Juniper Networks

2251 Corporate Park Drive Herndon 20171 VA United States of America rbonica@juniper.net

NTT Communications Corporation

3-4-1 Shibaura, Minato-ku Tokyo 108-8118 Japan y.kamite@ntt.com

Alston Networks

Nairobi Kenya aa@alstonnetworks.net

Liquid Telecom

Johannesburg South Africa daniam.henriques@liquidtelecom.com

Verizon

Richardson TX United States of America luay.jalil@one.verizon.com

INT 6man IPv6 Routing header This document describes an experiment in which two new IPv6 Routing headers are implemented and deployed. Collectively, they are called the Compact Routing Header (CRH). Individually, they are called CRH-16 and CRH-32. One purpose of this experiment is to demonstrate that the CRH can be implemented and deployed in a production network. Another purpose is to demonstrate that the security considerations described in this document can be addressed with Access Control Lists (ACLs). Finally, this document encourages replication of the experiment.

Status of This Memo This document is not an Internet Standards Track specification; it is published for examination, experimental implementation, and evaluation. This document defines an Experimental Protocol for the Internet community. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are candidates for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

Copyright Notice Copyright (c) 2024 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 () 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.

Table of Contents

• .  Introduction
• .  Requirements Language
• .  The Compact Routing Header (CRH)
• .  The CRH Forwarding Information Base (CRH-FIB)
• .  Processing Rules
  • .  Computing Minimum CRH Length
• .  Mutability
• .  Applications and CRH SIDs
• .  Operational Considerations
• .  Textual Representations
• . Security Considerations
• . Experimental Results
• . IANA Considerations
• . References
  • .  Normative References
  • .  Informative References
• .  CRH Processing Examples
  • .  The CRH SID list contains one entry for each segment in the path.
  • .  The CRH SID list omits the first entry in the path.
• Acknowledgements
• Contributors
• Authors' Addresses

Introduction IPv6 source nodes use Routing headers to specify the path that a packet takes to its destination(s). The IETF has defined several Routing Types; see . This document defines two new Routing Types. Collectively, they are called the Compact Routing Header (CRH). Individually, they are called CRH-16 and CRH-32. The CRH allows IPv6 source nodes to specify the path that a packet takes to its destination. The CRH can be encoded in relatively few bytes. The following are reasons for encoding the CRH in as few bytes as possible:

• Many forwarders based on Application-Specific Integrated Circuits (ASICs) copy headers from buffer memory to on-chip memory. As header sizes increase, so does the cost of this copy.
• Because Path MTU Discovery (PMTUD) is not entirely reliable, many IPv6 hosts refrain from sending packets larger than the IPv6 minimum link MTU (i.e., 1280 bytes). When packets are small, the overhead imposed by large Routing headers is excessive.

This document describes an experiment with the following purposes:

• To demonstrate that the CRH can be implemented and deployed
• To demonstrate that the security considerations described in this document can be addressed with ACLs
• To encourage replication of the experiment

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

The Compact Routing Header (CRH) Both CRH versions (i.e., CRH-16 and CRH-32) contain the following fields:

• Next Header, as defined in
• Hdr Ext Len, as defined in
• Routing Type, as defined in (CRH-16 value is 5, and CRH-32 value is 6.)
• Segments Left, as defined in
• type-specific data, as described in

In the CRH, the type-specific data field contains a list of CRH Segment Identifiers (CRH SIDs). Each CRH SID identifies an entry in the CRH Forwarding Information Base (CRH-FIB) (). Each CRH-FIB entry identifies an interface on the path that the packet takes to its destination. CRH SIDs are listed in reverse order. So, the first CRH SID in the list represents the final interface in the path. Because CRH SIDs are listed in reverse order, the Segments Left field can be used as an index into the CRH SID list. In this document, the "current CRH SID" is the CRH SID list entry referenced by the Segments Left field. The first CRH SID in the path is omitted from the list unless there is some reason to preserve it. See for an example. In the CRH-16 (), each CRH SID is encoded in 16 bits. In the CRH-32 (), each CRH SID is encoded in 32 bits. In all cases, the CRH MUST end on a 64-bit boundary. So, the type-specific data field MUST be padded with zeros if the CRH would otherwise not end on a 64-bit boundary.

CRH-16 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | Routing Type | Segments Left | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID[0] | SID[1] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | ......... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

CRH-32 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | Routing Type | Segments Left | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + SID[0] + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + SID[1] + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ......... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

The CRH Forwarding Information Base (CRH-FIB) Each CRH SID identifies a CRH-FIB entry. Each CRH-FIB entry contains:

• An IPv6 address
• A topological function
• Arguments for the topological function (optional)

The IPv6 address can be a Global Unicast Address (GUA), a Link-Local Unicast (LLU) address, or a Unique Local Address (ULA). When the IPv6 address is the final address in a path, it can also be a multicast address. The topological function specifies how the processing node forwards the packet to the interface identified by the IPv6 address. The following are examples:

• Forward the packet through the least-cost path to the interface identified by the IPv6 address (i.e., loose source routing).
• Forward the packet through a specified interface to the interface identified by the IPv6 address (i.e., strict source routing).

Some topological functions require parameters. For example, a topological function might require a parameter that identifies the interface through which the packet is forwarded. The CRH-FIB can be populated by:

• An operator, using a Command Line Interface (CLI)
• A controller, using the Path Computation Element Communication Protocol (PCEP) or the Network Configuration Protocol (NETCONF)
• A distributed routing protocol, such as those defined in , , and

The above-mentioned mechanisms are not defined here and are beyond the scope of this document.

Processing Rules The following rules describe CRH processing:

• If Hdr Ext Len indicates that the CRH is larger than the implementation can process, discard the packet and send an ICMPv6 Parameter Problem, Code 0, message to the Source Address, pointing to the Hdr Ext Len field.
• Compute L, the minimum CRH length ( ).
• If L is greater than Hdr Ext Len, discard the packet and send an ICMPv6 Parameter Problem, Code 6, message to the Source Address, pointing to the Segments Left field.
• Decrement Segments Left.
• Search for the current CRH SID in the CRH-FIB. In this document, the "current CRH SID" is the CRH SID list entry referenced by the Segments Left field.
• If the search does not return a CRH-FIB entry, discard the packet and send an ICMPv6 Parameter Problem, Code 0, message to the Source Address, pointing to the current SID.
• If Segments Left is greater than 0 and the CRH-FIB entry contains a multicast address, discard the packet and send an ICMPv6 Parameter Problem, Code 0, message to the Source Address, pointing to the current SID. (This prevents packet storms.)
• Copy the IPv6 address from the CRH-FIB entry to the Destination Address field in the IPv6 header.
• Submit the packet, its topological function, and its parameters to the IPv6 module.

Computing Minimum CRH Length The algorithm described in this section accepts the following CRH fields as its input parameters:

• Routing Type (i.e., CRH-16 or CRH-32)
• Segments Left

It yields L, the minimum CRH length. The minimum CRH length is measured in 8-octet units, not including the first 8 octets. switch(Routing Type) { case CRH-16: if (Segments Left <= 2) return(0) sidsBeyondFirstWord = Segments Left - 2; sidPerWord = 4; case CRH-32: if (Segments Left <= 1) return(0) sidsBeyondFirstWord = Segments Left - 1; sidsPerWord = 2; case default: return(0xFF); } words = sidsBeyondFirstWord div sidsPerWord; if (sidsBeyondFirstWord mod sidsPerWord) words++; return(words)

Mutability In the CRH, the Segments Left field is mutable. All remaining fields are immutable.

Applications and CRH SIDs A CRH contains one or more CRH SIDs. Each CRH SID is processed by exactly one CRH-configured router whose one address matches the packet Destination Address. Therefore, a CRH SID is not required to have domain-wide significance. Applications can allocate CRH SIDs so that they have either domain-wide or node-local significance.

Operational Considerations PING and Traceroute both operate correctly in the presence of the CRH. TCPDUMP and Wireshark have been extended to support the CRH. PING and Traceroute report 16-bit CRH SIDs for CRH-16 and 32-bit CRH SIDs for CRH-32. It is recommended that the experimental versions of PING use the textual representations described in .

Textual Representations A 16-bit CRH SID can be represented by four lowercase hexadecimal digits. Leading zeros SHOULD be omitted. However, the all-zeros CRH SID MUST be represented by a single 0. The following are examples:

• beef
• eef
• 0

A 16-bit CRH SID also can be represented in dotted-decimal notation. The following are examples:

• 192.0
• 192.51

A 32-bit CRH SID can be represented by four lowercase hexadecimal digits, a colon (:), and another four lowercase hexadecimal digits. Leading zeros MUST be omitted. The following are examples:

• dead:beef
• ead:eef
• :beef
• beef:
• :

A 32-bit CRH SID can also be represented in dotted-decimal notation. The following are examples:

• 192.0.2.1
• 192.0.2.2
• 192.0.2.3

Security Considerations In this document, one node trusts another only if both nodes are operated by the same party. A node determines whether it trusts another node by examining its IP address. In many networks, operators number their nodes using a small number of prefixes. This facilitates identification of trusted nodes. A node can encounter security vulnerabilities when it processes a Routing header that originated on an untrusted node . Therefore, nodes MUST deploy ACLs that discard packets containing the CRH when both of the following conditions are true:

• The Source Address does not identify an interface on a trusted node.
• The Destination Address identifies an interface on the local node.

The above-mentioned ACLs do not protect the node from attack packets that contain a forged (i.e., spoofed) Source Address. In order to mitigate this risk, nodes MAY also discard packets containing the CRH when all of the following conditions are true:

• The Source Address identifies an interface on a trusted node.
• The Destination Address identifies an interface on the local node.
• The packet does not pass an Enhanced Feasible-Path Unicast Reverse Path Forwarding (EFP-uRPF) check.

The EFP-uRPF check eliminates some, but not all, packets with forged Source Addresses. Therefore, a network operator that deploys CRH MUST implement ACLs on each of its edge nodes. The ACL discards packets whose Source Address identifies an interface on a trusted node. The CRH is compatible with end-to-end IPv6 Authentication Header (AH) processing. This is because the source node calculates the Integrity Check Value (ICV) over the packet as it arrives at the destination node.

Experimental Results Parties participating in this experiment should publish experimental results within one year of the publication of this document. Experimental results should address the following:

• Effort required to deploy
  • Was deployment incremental or network-wide?
  • Was there a need to synchronize configurations at each node, or could nodes be configured independently?
  • Did the deployment require a hardware upgrade?
  • Did the CRH SIDs have domain-wide or node-local significance?
• Effort required to secure
• Performance impact
• Effectiveness of risk mitigation with ACLs
• Cost of risk mitigation with ACLs
• Mechanism used to populate the CRH-FIB
• Scale of deployment
• Interoperability
  • Did you deploy two interoperable implementations?
  • Did you experience interoperability problems?
  • Did implementations generally implement the same topological functions with identical arguments?
  • Were topological function semantics identical on each implementation?
• Effectiveness and sufficiency of Operations, Administration, and Maintenance (OAM) mechanisms
  • Did PING work?
  • Did Traceroute work?
  • Did Wireshark work?
  • Did TCPDUMP work?

IANA Considerations IANA has registered the following in the "Routing Types" subregistry within the "Internet Protocol Version 6 (IPv6) Parameters" registry:

Value	Description	Reference
5	CRH-16	RFC 9631
6	CRH-32	RFC 9631

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. This document describes an updated version of the IP Authentication Header (AH), which is designed to provide authentication services in IPv4 and IPv6. This document obsoletes RFC 2402 (November 1998). [STANDARDS-TRACK] This document describes the format of a set of control messages used in ICMPv6 (Internet Control Message Protocol). ICMPv6 is the Internet Control Message Protocol for Internet Protocol version 6 (IPv6). [STANDARDS-TRACK] The functionality provided by IPv6's Type 0 Routing Header can be exploited in order to achieve traffic amplification over a remote path for the purposes of generating denial-of-service traffic. This document updates the IPv6 specification to deprecate the use of IPv6 Type 0 Routing Headers, in light of this security concern. [STANDARDS-TRACK] 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. This document specifies version 6 of the Internet Protocol (IPv6). It obsoletes RFC 2460. Informative References IANA ISO/IEC Second Edition This memo is an introductory guide to many of the most commonly- available TCP/IP and Internet tools and utilities. It also describes discussion lists accessible from the Internet, ways to obtain Internet and TCP/IP documents, and some resources that help users weave their way through the Internet. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. This document discusses the Border Gateway Protocol (BGP), which is an inter-Autonomous System routing protocol. The primary function of a BGP speaking system is to exchange network reachability information with other BGP systems. This network reachability information includes information on the list of Autonomous Systems (ASes) that reachability information traverses. This information is sufficient for constructing a graph of AS connectivity for this reachability from which routing loops may be pruned, and, at the AS level, some policy decisions may be enforced. BGP-4 provides a set of mechanisms for supporting Classless Inter-Domain Routing (CIDR). These mechanisms include support for advertising a set of destinations as an IP prefix, and eliminating the concept of network "class" within BGP. BGP-4 also introduces mechanisms that allow aggregation of routes, including aggregation of AS paths. This document obsoletes RFC 1771. [STANDARDS-TRACK] This document describes the modifications to OSPF to support version 6 of the Internet Protocol (IPv6). The fundamental mechanisms of OSPF (flooding, Designated Router (DR) election, area support, Short Path First (SPF) calculations, etc.) remain unchanged. However, some changes have been necessary, either due to changes in protocol semantics between IPv4 and IPv6, or simply to handle the increased address size of IPv6. These modifications will necessitate incrementing the protocol version from version 2 to version 3. OSPF for IPv6 is also referred to as OSPF version 3 (OSPFv3). Changes between OSPF for IPv4, OSPF Version 2, and OSPF for IPv6 as described herein include the following. Addressing semantics have been removed from OSPF packets and the basic Link State Advertisements (LSAs). New LSAs have been created to carry IPv6 addresses and prefixes. OSPF now runs on a per-link basis rather than on a per-IP-subnet basis. Flooding scope for LSAs has been generalized. Authentication has been removed from the OSPF protocol and instead relies on IPv6's Authentication Header and Encapsulating Security Payload (ESP). Even with larger IPv6 addresses, most packets in OSPF for IPv6 are almost as compact as those in OSPF for IPv4. Most fields and packet- size limitations present in OSPF for IPv4 have been relaxed. In addition, option handling has been made more flexible. All of OSPF for IPv4's optional capabilities, including demand circuit support and Not-So-Stubby Areas (NSSAs), are also supported in OSPF for IPv6. [STANDARDS-TRACK] This document specifies the Path Computation Element (PCE) Communication Protocol (PCEP) for communications between a Path Computation Client (PCC) and a PCE, or between two PCEs. Such interactions include path computation requests and path computation replies as well as notifications of specific states related to the use of a PCE in the context of Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering. PCEP is designed to be flexible and extensible so as to easily allow for the addition of further messages and objects, should further requirements be expressed in the future. [STANDARDS-TRACK] The Network Configuration Protocol (NETCONF) defined in this document provides mechanisms to install, manipulate, and delete the configuration of network devices. It uses an Extensible Markup Language (XML)-based data encoding for the configuration data as well as the protocol messages. The NETCONF protocol operations are realized as remote procedure calls (RPCs). This document obsoletes RFC 4741. [STANDARDS-TRACK] This document describes Path MTU Discovery (PMTUD) for IP version 6. It is largely derived from RFC 1191, which describes Path MTU Discovery for IP version 4. It obsoletes RFC 1981. This document identifies a need for and proposes improvement of the unicast Reverse Path Forwarding (uRPF) techniques (see RFC 3704) for detection and mitigation of source address spoofing (see BCP 38). Strict uRPF is inflexible about directionality, the loose uRPF is oblivious to directionality, and the current feasible-path uRPF attempts to strike a balance between the two (see RFC 3704). However, as shown in this document, the existing feasible-path uRPF still has shortcomings. This document describes enhanced feasible-path uRPF (EFP-uRPF) techniques that are more flexible (in a meaningful way) about directionality than the feasible-path uRPF (RFC 3704). The proposed EFP-uRPF methods aim to significantly reduce false positives regarding invalid detection in source address validation (SAV). Hence, they can potentially alleviate ISPs' concerns about the possibility of disrupting service for their customers and encourage greater deployment of uRPF techniques. This document updates RFC 3704.

CRH Processing Examples This appendix demonstrates CRH processing in the following scenarios:

• The CRH SID list contains one entry for each segment in the path ().
• The CRH SID list omits the first entry in the path ().

provides a reference topology that is used in all examples, and describes two entries that appear in each node's CRH-FIB.

Reference Topology ----------- ----------- ----------- |Node: S | |Node: I1 | |Node: I2 | |Loopback: |---------------|Loopback: |---------------|Loopback: | |2001:db8::a| |2001:db8::1| |2001:db8::2| ----------- ----------- ----------- | | | ----------- | | |Node: D | | ---------------------|Loopback: |--------------------- |2001:db8::b| -----------

Node SIDs

SID	IPv6 Address	Forwarding Method
2	2001:db8::2	Least-cost path
11	2001:db8::b	Least-cost path

The CRH SID list contains one entry for each segment in the path. In this example, Node S sends a packet to Node D via I2, and I2 appears in the CRH segment list. Packet Travels from S to I2

Source Address = 2001:db8::a	Segments Left = 1
Destination Address = 2001:db8::2	SID[0] = 11
	SID[1] = 2

Packet Travels from I2 to D

Source Address = 2001:db8::a	Segments Left = 0
Destination Address = 2001:db8::b	SID[0] = 11
	SID[1] = 2

The CRH SID list omits the first entry in the path. In this example, Node S sends a packet to Node D via I2, and I2 does not appear in the CRH segment list. Packet Travels from S to I2

Source Address = 2001:db8::a	Segments Left = 1
Destination Address = 2001:db8::2	SID[0] = 11

Packet Travels from I2 to D

Source Address = 2001:db8::a	Segments Left = 0
Destination Address = 2001:db8::b	SID[0] = 11

Acknowledgements Thanks to , , , , , , , , , , , , , , and for their contributions to this document.

Contributors Baidu

No.10 Xibeiwang East Road Beijing Haidian District 100193 China phdgang@gmail.com

ByteDance

43 N 3rd Ring W Rd Building 1, AVIC Plaza Haidian District Beijing 100000 China yifeng.zhou@bytedance.com

Verizon

Silver Spring MD United States of America hayabusagsm@gmail.com

Authors' Addresses Juniper Networks

2251 Corporate Park Drive Herndon 20171 VA United States of America rbonica@juniper.net

NTT Communications Corporation

3-4-1 Shibaura, Minato-ku Tokyo 108-8118 Japan y.kamite@ntt.com

Alston Networks

Nairobi Kenya aa@alstonnetworks.net

Liquid Telecom

Johannesburg South Africa daniam.henriques@liquidtelecom.com

Verizon

Richardson TX United States of America luay.jalil@one.verizon.com