]> Univ. of Rome Tor Vergata / CNIT

stefano.salsano@uniroma2.it

Consultant

helbakoury@gmail.com

Telefonica, I+D

diego.r.lopez@telefonica.com

AREA WG Working Group IPv6 Extension Headers Extensible In-band Processing (EIP) extends the functionality of the IPv6 protocol considering the needs of future Internet services / 6G networks. This document discusses the architecture and framework of EIP. Two separate documents respectively analyze a number of use cases for EIP and provide the protocol specifications of EIP. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the EIP SIG mailing list (), which is archived at . Source for this draft and an issue tracker can be found at .

Introduction Networking architectures need to evolve to support the needs of future Internet services and 6G networks. The networking research and standardization communities have considered different approaches for this evolution, that can be broadly classified in 3 different categories:

1. Clean slate and "revolutionary" solutions. Throw away the legacy IP networking layer.
2. Solutions above the layer 3. Do not touch the legacy networking layer (IP).
3. Evolutionary solutions. Improve the IP layer (and try to preserve backward compatibility).

The proposed EIP (Extensible In-band Processing) solution belongs to the third category, it extends the current IPv6 architecture without requiring a clean-slate revolution. The use cases for EIP are discussed in . The specification of the EIP header format is provided in .

Basic principles for EIP An ongoing trend is extending the functionality of the IPv6 networking layer, going beyond the plain packet forwarding. An example of this trend is the rise of the SRv6 "network programming" model. With the SRv6 network programming model, the routers can implement "complex" functionalities and they can be controlled by a "network program" that is embedded in IPv6 packet headers. Another example is the INT (IN band Telemetry) solution for monitoring. These (and other) examples are further discussed in . The EIP solution is aligned with this trend, which will ensure a future proof evolution of networking architectures. EIP supports a feature-rich and extensible IPv6 networking layer, in which complex dataplane functions can be executed by end-hosts, routers, virtual functions, servers in datacenters so that services can be implemented in the smartest and more efficient way. The EIP solution foresees the introduction of an EIP header in the IPv6 packet header. The proposed EIP header is extensible and it is meant to support a number of different use cases. In general, both end-hosts and transit routers can read and write the content of this header. Depending of the specific use-case, only specific nodes will be capable and interested in reading or writing the EIP header. The use of the EIP header can be confined to a single domain or to a set of cooperating domains, so there is no need of a global, Internet-wide support of the new header for its introduction. Moreover, there can be usage scenarios in which legacy nodes can simply ignore the EIP header and provide transit to packets containing the EIP header. An important usage scenario considers the transport of user packets over a provider network. In this scenario, we consider the network portion from the provider ingress edge node to the provider egress edge node. The ingress edge node can encapsulate the user packet coming from an access network into an outer packet. The outer packet travels in the provider network until the egress edge node, which will decapsulate the inner packet and deliver it to the destination access network or to another transit network, depending on the specific topology and service. Assuming that the IPv6/SRv6 dataplane is used in the provider network, the ingress edge node will be the source of an outer IPv6 packet in which it is possible to add the EIP header. The outer IPv6 packet (containing the EIP header) will be processed inside the "limited domain" (see ) of the provider network, so that the operator can make sure that all the transit routers either are EIP aware or at least they can forward packets containing the EIP header. In this usage scenario, the EIP framework operates "edge-to-edge" and the end-user packets are "tunneled" over the EIP domain. The architectural framework for EIP is depicted in . We refer to nodes that are not EIP capable as legacy nodes. An EIP domain is made up by EIP aware routers (EIP R) and can also include legacy routers (LEG R). At the border of the EIP domain, EIP edge nodes (EIP ER) are used to interact with legacy End Hosts / Servers (LEG H) and with other domains. It is also possible that an End Host / Server is EIP aware (EIP H), in this case the EIP framework could operate "edge-to-end" or "end-to-end".

EIP framwork

As shown in , an EIP domain can communicate with other domains, which can be legacy domains or EIP capable domains.

Benefits of a common EIP header for multiple use cases. The EIP header will carry different EIP Information Elements that are defined to support the different use cases. There are reasons why it is beneficial to define a common EIP header that supports multiple use cases.

1. The number of available Option Types in HBH header is limited, likewise the number of available TLVs in the Segment Routing Header (SRH) is limited. Defining multiple Option Types or SRH TLVs for multiple use case is not scalable and puts pressure on the allocation of such codepoints. This aspect is further discussed in .
2. The definition and standardization of specific EIP Information Elements for the different use cases will be simplified, compared to the need of requiring the definition of a new Option Type or SRH TLVs.
3. Different use cases may share a subset of common EIP Information Elements.
4. Efficient mechanism for the processing of the EIP header (both in software and in hardware) can be defined when the different EIP Information Elements are carried inside the same EIP header.

Review of standardized and proposed evolutions of IPv6 In the last few years, we have witnessed important innovations in IPv6 networking, centered around the emergence of Segment Routing for IPv6 (SRv6) and of the SRv6 "Network Programming model" . With SRv6 it is possible to insert a Network program, i.e. a sequence of instructions (called segments), in a header of the IPv6 protocol, called Segment Routing Header (SRH). Another recent activity that proposed to extend the networking layer to support more complex functions, concerns the network monitoring. The concept of INT "In-band Network Telemetry" has been proposed since 2015 in the context of the definition of use cases for P4 based data plane programmability. The latest version of INT specifications dates November 2020 . specifies the format of headers that carry monitoring instructions and monitoring information along with data plane packets. The specific location for INT Headers is intentionally not specified: an INT Header can be inserted as an option or payload of any encapsulation type. The In-band Telemetry concept has been adopted by the IPPM IETF Working Group, renaming it "In-situ Operations, Administration, and Maintenance" (IOAM). The internet draft is about to become an IETF RFC. Note that IOAM is focused on "limited domains" as defined in . The in-situ OAM data fields can be encapsulated in a variety of protocols, including IPv6. The specification details for carrying IOAM data inside IPv6 headers are provided in draft , which is also close to becoming an RFC. In particular, IOAM data fields can be encapsulated in IPv6 using either Hop-by-Hop Options header or Destination options header. Another example of extensions to IPv6 for network monitoring is specified in , which defines an IPv6 Destination Options header called Performance and Diagnostic Metrics (PDM). The PDM option header provides sequence numbers and timing information as a basis for measurements. The "Alternate Marking Method" is a recently proposed performance measurement approach described in . The draft (also close to becoming an RFC) defines a new Hop-by-Hop Option to support this approach. "Path Tracing" proposes an efficient solution for recording the route taken by a packet (including timestamps and load information taken at each hop along the route). This solution needs a new Hop-by-Hop Option to be defined. analyses the evolution of transport protocols. It recommends that explicit signals should be used when the endpoints desire that network elements along the path become aware of events related to trasport protocol. Among the solutions, considers the use of explicit signals at the network layer, and in particular it mentions that IPv6 hop-by-hop headers might suit this purpose. The Internet Draft specifies a new IPv6 Hop-by-Hop option that is used to record the minimum Path MTU between a source and a destination. This draft is close to become an RFC.

Consideration on Hop-by-hop Options allocation We have listed several proposals or already standardized solutions that use the IPv6 Hop-by-Hop Options. These Options are represented with a 8 bits code. The first two bits represent the action to be taken if the Options is unknown to a node that receives it, the third bit is used to specify if the content of the Options can be changed in flight. In particular the Option Types that start with 001 should be ignored if unknown and can be changed in flight, which is the most common combination. The current IANA allocation for Option Types starting with 001 is (see https://www.iana.org/assignments/ipv6-parameters/ipv6-parameters.xhtml) We observe that there is a potential scarcity of the code points, as there are many scenarios that could require the definition of a new Hop-by-hop option. We also observe that having only 1 code point allocated for experiments is a very restrictive limitation.

Conventions and Definitions 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 when, and only when, they appear in all capitals, as shown here.

Security Considerations TODO Security

IANA Considerations The definition of the EIP header as an Option for IPv6 Hop-by-hop Extension header requires the allocation of a codepoint from the "Destination Options and Hop-by-Hop Options" registry in the "Internet Protocol Version 6 (IPv6) Parameters" (https://www.iana.org/assignments/ipv6-parameters/ipv6-parameters.xhtm). The definition of the EIP header as a TLV in the Segment Routing Header requires the allocation of a codepoint from the "Segment Routing Header TLVs" registry in the "Internet Protocol Version 6 (IPv6) Parameters" (https://www.iana.org/assignments/ipv6-parameters/ipv6-parameters.xhtm). The definition of EIP Information Elements in the EIP header will require the definition of a IANA registry.

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References Segment Routing can be applied to the IPv6 data plane using a new type of Routing Extension Header called the Segment Routing Header (SRH). This document describes the SRH and how it is used by nodes that are Segment Routing (SR) capable. The Segment Routing over IPv6 (SRv6) Network Programming framework enables a network operator or an application to specify a packet processing program by encoding a sequence of instructions in the IPv6 packet header. Each instruction is implemented on one or several nodes in the network and identified by an SRv6 Segment Identifier in the packet. This document defines the SRv6 Network Programming concept and specifies the base set of SRv6 behaviors that enables the creation of interoperable overlays with underlay optimization. There is a noticeable trend towards network behaviors and semantics that are specific to a particular set of requirements applied within a limited region of the Internet. Policies, default parameters, the options supported, the style of network management, and security requirements may vary between such limited regions. This document reviews examples of such limited domains (also known as controlled environments), notes emerging solutions, and includes a related taxonomy. It then briefly discusses the standardization of protocols for limited domains. Finally, it shows the need for a precise definition of "limited domain membership" and for mechanisms to allow nodes to join a domain securely and to find other members, including boundary nodes. This document is the product of the research of the authors. It has been produced through discussions and consultation within the IETF but is not the product of IETF consensus. To assess performance problems, this document describes optional headers embedded in each packet that provide sequence numbers and timing information as a basis for measurements. Such measurements may be interpreted in real time or after the fact. This document specifies the Performance and Diagnostic Metrics (PDM) Destination Options header. The field limits, calculations, and usage in measurement of PDM are included in this document. This document describes a method to perform packet loss, delay, and jitter measurements on live traffic. This method is based on an Alternate-Marking (coloring) technique. A report is provided in order to explain an example and show the method applicability. This technology can be applied in various situations, as detailed in this document, and could be considered Passive or Hybrid depending on the application. This document discusses the nature of signals seen by on-path elements examining transport protocols, contrasting implicit and explicit signals. For example, TCP's state machine uses a series of well-known messages that are exchanged in the clear. Because these are visible to network elements on the path between the two nodes setting up the transport connection, they are often used as signals by those network elements. In transports that do not exchange these messages in the clear, on-path network elements lack those signals. Often, the removal of those signals is intended by those moving the messages to confidential channels. Where the endpoints desire that network elements along the path receive these signals, this document recommends explicit signals be used. Cisco Systems, Inc. Thoughtspot Huawei In situ Operations, Administration, and Maintenance (IOAM) collects operational and telemetry information in the packet while the packet traverses a path between two points in the network. This document discusses the data fields and associated data types for IOAM. IOAM-Data-Fields can be encapsulated into a variety of protocols, such as Network Service Header (NSH), Segment Routing, Generic Network Virtualization Encapsulation (Geneve), or IPv6. IOAM can be used to complement OAM mechanisms based on, e.g., ICMP or other types of probe packets. Thoughtspot Cisco Systems, Inc. In-situ Operations, Administration, and Maintenance (IOAM) records operational and telemetry information in the packet while the packet traverses a path between two points in the network. This document outlines how IOAM data fields are encapsulated in IPv6. Huawei Huawei Telecom Italia China Mobile China Unicom This document describes how the Alternate Marking Method can be used as a passive performance measurement tool in an IPv6 domain. It defines a new Extension Header Option to encode Alternate Marking information in both the Hop-by-Hop Options Header and Destination Options Header. Cisco Systems, Inc. Cisco Systems, Inc. Cisco Systems, Inc. Broadcom Swisscom Alibaba, Inc SoftBank Goldman Sachs Path Tracing provides a record of the packet path as a sequence of interface ids. In addition, it provides a record of end-to-end delay, per-hop delay, and load on each egress interface along the packet delivery path. Path Tracing allows to trace 14 hops with only a 40-bytes IPv6 Hop- by-Hop extension header. Path Tracing supports fine grained timestamp. It has been designed for linerate hardware implementation in the base pipeline. Check Point Software University of Aberdeen This document specifies a new IPv6 Hop-by-Hop option that is used to record the minimum Path MTU along the forward path between a source host to a destination host. The recorded value can then be communicated back to the source using the return Path MTU field in the option. Univ. of Rome Tor Vergata / CNIT Consultant Univ. of Rome Tor Vergata / CNIT Consultant n.d.

Acknowledgments TODO acknowledge.