The IPv6 Compact Routing Header (CRH)

Abstract

This document describes an experiment in which two new IPv6 Routing headers are implemented and deployed. Collectively, they are called the Compact Routing Headers (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. Finally, this document encourages replication of the experiment.¶

3. The Compact 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 CRH Segment Identifiers (CRH SIDs). Each CRH SID identifies an entry in the CRH Forwarding Information Base (CRH-FIB) (Section 4). 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 can be omitted from the list. See Appendix A for an example.¶

In the CRH-16 (Figure 1), each CRH SID is encoded in 16-bits. In the CRH-32 (Figure 2), 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.¶

   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]               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
  |                          .........
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   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]                            +
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  //                                                              //
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  +                             SID[n]                            +
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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. The IPv6 address in the IPv6 Header's Destination Address field is that of the ultimate recipient.¶

• 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 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.¶

• 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.¶

<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. Destination Address Transparency

When a packet containing the CRH header leaves its source, it does not include its final destination address. The final destination address is not added to the packet until the final CRH SID is resolved.¶

While destination address transparency enhances privacy, it prevents intermediate nodes from verifying transport layer checksums.¶

8. Applications And SIDs

A CRH contains one or more CRH SIDs. Each CRH SID is processed by exactly one node.¶

Therefore, a CRH SID is not required to have domain-wide significance. Applications can:¶

• Allocate CRH SIDs so that they have domain-wide significance.¶

• Allocate CRH SIDs so that they have node-local significance.¶

9. Management Considerations

PING and TRACEROUTE [RFC2151] 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 text representations described herein.¶

10. ICMPv6 Considerations

A node can emit ICMPv6 messages when processing a packet that contains the CRH. The following are ICMPv6 considerations:¶

• ICMPv6 messages are subject to rate limits.¶

• ICMPv6 message delivery is not reliable.¶

• ICMPv6 messages are easily forged.¶

• Most ICMPv6 implementations process all ICMPv6 Parameter Problem messages identically, regardless of the pointer value.¶

11. Textual Representation

A 16-bit CRH SID can be represented by four 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 hexadecimal digits, a colon (:), and another four 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 represent in dotted-decimal notation. The following are examples:¶

• 192.0.2.1¶

• 192.0.2.2¶

• 192.0.2.3¶

13. Implementation and Deployment Status

Juniper Networks has produced experimental implementations of the CRH on the MX-series (ASIC-based) router¶

Liquid Telecom has produced experimental implementations of the CRH on software based routers.¶

The CRH has carried non-production traffic in CERNET and Liquid Telecom.¶

Interoperability among these implementations has not yet been demonstrated.¶

14. 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 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 FIB¶

• Scale of deployment¶

• Interoperability¶

  • Did you deploy two inter-operable 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 OAM mechanism¶

  • Did PING work?¶

  • Did TRACEROUTE work?¶

  • Did Wireshark work?¶

  • Did TCPDUMP work?¶

15. 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 |
         +-------+------------------------------+---------------+

17. 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¶

• ¶

• Gyan Mishra¶

• Verizon¶

• Silver Spring, Maryland, USA¶

• Email: hayabusagsm@gmail.com¶

18. References