   Especially, when the servers moved to clouds instead of locating
   locally within the enterprise site, the long physical distance of
   packet forwarding path will introduce larger delay.  In the
   traditional network, the shortest forwarding path is calculated based
   on the metric, and the metric is usually associated to the physical
   hops instead of latency.  However, minimum delay forwarding is
   required for delay-sensitive traffic, like real-time video broadcast
   and video meeting.

   Therefore, IPv6-based CON MUST have the capability to support path
   computing based on delay.  Also, it MUST be able to provide
   deterministic delay forwarding.

4.1.6.  Service Function Chaining

   Service Function Chaining [RFC7665] is a mechanism to provide
   different value-added services (VAS) for packets.

   A service function chain defines an ordered set of abstract service
   functions and ordering constraints that must be applied to packets
   and/or frames and/or flows selected as a result of classification
   [RFC7665].

   An example of an abstract service function is "a firewall".
   Typically, different tenant's traffic in cloud data center will
   traverse different services function chain containing Firewall, DPI
   or other VAS.

   Therefore, IPv6-based CON MUST have the capability to support SFC.





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4.1.7.  Performance Measurement

   Many OAM mechanisms are used to support network operation.
   Performance Measurement (PM) is one of the most important part of
   OAM.  With PM, the real-time QoS of the forwarding path, like delay,
   packet loss ratio and throughput, can be measured.

   PM can be implemented in one of three ways: active, passive, or
   hybrid [RFC7799], differing in whether OAM packets need to be
   proactively sent.

   On-path telemetry [I-D.song-opsawg-ifit-framework] is an hybrid mode
   OAM/PM mechanism, which provides better accuracy than active PM.
   Therefore, on-path Performance Measurement MUST be supported in
   IPv6-based CON.

4.1.8.  Reliability

   In Cloud-Network Interconnection scenarios, the enterprise traffic is
   forwarded over the WAN paths.  The traffic can be sensitive to delay
   or packet losing, so high reliability is required in these scenarios.
   Therefore, protection of node and links MUST be supported in
   IPv6-based CON.  Furthermore, redundancy transmission SHOULD be
   supported.

4.1.9.  Security

   As mentioned above, the enterprise traffic is forwarded over the WAN
   paths in IPv6-based CON.  The security of the traffic MUST be
   ensured.

   Also, in SD-WAN scenarios, customers are most concerned about
   security.

   Therefore, IPv6-based CON MUST support secure connection, and MUST
   provide security assurance for the traffic in transmission.

4.1.10.  Forwarding Efficiency

   Tenants/Customers rent the physical or logical WAN links/paths from
   network operators for building they cloud-network interconnection
   enterprise network, so the forwarding efficiency is important for the
   WAN path tenant.

   Path Maximum Transmission Unit indicates the maximum size of a packet
   that it can be forwarded along a path.  Setting an appropriate PMTU
   for packets can avoid fragmentation or dropping, so that the
   forwarding efficiency can be raised.



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   Also, the overhead of packets MUST be added very carefully since it
   affects the forwarding efficiency directly.  Especially, when many
   SIDs are inserted in an SRv6 packet, the overhead of the SID list is
   too large.  [I-D.srcompdt-spring-compression-requirement] describes
   the requirements of SRv6 compression.

   Therefore, the IPv6-based CON MUST support PMTU probing and
   configuration.  In addition, it MUST support SRv6 compression.

4.1.11.  Application-Aware Networking

   Network operators are typically unaware of which applications are
   traversing their networks, which is because the network layer is
   decoupled from application layer.  Adding application knowledge to
   the network layer enables finer granularity requirements of
   applications to be specified to the network operator.  As IPv6 is
   being widely deployed, the programmability provided by IPv6
   encapsulations can be augmented by conveying application information.

   In IPv6-based CON, many types of applications' traffic is exchanged
   between sites and clouds.  They have various requirements of QoS, and
   should be treated differently.  In order to provide finer granularity
   traffic engineering to reduce the cost of WAN services, application-
   aware networking SHOULD be supported in IPv6-based CON.

4.2.  Solutions

   This section describes the candidate solutions that meet the
   requirements in IPv6-based CON.

4.2.1.  VPN

   VPN is a basic and essential services for cloud-networks
   interconnections.

   SRv6 supports VPN by encoding the VPN information into the VPN SID
   [I-D.ietf-spring-srv6-network-programming].

   Based on IPv6, SRv6 VPN can be established across multiple domains.
   It avoids configuring VPN services at each boundary nodes at each
   domain like the way in IPv4/MPLS networks (Option A).  Deploying VPN
   based on SRv6 can shorten the duration significantly.

   Also, L2VPN and L3VPN can be supported uniformly based on EVPN
   control plane [I-D.ietf-bess-srv6-services].  Therefore, combining
   the SRv6 data plane and EVPN control plane, the VPN can be deployed
   in an easy and flexible way in IPv6-based CON.




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4.2.2.  Path Programming

   Based on SRv6, the traffic forwarding path can be programmed at the
   ingress of the SRv6 domain, so that the traffic from sites to clouds
   or inter-cloud can be forwarded through the specific underlay path.

   For instance, in SD-WAN scenarios, the POP GW can choose a specific
   underlay forwarding path in WAN by choosing a binding SID
   [I-D.dukes-spring-sr-for-sdwan].  If the CPE supports SRv6, a
   controller can convey the programmed path information to the CPE via
   BGP SRv6 policy [I-D.ietf-idr-segment-routing-te-policy] or PCEP SRv6
   policy [I-D.ietf-pce-segment-routing-policy-cp].

   If the WAN connection travels multiple domains, the WAN path can be
   connected by multiple tunnels, such as VXLAN, GRE tunnel.
   [I-D.dunbar-sr-sdwan-over-hybrid-networks] describes how to
   associated the tunnels.

   In order to shorten the delay, a CPE or PE can choose the nearest
   server in a specific cloud, and forward the packets through
   programmed paths.

4.2.3.  Service Function Chaining

   SFC is required in IPv6-based CON since different tenants subscribe
   different value-added services.

   [I-D.ietf-spring-sr-service-programming] defines the mechanism to
   support SFC in SRv6.  Each service function (SF) can be represented
   as an SRv6 SID if it supports SRv6.  If the SF is SRv6-unaware
   device, then proxy SID is used.  By programming service SIDs into the
   SRH, the SFC can be supported in SRv6.

   Thanks to IPv6 reachability, SRv6 supports to program the end-to-end
   forwarding path from the carrier network to the inside the cloud data
   center, even to multiple clouds.

   If NSH-based SFC has been deployed, a transition solution should be
   considered, and [I-D.ietf-spring-nsh-sr] describes a NSH and SR
   integration SFC solution.

4.2.4.  IPv6 based Network Slicing

   The tenant traffic MUST be isolated in WAN to avoid affecting by
   other internet traffic.

   A framework, Enhanced VPN (VPN+), to form an enhanced connectivity
   services between customer sites is defined as per



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   [I-D.ietf-teas-enhanced-vpn].  Typically, VPN+ will be used to form
   the underpinning of network slicing.  It also defines Virtual
   Transport Network (VTN).  A VTN is a virtual underlay network that
   connects customer edge points with the capability of providing the
   isolation and performance characteristics required by an enhanced VPN
   customer.  A VTN usually has a customized topology and a set of
   dedicated or shared network resources [I-D.ietf-teas-enhanced-vpn].

   A VTN-ID option in IPv6 HBH header is defined in
   [I-D.dong-6man-enhanced-vpn-vtn-id] to identify the Virtual Transport
   Network (VTN) the packet belongs to.  A VTN can be used as the
   underlay for one or a group of VPNs to provide enhanced VPN (VPN+)
   services.

   By using VTN-ID, an end-to-end IPv6 network slicing is identified in
   transport network.  Tenant traffic in WAN can be forwarded in the VTN
   with guaranteed resource.

4.2.5.  IPv6-based On-path Measurement

   The extension of supporting Alternate Marking Method [RFC8321] in
   IPv6 is defined in [I-D.ietf-6man-ipv6-alt-mark].  It describes how
   the Alternate Marking Method to be used as the hybrid performance
   measurement tool in an IPv6 domain by defining a new Extension Header
   Option.

   Alternate Marking Method is a hybrid on-path performance measurement
   method, and the metadata of each node can be collected by the
   collector to compute the performance of the path.

   IOAM is another on-path measurement method.
   [I-D.ietf-ippm-ioam-ipv6-options] defines a new IPv6 option, called
   IOAM option to support carrying IOAM metadata in the IPv6 data
   packet.  However, carrying all the metadata in the data packet will
   bring challenges for hardware processing.  For instance, long-length
   metadata may cause recircle in processing.  Therefore,
   [I-D.ietf-ippm-ioam-direct-export] defines a direct export option in
   IOAM, which enables the nodes to export the metadata to collector
   directly.  Furthermore,[I-D.song-opsawg-ifit-framework] outlines a
   high-level framework to provide an operational environment that
   utilizes existing and emerging on-path telemetry techniques to enable
   the collection and correlation of performance information from the
   network.








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4.2.6.  Reliability

4.2.6.1.  Local Protection

   Local protection mechanisms like Fast Reroute (FRR) provide 50 ms
   protection on nodes for traffic.

   Regarding link failures, TI-LFA
   [I-D.ietf-rtgwg-segment-routing-ti-lfa] provides a fast reroute
   mechanism by sending the traffic to an expected post-convergence
   paths from the point of local repair.

   Regarding the middle endpoint node failures,
   [I-D.hu-spring-segment-routing-proxy-forwarding] defines a mechanism
   for fast reroute protection against the failure of a SR-TE path.  It
   can provide fast reroute protection for an adjacency segment, a node
   segment and a binding segment of the path.  Also,
   [I-D.chen-rtgwg-srv6-midpoint-protection] defines midpoint
   protection, which enables the direct neighbor of the failed endpoint
   to perform the function of the endpoint, replace the IPv6 destination
   address to the next endpoint, and choose the next hop based on the
   new destination address.

   Regarding the egress node failures,
   [I-D.ietf-rtgwg-srv6-egress-protection] defines a local protection
   solution using the mirror SID.

4.2.6.2.  End-to-End Protection

   End-to-End Protection is also required in IPv6-based CON.  Normally,
   host-standby nodes are deployed for supporting traffic switching from
   the failed node to the alternative node.  In order to detect the
   failure, End-to-end BFD is required.  Once the BFD session is failed,
   the traffic can be steered into a disjoint forwarding path, and the
   traffic will be forwarded to the host-standby node.

4.2.6.3.  Redundancy Protection

   In order to avoid losing packets,
   [I-D.geng-spring-sr-redundancy-protection] defines a redundancy
   transmission solution.

   The document defines two types of segment including Redundancy
   Segment and Merging Segment to empower the Segment Routing with the
   capability of redundancy protection.






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4.2.7.  Security

   As per [I-D.li-spring-srv6-security-consideration], SRv6 inherits
   potential security vulnerabilities from Source Routing and IPv6, but
   it does not introduce new critical security threats.

   Regarding a limited domain, SPRING architecture [RFC8402] defines
   clear trusted domain boundaries so that source-routing information is
   only available within the trusted domain and never exposed to the
   outside of the domain.  It is expected that, by default, explicit
   routing is only used within the boundaries of the administered
   domain.  Therefore, the data plane does not expose any source-routing
   information when a packet leaves the trusted domain.  The traffic is
   filtered at the domain boundaries [RFC8402].

   However, it has been noted that the AH and ESP are not directly
   applicable in order to reduce the vulnerabilities of SRv6 due to the
   presence of mutable fields in the SRH
   [I-D.li-spring-srv6-security-consideration].  In order to resolve
   this problem, [RFC8754] defines a mechanism to carry HMAC TLV in the
   SRH to verify the integrity of packets including the SRH fields.

   Regarding end-to-end security protection across multiple domains, an
   end-to-end IPSec tunnel is suggested to be deployed.

   In typical SD-WAN scenarios, the IPSec tunnel should be used between
   the CPE and POP GW.

4.2.8.  IPv6 Forwarding Efficiency

4.2.8.1.  PMTU

   The host may discover the PMTU by Path MTU Discovery (PMTUD)
   [RFC8201] or other means.  But the ingress node still needs to
   examine the packet size to drop too large packets to avoid malicious
   packets or error packets attack.  Also, the packet size may exceed
   the PMTU because of the new encapsulation of SR-MPLS or SRv6 at the
   ingress.  In order to check whether the packet size exceeds the PMTU
   or not, the ingress node need to know the Path MTU associated to the
   forwarding path.

   However, the path maximum transmission unit (MTU) information for SR
   path is not available since the SR does not require signaling.
   [I-D.ietf-idr-bgp-ls-link-mtu] proposes a BGP-LS extensions to
   collect the link MTU of the links in the networks.
   [I-D.ietf-idr-sr-policy-path-mtu] and [I-D.li-pce-pcep-pmtu] defines
   extensions to distribute path MTU information within BGP and PCEP SR




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   policies, respectively.  In this way, the controller can compute the
   appropriate PMTU for an SR path.

4.2.8.2.  SRv6 Compression

   The overhead of SRv6 encapsulation brings challenges for hardware
   processing and transmission.
   [I-D.srcompdt-spring-compression-requirement] describes the
   requirements of SRv6 compression.

   G-SRv6 is proposed in [I-D.cl-spring-generalized-srv6-np], which
   supports to encode multiple types of SIDs in SRH.  This SRH is called
   Generalized SRH [I-D.lc-6man-generalized-srh] while the SID is called
   Generalized SID.

   G-SRv6 supports to encode the compressed SIDs in the SRH to reduce
   the size of SRv6 SID list in SRH
   [I-D.cl-spring-generalized-srv6-for-cmpr].  A COC (Continuation of
   Compression) flavor is defined to indicate the continuation of SRv6
   compressed SIDs in the SID list.

4.2.9.  Application-aware IPv6 Networking

   Application-aware Networking (APN) is proposed by
   [I-D.li-apn-framework], where application characteristic information
   such as application identification and its network performance
   requirements is carried in the packet encapsulation in order to
   facilitate service provisioning, perform application-level traffic
   steering and network resource adjustment.

   Application-aware IPv6 Networking (APN6) framework makes use of IPv6
   encapsulation in order to convey the application-aware information
   along with the data packet to the network so to facilitate the
   service deployment and SLA guarantee.
   [I-D.li-6man-app-aware-ipv6-network] defines the encodings of the
   application characteristic information, for the APN6 framework, that
   can be exchanged between an application and the network
   infrastructure through IPv6 extension headers.

5.  IANA Considerations

   TBD

6.  Security Considerations

   TBD





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7.  Contributors

   TBD



8.  Acknowledgements

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

9.2.  Informative References

   [I-D.ietf-rtgwg-net2cloud-problem-statement]
              Dunbar, L., Malis, A., Jacquenet, C., and M. Toy, "Dynamic
              Networks to Hybrid Cloud DCs Problem Statement", draft-
              ietf-rtgwg-net2cloud-problem-statement-11 (work in
              progress), July 2020.








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   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-28 (work in
              progress), December 2020.

   [I-D.ietf-bess-srv6-services]
              Dawra, G., Filsfils, C., Talaulikar, K., Raszuk, R.,
              Decraene, B., Zhuang, S., and J. Rabadan, "SRv6 BGP based
              Overlay services", draft-ietf-bess-srv6-services-05 (work
              in progress), November 2020.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <https://www.rfc-editor.org/info/rfc7665>.

   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <https://www.rfc-editor.org/info/rfc7799>.

   [I-D.dukes-spring-sr-for-sdwan]
              Dukes, D., Filsfils, C., Dawra, G., Xu, X., Voyer, D.,
              Camarillo, P., Clad, F., and S. Salsano, "SR For SDWAN:
              VPN with Underlay SLA", draft-dukes-spring-sr-for-sdwan-02
              (work in progress), June 2019.

   [I-D.dunbar-sr-sdwan-over-hybrid-networks]
              Dunbar, L. and M. Toy, "Segment routing for SDWAN paths
              over hybrid networks", draft-dunbar-sr-sdwan-over-hybrid-
              networks-06 (work in progress), November 2019.

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
              Rosen, E., Jain, D., and S. Lin, "Advertising Segment
              Routing Policies in BGP", draft-ietf-idr-segment-routing-
              te-policy-11 (work in progress), November 2020.

   [I-D.ietf-pce-segment-routing-policy-cp]
              Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
              Bidgoli, "PCEP extension to support Segment Routing Policy
              Candidate Paths", draft-ietf-pce-segment-routing-policy-
              cp-02 (work in progress), January 2021.








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   [I-D.ietf-spring-sr-service-programming]
              Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca,
              d., Li, C., Decraene, B., Ma, S., Yadlapalli, C.,
              Henderickx, W., and S. Salsano, "Service Programming with
              Segment Routing", draft-ietf-spring-sr-service-
              programming-03 (work in progress), September 2020.

   [I-D.ietf-spring-nsh-sr]
              Guichard, J. and J. Tantsura, "Integration of Network
              Service Header (NSH) and Segment Routing for Service
              Function Chaining (SFC)", draft-ietf-spring-nsh-sr-04
              (work in progress), December 2020.

   [I-D.ietf-teas-enhanced-vpn]
              Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A
              Framework for Enhanced Virtual Private Networks (VPN+)
              Service", draft-ietf-teas-enhanced-vpn-06 (work in
              progress), July 2020.

   [I-D.dong-6man-enhanced-vpn-vtn-id]
              Dong, J., Li, Z., Xie, C., and C. Ma, "Carrying Virtual
              Transport Network Identifier in IPv6 Extension Header",
              draft-dong-6man-enhanced-vpn-vtn-id-02 (work in progress),
              November 2020.

   [RFC8321]  Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli,
              L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
              "Alternate-Marking Method for Passive and Hybrid
              Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321,
              January 2018, <https://www.rfc-editor.org/info/rfc8321>.

   [I-D.ietf-6man-ipv6-alt-mark]
              Fioccola, G., Zhou, T., Cociglio, M., Qin, F., and R.
              Pang, "IPv6 Application of the Alternate Marking Method",
              draft-ietf-6man-ipv6-alt-mark-02 (work in progress),
              October 2020.

   [I-D.ietf-ippm-ioam-ipv6-options]
              Bhandari, S., Brockners, F., Pignataro, C., Gredler, H.,
              Leddy, J., Youell, S., Mizrahi, T., Kfir, A., Gafni, B.,
              Lapukhov, P., Spiegel, M., Krishnan, S., Asati, R., and M.
              Smith, "In-situ OAM IPv6 Options", draft-ietf-ippm-ioam-
              ipv6-options-04 (work in progress), November 2020.








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   [I-D.ietf-ippm-ioam-direct-export]
              Song, H., Gafni, B., Zhou, T., Li, Z., Brockners, F.,
              Bhandari, S., Sivakolundu, R., and T. Mizrahi, "In-situ
              OAM Direct Exporting", draft-ietf-ippm-ioam-direct-
              export-02 (work in progress), November 2020.

   [I-D.song-opsawg-ifit-framework]
              Song, H., Qin, F., Chen, H., Jin, J., and J. Shin, "In-
              situ Flow Information Telemetry", draft-song-opsawg-ifit-
              framework-13 (work in progress), October 2020.

   [I-D.ietf-rtgwg-segment-routing-ti-lfa]
              Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B.,
              and D. Voyer, "Topology Independent Fast Reroute using
              Segment Routing", draft-ietf-rtgwg-segment-routing-ti-
              lfa-05 (work in progress), November 2020.

   [I-D.hu-spring-segment-routing-proxy-forwarding]
              Hu, Z., Chen, H., Yao, J., Bowers, C., and Y. Zhu, "SR-TE
              Path Midpoint Protection", draft-hu-spring-segment-
              routing-proxy-forwarding-12 (work in progress), October
              2020.

   [I-D.chen-rtgwg-srv6-midpoint-protection]
              Chen, H., Hu, Z., Chen, H., and X. Geng, "SRv6 Midpoint
              Protection", draft-chen-rtgwg-srv6-midpoint-protection-03
              (work in progress), October 2020.

   [I-D.ietf-rtgwg-srv6-egress-protection]
              Hu, Z., Chen, H., Chen, H., Wu, P., Toy, M., Cao, C., He,
              T., Liu, L., and X. Liu, "SRv6 Path Egress Protection",
              draft-ietf-rtgwg-srv6-egress-protection-02 (work in
              progress), November 2020.

   [I-D.geng-spring-sr-redundancy-protection]
              Geng, X., Chen, M., and F. Yang, "Segment Routing for
              Redundancy Protection", draft-geng-spring-sr-redundancy-
              protection-00 (work in progress), November 2020.

   [I-D.li-spring-srv6-security-consideration]
              Li, C., Li, Z., Xie, C., Tian, H., and J. Mao, "Security
              Considerations for SRv6 Networks", draft-li-spring-srv6-
              security-consideration-05 (work in progress), October
              2020.







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   [RFC8201]  McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
              "Path MTU Discovery for IP version 6", STD 87, RFC 8201,
              DOI 10.17487/RFC8201, July 2017,
              <https://www.rfc-editor.org/info/rfc8201>.

   [I-D.ietf-idr-bgp-ls-link-mtu]
              Zhu, Y., Hu, Z., Peng, S., and R. Mwehair, "Signaling
              Maximum Transmission Unit (MTU) using BGP-LS", draft-ietf-
              idr-bgp-ls-link-mtu-00 (work in progress), November 2020.

   [I-D.ietf-idr-sr-policy-path-mtu]
              Li, C., Zhu, Y., Sawaf, A., and Z. Li, "Segment Routing
              Path MTU in BGP", draft-ietf-idr-sr-policy-path-mtu-02
              (work in progress), November 2020.

   [I-D.li-pce-pcep-pmtu]
              Peng, S., Li, C., Han, L., and L. Ndifor, "Support for
              Path MTU (PMTU) in the Path Computation Element (PCE)
              communication Protocol (PCEP).", draft-li-pce-pcep-pmtu-03
              (work in progress), October 2020.

   [I-D.srcompdt-spring-compression-requirement]
              Cheng, W., "Compressed SRv6 SID List Requirements", draft-
              srcompdt-spring-compression-requirement-03 (work in
              progress), January 2021.

   [I-D.cl-spring-generalized-srv6-np]
              Cheng, W., Li, Z., Li, C., Xie, C., Li, C., Tian, H., and
              F. Zhao, "Generalized SRv6 Network Programming", draft-cl-
              spring-generalized-srv6-np-02 (work in progress),
              September 2020.

   [I-D.lc-6man-generalized-srh]
              Li, Z., Li, C., Cheng, W., Xie, C., Cong, L., Tian, H.,
              and F. Zhao, "Generalized Segment Routing Header", draft-
              lc-6man-generalized-srh-01 (work in progress), August
              2020.

   [I-D.cl-spring-generalized-srv6-for-cmpr]
              Cheng, W., Li, Z., Li, C., Clad, F., Aihua, L., Xie, C.,
              Liu, Y., and S. Zadok, "Generalized SRv6 Network
              Programming for SRv6 Compression", draft-cl-spring-
              generalized-srv6-for-cmpr-02 (work in progress), November
              2020.







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   [I-D.li-apn-framework]
              Li, Z., Peng, S., Voyer, D., Li, C., Geng, L., Cao, C.,
              Ebisawa, K., Previdi, S., and J. Guichard, "Application-
              aware Networking (APN) Framework", draft-li-apn-
              framework-01 (work in progress), September 2020.

   [I-D.li-6man-app-aware-ipv6-network]
              Li, Z., Peng, S., Li, C., Xie, C., Voyer, D., Li, X., Liu,
              P., Liu, C., and K. Ebisawa, "Application-aware IPv6
              Networking (APN6) Encapsulation", draft-li-6man-app-aware-
              ipv6-network-02 (work in progress), July 2020.

Authors' Addresses

   Cheng Li (editor)
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: c.l@huawei.com


   Zhenbin Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: lizhenbin@huawei.com


   Hongjie Yang
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: hongjie.yang@huawei.com












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