Internet-Draft | IPv6 Compressed Routing Header | May 2022 |
Bonica, et al. | Expires 18 November 2022 | [Page] |
- Workgroup:
- 6man
- Internet-Draft:
- draft-bonica-6man-comp-rtg-hdr-28
- Published:
- Intended Status:
- Standards Track
- Expires:
The IPv6 Compact Routing Header (CRH)
Abstract
This document defines two new Routing header types. Collectively, they are called the Compact Routing Headers (CRH). Individually, they are called CRH-16 and CRH-32.¶
Status of This Memo
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This Internet-Draft will expire on 18 November 2022.¶
Copyright Notice
Copyright (c) 2022 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 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.¶
1. Introduction
IPv6 [RFC8200] source nodes use Routing headers to specify the path that a packet takes to its destination. The IETF has defined several Routing header types [IANA-RH]. This document defines two new Routing header types. Collectively, they are called the Compact Routing Headers (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.¶
- Is designed to operate within a limited domain. (See Section 9).¶
The following are reasons for encoding the CRH in as few bytes as possible:¶
- Many ASIC-based forwarders 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) [RFC8201] 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.¶
2. 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. The Compressed Routing Headers (CRH)
Both CRH versions (i.e., CRH-16 and CRH-32) contain the following fields:¶
- Next Header - Defined in [RFC8200].¶
- Hdr Ext Len - Defined in [RFC8200].¶
- Routing Type - Defined in [RFC8200]. (CRH-16 value is 5. CRH-32 value is 6).¶
- Segments Left - Defined in [RFC8200].¶
- Type-specific Data - Described in [RFC8200].¶
In the CRH, the Type-specific data field contains a list of Segment Identifiers (SIDs). Each SID represents both of the following:¶
- A segment of the path that the packet takes to its destination.¶
- An entry in the CRH Forwarding Information Base (CRH-FIB) (Section 4).¶
SIDs are listed in reverse order. So, the first SID in the list represents the final segment in the path. Because segments are listed in reverse order, the Segments Left field can be used as an index into the SID list. In this document, the "current SID" is the SID list entry referenced by the Segments Left field.¶
The first segment in the path can be omitted from the list. See Appendix A for examples.¶
In the CRH-16 (Figure 1), each SID is encoded in 16-bits. In the CRH-32 (Figure 2), each 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.¶
4. The CRH Forwarding Information Base (CRH-FIB)
Each SID identifies a CRH-FIB entry.¶
Each CRH-FIB entry contains:¶
The first ten bits of the IPv6 address MUST NOT be fe00. That prefix is reserved for link-local [RFC6890] addresses.¶
The topological function specifies how the processing node forwards the packet to the next segment endpoint. The following are examples:¶
- Forward the packet through the least-cost path to the next segment endpoint.¶
- Forward the packet through a specified interface.¶
- Encapsulate the packet in another IPv6 header of any type (e.g., MPLS, IPv6) and forward either through the least cost path or a specified interface.¶
Some topological functions require parameters. For example, a topological function might require a parameter that identifies the interface through which the packet should be forwarded.¶
The CRH-FIB can be populated:¶
- By an operator, using a Command Line Interface (CLI).¶
- By a controller, using the Path Computation Element (PCE) Communication Protocol (PCEP) [RFC5440] or the Network Configuration Protocol (NETCONF) [RFC6241].¶
- By a distributed routing protocol [ISO10589-Second-Edition], [RFC5340], [RFC4271].¶
5. Processing Rules
The following rules describe CRH processing:¶
- If Segments Left equals 0, skip over the CRH and process the next header in the packet.¶
- If Hdr Ext Len indicates that the CRH is larger than the implementation can process, discard the packet and send an ICMPv6 [RFC4443] Parameter Problem, Code 0, message to the Source Address, pointing to the Hdr Ext Len field.¶
- Compute L, the minimum CRH length ( Section 5.1).¶
- If L is greater than Hdr Ext Len, discard the packet and send an ICMPv6 Parameter Problem, Code 0, message to the Source Address, pointing to the Segments Left field.¶
- Decrement Segments Left.¶
- Search for the current SID in the CRH-FIB. In this document, the "current SID" is the 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.¶
- Copy the IPv6 address from the CRH-FIB entry to the Destination Address field in the IPv6 header.¶
- Decrement the IPv6 Hop Limit.¶
- Submit the packet, its topological function and its parameters to the IPv6 module. See NOTE.¶
NOTE: By default, the IPv6 module determines the next-hop and forwards the packet. However, the topological function may elicit another behavior. For example, the IPv6 module may forward the packet through a specified interface.¶
5.1. Computing Minimum CRH Length
The algorithm described in this section accepts the following CRH fields as its input parameters:¶
It yields L, the minimum CRH length. The minimum CRH length is measured in 8-octet units, not including the first 8 octets.¶
<CODE BEGINS> 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) <CODE ENDS>¶
6. Mutability
In the CRH, the Segments Left field is mutable. All remaining fields are immutable.¶
7. Applications And SIDs
A CRH contains one or more SIDs. Each SID is processed by exactly one node.¶
Therefore, a SID is not required to have domain-wide significance. Applications can:¶
8. Management Considerations
PING and TRACEROUTE [RFC2151] both operate correctly in the presence of the CRH.¶
9. Security Considerations
Networks that process the CRH MUST NOT accept packets containing the CRH from outside of there limited domain.. Their border routers SHOULD discard packets that satisfy the following criteria:¶
- The packet contains a CRH¶
- The Segments Left field in the CRH has a value greater than 0¶
- The Destination Address field in the IPv6 header represents an interface that resides inside of the network.¶
Many border routers cannot filter packets based upon the Segments Left value. These border routers MAY discard packets that satisfy the following criteria:¶
10. Implementation and Deployment Status
Juniper Networks has produced experimental implementations of the CRH on:¶
Liquid Telecom has deployed the CRH, on a limited basis, in their network. Other experimental deployments are in progress.¶
11. IANA Considerations
This document makes the following registrations in the "Internet Protocol Version 6 (IPv6) Parameters" "Routing Types" subregistry maintained by IANA:¶
+-------+------------------------------+---------------+ | Value | Description | Reference | +=======+==============================+===============+ | 5 | CRH-16 | This document | +-------+------------------------------+---------------+ | 6 | CRH-32 | This document | +-------+------------------------------+---------------+¶
12. Acknowledgements
Thanks to Dr. Vanessa Ameen, Fernando Gont, Naveen Kottapalli, Joel Halpern, Tony Li, Gerald Schmidt, Nancy Shaw, Ketan Talaulikar, and Chandra Venkatraman for their contributions to this document.¶
13. Contributors
- Gang Chen¶
- Baidu¶
- No.10 Xibeiwang East Road Haidian District¶
- Beijing 100193 P.R. China¶
- Email: phdgang@gmail.com¶
- Yifeng Zhou¶
- ByteDance¶
- Building 1, AVIC Plaza, 43 N 3rd Ring W Rd Haidian District¶
- Beijing 100000 P.R. China¶
- Email: yifeng.zhou@bytedance.com¶
14. References
14.1. Normative References
- [RFC2119]
- Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
- [RFC4443]
- Conta, A., Deering, S., and M. Gupta, Ed., "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", STD 89, RFC 4443, DOI 10.17487/RFC4443, , <https://www.rfc-editor.org/info/rfc4443>.
- [RFC8174]
- Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <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, , <https://www.rfc-editor.org/info/rfc8200>.
- [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, , <https://www.rfc-editor.org/info/rfc8201>.
14.2. Informative References
- [IANA-RH]
- IANA, "Routing Headers", <https://www.iana.org/assignments/ipv6-parameters/ipv6-parameters.xhtml#ipv6-parameters-3>.
- [ISO10589-Second-Edition]
- International Organization for Standardization, ""Intermediate system to Intermediate system intra-domain routeing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode Network Service (ISO 8473)", ISO/IEC 10589:2002, Second Edition,", .
- [RFC2151]
- Kessler, G. and S. Shepard, "A Primer On Internet and TCP/IP Tools and Utilities", FYI 30, RFC 2151, DOI 10.17487/RFC2151, , <https://www.rfc-editor.org/info/rfc2151>.
- [RFC4271]
- Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, , <https://www.rfc-editor.org/info/rfc4271>.
- [RFC5340]
- Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, DOI 10.17487/RFC5340, , <https://www.rfc-editor.org/info/rfc5340>.
- [RFC5440]
- Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, , <https://www.rfc-editor.org/info/rfc5440>.
- [RFC6241]
- Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, , <https://www.rfc-editor.org/info/rfc6241>.
- [RFC6890]
- Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, "Special-Purpose IP Address Registries", BCP 153, RFC 6890, DOI 10.17487/RFC6890, , <https://www.rfc-editor.org/info/rfc6890>.
Appendix A. CRH Processing Examples
This appendix demonstrates CRH processing in the following scenarios:¶
- The SID list contains one entry for each segment in the path (Appendix A.1).¶
- The SID list omits the first entry in the path (Appendix A.2).¶
Figure 3 provides a reference topology that is used in all examples.¶
SID | IPv6 Address | Forwarding Method |
---|---|---|
2 | 2001:db8::2 | Least-cost path |
11 | 2001:db8::b | Least-cost path |
Table 1 describes two entries that appear in each node's CRH-FIB.¶
A.1. The SID List Contains One Entry For Each Segment In The Path
In this example, Node S sends a packet to Node D, via I2. In this example, I2 appears in the CRH segment list.¶
As the 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 |
As the 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 |
A.2. The SID List Omits The First Entry In The Path
In this example, Node S sends a packet to Node D, via I2. In this example, I2 does not appear in the CRH segment list.¶
As the packet travels from S to I2: | |
---|---|
Source Address = 2001:db8::a | Segments Left = 1 |
Destination Address = 2001:db8::2 | SID[0] = 11 |
As the packet travels from I2 to D: | |
---|---|
Source Address = 2001:db8::a | Segments Left = 0 |
Destination Address = 2001:db8::b | SID[0] = 11 |