Internet-Draft Join-Proxy September 2020
Richardson, et al. Expires 26 March 2021 [Page]
anima Working Group
Intended Status:
Standards Track
M. Richardson
Sandelman Software Works
P. van der Stok
vanderstok consultancy
P. Kampanakis
Cisco Systems

Constrained Join Proxy for Bootstrapping Protocols


This document defines a protocol to securely assign a pledge to an owner, using an intermediary node between pledge and owner. This intermediary node is known as a "constrained Join Proxy".

This document extends the work of [I-D.ietf-anima-bootstrapping-keyinfra] by replacing the Circuit-proxy by a stateless constrained (CoAP) Join Proxy. It transports join traffic from the pledge to the Registrar without requiring per-client state.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 26 March 2021.

Table of Contents

1. Introduction

Enrolment of new nodes into constrained networks with constrained nodes present is described in [I-D.ietf-anima-bootstrapping-keyinfra] ("BRSKI") and makes use of Enrolment over Secure Transport (EST) [RFC7030] with [RFC8366] vouchers to securely enroll devices. BRSKI connects new devices ("pledges") to extended EST servers ("Registrars") via a Join Proxy.

The specified solutions use https and may be too large in terms of code space or bandwidth required. Constrained devices in constrained networks [RFC7228] typically implement the IPv6 over Low-Power Wireless personal Area Networks (6LoWPAN) [RFC4944] and Constrained Application Protocol (CoAP) [RFC7252].

CoAP can be run with the Datagram Transport Layer Security (DTLS) [RFC6347] as a security protocol for authenticity and confidentiality of the messages. This is described as the "coaps" scheme. A constrained version of EST, using Coap and DTLS, is described in [I-D.ietf-ace-coap-est].

DTLS is a client-server protocol relying on the underlying IP layer to perform the routing between the DTLS Client and the DTLS Server. However, the new "joining" device will not be IP routable until it is authenticated to the network. A new "joining" device can only initially use a link-local IPv6 address to communicate with a neighbour node using neighbour discovery [RFC6775] until it receives the necessary network configuration parameters. However, before the device can receive these configuration parameters, it needs to authenticate itself to the network to which it connects. IPv6 routing is necessary to establish a connection between joining device and the extended EST server.

This document specifies a new form of Join Proxy and protocol to act as intermediary between joining device and EST server to establish a connection between joining device and EST server.

This document is very much inspired by text published earlier in [I-D.kumar-dice-dtls-relay]. [I-D.richardson-anima-state-for-joinrouter] outlined the various options for building a join proxy. [I-D.ietf-anima-bootstrapping-keyinfra] adopted only the Circuit Proxy method (1), leaving the other methods as future work. The document standardizes the CoAP/DTLS (method 4).

2. Terminology

The following terms are defined in [RFC8366], and are used identically as in that document: artifact, imprint, domain, Join Registrar/Coordinator (JRC), Manufacturer Authorized Signing Authority (MASA), pledge, Trust of First Use (TOFU), and Voucher.

3. 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.

4. Join Proxy functionality

As depicted in the Figure 1, the joining Device, or pledge (P), in an LLN mesh is more than one hop away from the EST server (E) and not yet authenticated into the network.

At this stage, it can only communicate one-hop to its nearest neighbour, the Join Proxy (J) using their link-local IPv6 addresses. However, the Pledge (P) needs to communicate with end-to-end security with a Registrar hosting the EST server (E) to authenticate and get the relevant system/network parameters. If the Pledge (P) initiates a DTLS connection to the EST server whose IP address has been pre-configured, then the packets are dropped at the Join Proxy (J) since the Pledge (P) is not yet admitted to the network or there is no IP routability to Pledge (P) for any returned messages.

          ++++ multi-hop
          |E |---- mesh  +--+        +--+
          |  |    \      |J |........|P |
          ++++     \-----|  |        |  |
       EST server        +--+        +--+
       Registrar       Join Proxy   Pledge
                                    "Joining" Device

Figure 1: multi-hop enrolment.

Furthermore, the Pledge (P) may wish to establish a secure connection to the EST server (E) in the network assuming appropriate credentials are exchanged out-of-band, e.g. a hash of the Pledge (P)'s raw public key could be provided to the EST server (E). However, the Pledge (P) may be unaware of the IP address of the EST-server (E) to initiate a DTLS connection and perform authentication with.

A DTLS connection is required between Pledge and EST server. To overcome the problems with non-routability of DTLS packets and/or discovery of the destination address of the EST Server to contact, the Join Proxy is introduced. This Join Proxy functionality is configured into all authenticated devices in the network which may act as the Join Proxy for newly joining nodes. The Join Proxy allows for routing of the packets from the Pledge using IP routing to the intended EST Server.

5. Join Proxy specification

A Join Proxy can operate in two modes:

5.1. Statefull Join Proxy

In stateful mode, the joining node forwards the DTLS messages to the BRSKI Registrar.

Assume that the Pledge does not know the IP address of the EST Server it needs to contact. In that situation, the Join Proxy must know the (configured or discovered) IP address of a BRSKI Registrar. (Discovery can be based upon [I-D.ietf-anima-bootstrapping-keyinfra] section 4.3, or via DNS-SD service discovery [RFC6763]) The Pledge initiates its request as if the Join Proxy is the intended Registrar. The Join Proxy changes the IP packet (without modifying the DTLS message) as in the previous case by modifying both the source and destination addresses to forward the message to the intended EST Server. The Join Proxy maintains a 4-tuple array to translate the DTLS messages received from the EST Server and forward it to the EST Client. This is a form of Network Address translation, where the Join Proxy acts as a forward proxy. In Figure 2 the various steps of the message flow are shown:

| EST Client | Join Proxy | EST Server  |          Message         |
|    (P)     |     (J)    |    (E)      | Src_IP:port | Dst_IP:port|
|      --ClientHello-->                 |   IP_P:p_P  | IP_Ja:5684 |
|                    --ClientHello-->   |   IP_Jb:p_Jb| IP_E:5684  |
|                                       |             |            |
|                    <--ServerHello--   |   IP_E:5684 | IP_Jb:p_Jb |
|                            :          |             |            |
|       <--ServerHello--     :          |   IP_Ja:5684| IP_P:p_P   |
|               :            :          |             |            |
|               :            :          |       :     |    :       |
|               :            :          |       :     |    :       |
|        --Finished-->       :          |   IP_P:p_P  | IP_Ja:5684 |
|                      --Finished-->    |   IP_Jb:p_Jb| IP_E:5684  |
|                                       |             |            |
|                      <--Finished--    |   IP_E:5684 | IP_Jb:p_Jb |
|        <--Finished--                  |   IP_Ja:5684| IP_P:p_P   |
|              :             :          |      :      |     :      |
IP_P:p_P = Link-local IP address and port of Pledge (DTLS Client)
IP_E:5684 = Global IP address and coaps port of EST Server
IP_Ja:5684 = Link-local IP address and coaps port of Join Proxy
IP_Jb:p_Rb = Global IP address and port of Join proxy
Figure 2: constrained statefull joining message flow with EST server address known to Join Proxy.

5.2. Stateless Join Proxy

The Join Proxy is stateless to minimize the requirements on the constrained Join Proxy device. Stateless operation requires no memory in the Join Proxy device, but may also reduce the CPU impact as the device does not need to search through a state table.

When a joining device as a client attempts a DTLS connection to the EST server, it uses its link-local IP address as its IP source address. This message is transmitted one-hop to a neighbouring (join proxy) node. Under normal circumstances, this message would be dropped at the neighbour node since the joining device is not yet IP routable or it is not yet authenticated to send messages through the network. However, if the neighbour device has the Join Proxy functionality enabled, it routes the DTLS message to a specific Registrar. Additional security mechanisms need to exist to prevent this routing functionality being used by rogue nodes to bypass any network authentication procedures.

If an untrusted DTLS Client that can only use link-local addressing wants to contact a trusted end-point Registrar, it sends the DTLS message to the Join Proxy.

The Join Proxy extends this message into a new type of message called Join ProxY (JPY) message and sends it on to the Registrar.

The JPY message payload consists of two parts:

  • Header (H) field: consisting of the source link-local address and port of the Pledge (P), and
  • Contents (C) field: containing the original DTLS message.

On receiving the JPY message, the BRSKI Registrar retrieves the two parts.

The BRSKI server transiently stores the Header field information. The Registrar server uses the Contents field to execute the Registrar server functionality. However, when the Registrar replies, it also extends its DTLS message with the header field in a JPY message and sends it back to the Join Proxy. The Registrar SHOULD NOT assume that it can decode the Header Field, it should simply repeat it when responding. The Header contains the original source link-local address and port of the DTLS Client from the transient state stored earlier (which can now be discarded) and the Contents field contains the DTLS message.

On receiving the JPY message, the Join Proxy retrieves the two parts. It uses the Header field to route the DTLS message retrieved from the Contents field to the Pledge.

The Figure 3 depicts the message flow diagram:

| EST  Client  | Join Proxy |    EST server |        Message        |
|     (P)      |     (J)    |      (E)      |Src_IP:port|Dst_IP:port|
|      --ClientHello-->                     | IP_P:p_P  |IP_Ja:5684 |
|                    --JPY[H(IP_P:p_P),-->  | IP_Jb:p_Jb|IP_E:5684  |
|                          C(ClientHello)]  |           |           |
|                    <--JPY[H(IP_P:p_P),--  | IP_E:5684 |IP_Jb:p_Jb |
|                         C(ServerHello)]   |           |           |
|      <--ServerHello--                     | IP_Ja:5684|IP_P:p_P   |
|              :                            |           |           |
|              :                            |     :     |    :      |
|                                           |     :     |    :      |
|      --Finished-->                        | IP_P:p_P  |IP_Ja:5684 |
|                    --JPY[H(IP_P:p_P),-->  | IP_Jb:p_Jb|IP_E:5684  |
|                          C(Finished)]     |           |           |
|                    <--JPY[H(IP_P:p_P),--  | IP_E:5684 |IP_Jb:p_Jb |
|                         C(Finished)]      |           |           |
|      <--Finished--                        | IP_Ja:5684|IP_P:p_P   |
|              :                            |     :     |    :      |
IP_P:p_P = Link-local IP address and port of the Pledge
IP_E:5684 = Global IP address and coaps port of EST Server
IP_Ja:5684 = Link-local IP address and coaps port of Join Proxy
IP_Jb:p_Jb = Global IP address and port of Join Proxy

JPY[H(),C()] = Join Proxy message with header H and content C

Figure 3: constrained stateless joining message flow.

5.3. Stateless Message structure

The JPY message is constructed as a payload with media-type application/multipart-core specified in [I-D.ietf-core-multipart-ct].

Header and Contents fields use different media formats:

  1. header field: application/cbor containing a CBOR array [RFC7049] with the pledge IPv6 Link Local address as a 16-byte binary value, the pledge's UDP port number, if different from 5684, as a CBOR integer, and the proxy's ifindex or other identifier for the physical port on which the pledge is connected. Header is not DTLS encrypted.
  2. Content field: Any of the media types specified in [I-D.ietf-ace-coap-est] and [I-D.ietf-anima-constrained-voucher] dependent on the function that is requested:
 * application/pkcs7-mime; smime-type=server-generated-key
 * application/pkcs7-mime; smime-type=certs-only
 * application/voucher-cms+cbor
 * application/voucher-cose+cbor
 * application/pkcs8
 * application/csrattrs
 * application/pkcs10
 * application/pkix-cert

(XXX- add CDDL for CBOR array above)

The content fields are DTLS encrypted. In CBOR diagnostic notation the payload JPY[H(IP_P:p_P), with cf is content-format of DTLS-content, will look like:

      [ 60: [IP_p, p_P, ident]
        cf: h'DTLS-content']

Examples are shown in Appendix A.

6. Comparison of stateless and statefull modes

The stateful and stateless mode of operation for the Join Proxy have their advantages and disadvantages. This section should enable to make a choice between the two modes based on the available device resources and network bandwidth.

| Properties  |         Stateful mode      |     Stateless mode     |
| State       |The Join Proxy needs        | No information is      |
| Information |additional storage to       | maintained by the Join |
|             |maintain mapping between    | Proxy                  |
|             |the address and port number |                        |
|             |of the pledge and those     |                        |
|             |of the EST-server.          |                        |
|Packet size  |The size of the forwarded   |Size of the forwarded   |
|             |message is the same as the  |message is bigger than  |
|             |original message.           |the original,it includes|
|             |                            |additional source and   |
|             |                            |destination addresses.  |
|Specification|The Join Proxy needs        |New JPY message to      |
|complexity   |additional functionality    |encapsulate DTLS message|
|             |to maintain state           |The EST server          |
|             |information, and modify     |and the Join Proxy      |
|             |the source and destination  |have to understand the  |
|             |addresses of the DTLS       |JPY message in order    |
|             |handshake messages          |to process it.          |
Figure 4: Comparison between stateful and stateless mode

7. Discovery

It is assumed that Join Proxy seamlessly provides a coaps connection between Pledge and coaps EST-server. An additional Registrar is needed to connect the Pledge to an http EST server, see section 8 of [I-D.ietf-ace-coap-est]. In particular this section replaces section 4.2 of [I-D.ietf-anima-bootstrapping-keyinfra].

Three discovery cases are discussed: coap discovery, 6tisch discovery and GRASP discovery.

7.1. Pledge discovery of Join Proxy

The pledge and Join Proxy are assumed to communicate via Link-Local addresses.

7.1.1. CoAP discovery

The discovery of the coaps EST server, using coap discovery, by the Join Proxy follows section 6 of [I-D.ietf-ace-coap-est].

7.1.2. Autonomous Network

In the context of autonomous networks, the Join Proxy uses the DULL GRASP M_FLOOD mechanism to announce itself. Section 4.1.1 of [I-D.ietf-anima-bootstrapping-keyinfra] discusses this in more detail. The Registrar announces itself using ACP instance of GRASP using M_FLOOD messages. Autonomous Network Join Proxies MUST support GRASP discovery of EST-server as decribed in section 4.3 of [I-D.ietf-anima-bootstrapping-keyinfra] .

7.1.3. 6tisch discovery

The discovery of EST server by the pledge uses the enhanced beacons as discussed in [I-D.ietf-6tisch-enrollment-enhanced-beacon].

7.2. Join Proxy discovers EST server

7.2.1. Autonomous Network

The pledge MUST listen for GRASP M_FLOOD [I-D.ietf-anima-grasp] announcements of the objective: "AN_Proxy". See section Section 4.1.1 [I-D.ietf-anima-bootstrapping-keyinfra] for the details of the objective.

7.2.2. CoAP discovery

In the context of a coap network without Autonomous Network support, discovery follows the standard coap policy. The Pledge can discover a Join Proxy by sending a link-local multicast message to ALL CoAP Nodes with address FF02::FD. Multiple or no nodes may respond. The handling of multiple responses and the absence of responses follow section 4 of [I-D.ietf-anima-bootstrapping-keyinfra].

The presence and location of (path to) the Join Proxy resource are discovered by sending a GET request to "/.well-known/core" including a resource type (rt) parameter with the value "brski-proxy" [RFC6690]. Upon success, the return payload will contain the root resource of the Join Proxy resources. It is up to the implementation to choose its root resource; throughout this document the example root resource /jp is used. The example below shows the discovery of the presence and location of Join Proxy resources.

  REQ: GET coap://[FF02::FD]/.well-known/core?rt=brski-proxy

  RES: 2.05 Content
  </jp>; rt="brski-proxy";ct=62

Port numbers, not returned in the example, are assumed to be the default numbers 5683 and 5684 for coap and coaps respectively (sections 12.6 and 12.7 of [RFC7252]. Discoverable port numbers MAY be returned in the <href> of the payload (see section 5.1 of [I-D.ietf-ace-coap-est]).

8. Security Considerations

It should be noted here that the contents of the CBOR map used to convey return address information is not protected. However, the communication is between the Proxy and a known registrar are over the already secured portion of the network, so are not visible to eavesdropping systems.

All of the concerns in [I-D.ietf-anima-bootstrapping-keyinfra] section 4.1 apply. The pledge can be deceived by malicious AN_Proxy announcements. The pledge will only join a network to which it receives a valid [RFC8366] voucher.

If the proxy/Registrar was not over a secure network, then an attacker could change the cbor array, causing the pledge to send traffic to another node. If the such scenario needed to be supported, then it would be reasonable for the Proxy to encrypt the CBOR array using a locally generated symmetric key. The Registrar would not be able to examine the result, but it does not need to do so. This is a topic for future work.

9. IANA Considerations

This document needs to create a registry for key indices in the CBOR map. It should be given a name, and the amending formula should be IETF Specification.

9.1. Resource Type registry

This specification registers a new Resource Type (rt=) Link Target Attributes in the "Resource Type (rt=) Link Target Attribute Values" subregistry under the "Constrained RESTful Environments (CoRE) Parameters" registry.

  rt="brski-proxy". This EST resource is used to query and return
  the supported EST resource of a Join Proxy placed between Pledge
  and EST server.

10. Acknowledgements

Many thanks for the comments by Brian Carpenter.

11. Contributors

Sandeep Kumar, Sye loong Keoh, and Oscar Garcia-Morchon are the co-authors of the draft-kumar-dice-dtls-relay-02. Their draft has served as a basis for this document. Much text from their draft is copied over to this draft.

12. Changelog

12.1. 01 to 02

  • extended the discovery section
  • removed inconsistencies from the the flow diagrams
  • Improved readability of the examples.
  • stateful configurations reduced to one

12.2. 00 to 01

  • Added Contributors section
  • Adapted content-formats to est-coaps formats
  • Aligned examples with est-coaps examples
  • Added statefull Proxy to stateless proxy

12.3. 00 to 00

  • added payload examples in appendix
  • discovery for three cases: AN, 6tisch and coaps

13. References

13.1. Normative References

Dujovne, D. and M. Richardson, "IEEE 802.15.4 Information Element encapsulation of 6TiSCH Join and Enrollment Information", Work in Progress, Internet-Draft, draft-ietf-6tisch-enrollment-enhanced-beacon-14, , <>.
Stok, P., Kampanakis, P., Richardson, M., and S. Raza, "EST over secure CoAP (EST-coaps)", Work in Progress, Internet-Draft, draft-ietf-ace-coap-est-18, , <>.
Pritikin, M., Richardson, M., Eckert, T., Behringer, M., and K. Watsen, "Bootstrapping Remote Secure Key Infrastructures (BRSKI)", Work in Progress, Internet-Draft, draft-ietf-anima-bootstrapping-keyinfra-44, , <>.
Richardson, M., Stok, P., and P. Kampanakis, "Constrained Voucher Artifacts for Bootstrapping Protocols", Work in Progress, Internet-Draft, draft-ietf-anima-constrained-voucher-08, , <>.
Bormann, C., Carpenter, B., and B. Liu, "A Generic Autonomic Signaling Protocol (GRASP)", Work in Progress, Internet-Draft, draft-ietf-anima-grasp-15, , <>.
Fossati, T., Hartke, K., and C. Bormann, "Multipart Content-Format for CoAP", Work in Progress, Internet-Draft, draft-ietf-core-multipart-ct-04, , <>.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, , <>.
Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Watsen, K., Richardson, M., Pritikin, M., and T. Eckert, "A Voucher Artifact for Bootstrapping Protocols", RFC 8366, DOI 10.17487/RFC8366, , <>.

13.2. Informative References

Stajano, F. and R. Anderson, "The resurrecting duckling: security issues for ad-hoc wireless networks", , <>.
Kumar, S., Keoh, S., and O. Garcia-Morchon, "DTLS Relay for Constrained Environments", Work in Progress, Internet-Draft, draft-kumar-dice-dtls-relay-02, , <>.
Richardson, M., "Considerations for stateful vs stateless join router in ANIMA bootstrap", Work in Progress, Internet-Draft, draft-richardson-anima-state-for-joinrouter-02, , <>.
[pledge], ., " Unabridged", , <>.
Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, DOI 10.17487/RFC4944, , <>.
Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, , <>.
Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", RFC 6763, DOI 10.17487/RFC6763, , <>.
Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. Bormann, "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)", RFC 6775, DOI 10.17487/RFC6775, , <>.
Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., "Enrollment over Secure Transport", RFC 7030, DOI 10.17487/RFC7030, , <>.
Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, , <>.
Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, , <>.

Appendix A. Stateless Proxy payload examples

Examples are extensions of two examples shown in [I-D.ietf-ace-coap-est]. The following content formats are used:

For presentation purposes the payloads are abbreviated as follows:

cacrts request payload:

   <cacrts request payload> = <empty>

cacrts response payload:

   <cacrts response payload> =

serverkeygen request payload:

   <serverkeygen request payload> =

serverkeygen response payload:

   <serverkeygen response payload> =
   84                                   # array(4)
   19 011C                              # unsigned(284)
   58 8A                                # bytes(138)
   19 0119                              # unsigned(281)
   59 01D3                              # bytes(467)

A.1. cacerts

The request from Join Proxy to EST-server looks like:

    Get coaps://
    (Accept: 62)
    (Content-format: 62)
    payload =
    82                    # array(2)
    18 3C                 # unsigned(60)
    83                    # array(3)
    69                    # text(9)
         464538303A3A414238 # "FE80::AB8"
    19 237D               # unsigned(9085)
    65                    # text(5)
         6964656E74       # "ident"

In CBOR Diagnostic:

    payload = [60, ["FE80::AB8", 9085, "ident"]]

The response will then be:

     2.05 Content
     (Content-format: 62)
       Payload =
     84                                # array(4)
     18 3C                             # unsigned(60)
     83                                # array(3)
     69                                # text(9)
         464538303A3A414238            # "FE80::AB8"
     19 237D                           # unsigned(9085)
     65                                # text(5)
         6964656E74                    # "ident"
     19 0119                           # unsigned(281)
     59 027F                           # bytes(639)
     <cacrts response payload>

In CBOR diagnostic:

    payload = [60, ["FE80::AB8", 9085, "ident"],
               62, h'<cacrts response payload>']

A.2. serverkeygen

The request from Join Proxy to EST-server looks like:

    Get coaps://
    (Accept: 62)
    (Content-Format: 62)
      Payload =
    83                                # array(4)
    18 3C                             # unsigned(60)
    83                                # array(3)
    69                                # text(9)
         464538303A3A414238           # "FE80::AB8"
    19 237D                           # unsigned(9085)
    65                                # text(5)
         6964656E74                   # "ident"
    19 011E                           # unsigned(286)
    58 D2                             # bytes(210)
    <serverkeygen request payload>

In CBOR diagnostic:

    payload = [60, ["FE80::AB8", 9085, "ident"],
               286, h'<serverkeygen request payload>']

The response will then be:

     2.05 Content
     (Content-format: 62)
       Payload =
     83                                # array(4)
     18 3C                             # unsigned(60)
     83                                # array(3)
     69                                # text(9)
         464538303A3A414238            # "FE80::AB8"
     19 237D                           # unsigned(9085)
     65                                # text(5)
         6964656E74                    # "ident"
     19 011E                           # unsigned(286)
     59 0269                           # bytes(617)
     <serverkeygen response payload>

In CBOR diagnostic:

    payload = [60, ["FE80::AB8", 9085, "ident"],
               286, h'<serverkeygen response payload>']

Authors' Addresses

Michael Richardson
Sandelman Software Works
Peter van der Stok
vanderstok consultancy
Panos Kampanakis
Cisco Systems