Extension Header Use Cases

Introduction Extension headers have been specified since original 1995 IPv6 Specification and maintained in the more recently updated . In the nearly 30 years since extension headers were specified, there have been many documents which have specified how to limit, block and deprecate their use. What we haven't had is a document to show how extension headers are being deployed nor how related innovations are being proposed. This document outlines IPv6 extension header use cases including those intended to be deployed in limited domains and those deployed across the Internet. By understanding these various use cases we can better understand how best to improve upon, and perhaps limit, extension header deployment.

Glossary EH: IPv6 Extension Header Hop-by-Hop Optioners Header: Used to carry optional information intended for every node along the path. Routing Header: Used to list one or more nodes to be visited on the way to a packet's destination. Fragment Header: Used to send a packet larger than would fit in the path MTU to its destination. Encapsulating Security Payload: The Encapsulating Security Payload (ESP) extension header provides confidentiality, integrity, and authentication for IPv6 packets. Authentication Header: The IPv6 Authentication Header (AH) extension provides data integrity, authentication, and anti-replay protection for IPv6 packets. Destination Options Header: Used to carry optional information for destination nodes. Mobility Header: The Mobility Header enables mobility support for network nodes in IPv6 networks. Host Identity Protocol: The Host Identity Protocol (HIP) provides a cryptographic identity-based solution for secure communication and mobility management in IPv6 networks. Shim6 Protocol: The Shim6 IPv6 extension header enables multihoming by providing source and destination address selection for efficient routing. Single Administrative Domain: The EH is limited to one administrative domain. Limited Domain: The EH is limited to a group of administrative domains. Unlimited Domain: The EH is not limited to any group of domains.

IPv6 Extension Header Types

Existing IPv6 Extension Header Use Cases In this section we list and describe, several extension header use cases. We will specify if the use case is intended for a limited domain and the status of its deployment. We further categorize the EH into a category. The categories are the following: Another crucial aspect in characterizing extension header usage is to determine whether the EH is intended for a single administrative domain, a limited domain, or an unlimited domain. Furthermore, it is important to consider the potential consequences if the EH is modified, which could be a result of transmission errors or intentional alterations. It is also necessary to assess whether the EH contains private data that, if exposed, could lead to a data leak.
This evaluation may prompt a deeper discussion on the additional safeguards that should be implemented, such as incorporating a checksum, a signature, or encryption mechanisms for the EH.

Detailed Description of Categories

Quality of Service (QoS) Extension Headers: These extension headers can be used to prioritize and manage traffic based on different quality of service parameters such as latency, bandwidth, packet loss, or reliability. They allow for fine-grained control over QoS policies within an IPv6 network.
Network Security Extension Headers: These extension headers provide enhanced security features for IPv6, such as authentication, integrity checks, encryption, or firewall rules. They can be used to enforce network security policies at the IP layer, complementing higher-layer security protocols.
Network Management Extension Headers: These extension headers facilitate network management operations by including information related to network monitoring, performance measurement, or configuration management. They enable administrators to efficiently manage and troubleshoot IPv6 networks.
Application-Specific Extension Headers: These extension headers cater to specific application requirements by carrying application-specific metadata or instructions. They can be used to enable application-specific optimizations or provide additional context to the network for better application performance.
Internet of Things (IoT) Extension Headers: These extension headers include information about device capabilities, power management, sensor data, or IoT-specific protocols to enable efficient communication and management of IoT devices over IPv6.
Content Delivery Networks (CDN) Extension Headers: These extension headers optimize content delivery over IPv6 by including information related to content caching, replication, or load balancing within a content delivery network. They allow for efficient content distribution and improved performance for CDN-enabled services.
Routing Extension Headers: These extension headers supplement existing information about routing policies, traffic engineering, or multicast routing to enhance the routing capabilities of IPv6.

Existing Destination and Hop-by-Hop Options The following is the list of Destination Options and Hop-by-Hop Options which have an option number at IANA. Note, we will describe use cases, if any, for options which do not have an option number at IANA. [ToBeDone: Separate these into Destination Options and Hop-by-hop options]

Existing Routing Types The following is the list of Routing Types which are defined at IANA. Note, we will describe use cases, if any, for options which do not have an option number at IANA. Segment Routing Header TLVs

Quality of Service (QoS) Extension Headers

Existing QoS Extension Headers

Potential QoS Extension Headers

Network Management Extension Headers

Existing Network Management Extension Headers

RFC8250: Performance and Diagnostic Metrics (PDM) RFC 8250 specifies the Performance and Diagnostic Metrics (PDM) Destination Options header, which is used to measure the performance of IPv6 networks. The PDM header contains sequence numbers and timing information that can be used to calculate metrics such as round-trip delay and server delay. The PDM header is embedded in each packet, and the information it contains is combined with the 5-tuple (source IP address, source port, destination IP address, destination port, and upper-layer protocol) to calculate the metrics. The PDM header also includes fields for storing time scaling factors, which can be used to adjust the measurements for different network conditions. The PDM header can be used to assess performance problems in real time or after the fact. The measurements can be used to troubleshoot network problems, identify bottlenecks, and optimize network performance.

Potential Network Management Extension Headers

Network Security Extension Headers

Existing Network Security Extension Headers

Potential Network Security Extension Headers

Application Specific Extension Headers

Existing Application Specific Extension Headers

Potential Application Specific Extension Headers

Internet of Things (IoT) Extension Headers

Existing IoT Extension Headers

Potential IoT Extension Headers

Content Delivery Networks (CDN) Extension Headers

Existing CDN Extension Headers

Potential CDN Extension Headers

Routing Extension Headers

Existing Routing Extension Headers

Segment Routing Header (SRH) Segment Routing (SR) can be applied to the IPv6 data plane using a routing header called the Segment Routing Header (SRH). specifies the encoding of IPv6 segments in an SRH. SRv6 uses this IPv6 Routing Extension Header to forward IPv6 packets using the source routing model. It implements hop-by-hop forwarding by adding a Segment Routing header (SRH) into IPv6 packets, encapsulating an explicit IPv6 address stack into the SRH, and continuously updating IPv6 destination addresses while offsetting the address stack on transit nodes. According to , there have been over 10 announced deployments of an SRH based data plane and over 20 additional deployments without public announcements.

Mobility Header specifies Mobile IPv6, a protocol that allows nodes to remain reachable while moving around in the IPv6 Internet.The Mobility Header is an extension header used by mobile nodes, correspondent nodes, and home agents in all messaging related to the creation and management of mobile bindings. The Mobility Header is identified by a Next Header value of 135.

MLD Messages Multicast Listener Discovery (MLD) is used today by IPv6 routers for discovering multicast listeners on a directly attached link, much like Internet Group Management Protocol (IGMP) is used in IPv4. MLD uses ICMPv6 (IP Protocol 58) message types, rather than IGMP (IP Protocol 2) message types. MLD messages are identified in IPv6 packets by a preceding Next Header value of 58. MLD messages are sent with an IPv6 Router Alert option in a Hop-by-Hop Options header as defined in RFC 2710.

Potential Routing Extension Headers

Integrated Multicast Bitstring There's a potential deployment of using a bitstring (such as used in BIER) as part of the IPv6 data plane using an EH. >| | | |<----------(L3 BIER(P2MP) tunnel)---------->| | | | SEP SEP SEP SEP | | +******************+ +****+ | | / \ / \ | +------+ +-------+ +-----+ +------+ | BFIR |-------|Non-BFR|-------| BFR |--------| BFER | +------+ +-------+ +-----+ +------+ ------- L2 link ******* IPv6(P2P) segment (SEP = Segment EndPoint) <-----> BIER(P2MP) tunnel ]]> In this deployment, BIER works as part of the IPv6 data plane. The BFIR and BFERs work as IPv6 (P2MP) tunnel endpoints, and BFRs work as IPv6 segment endpoints. The BIER header is processed on each segment endpoint and there is no decapsulation, or re-encapsulation, on the segment endpoints. This deployment typically needs an IPv6 extension header to carry the BIER header and processing of the BIER header (e.g., the bitstring) will be implemented as part of the IPv6 extension header processing. The IPv6 source address is the BIER packet source-origin identifier, and is unchanged through the BIER domain from BFIR to BFERs.

Security Considerations None.

Privacy Considerations None.

IANA Considerations None.

Contributors Thanks to Dr. Tommaso Pecorella and Dhruv Dhody for their comments.

Change Log Note to RFC Editor: if this document does not obsolete an existing RFC, please remove this appendix before publication as an RFC

Open Issues Note to RFC Editor: please remove this appendix before publication as an RFC