]> 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.

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

CRH-32

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.

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 Informative References IANA ISO/IEC Second Edition

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 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