NETCONF Working Group K. Watsen Internet-Draft Watsen Networks Intended status: Standards Track April 29, 2019 Expires: October 31, 2019 YANG Data Model for Global Trust Anchors draft-ietf-netconf-trust-anchors-04 Abstract This document defines a YANG 1.1 data model for configuring global sets of X.509 certificates and SSH host-keys that can be referenced by other data models for trust. While the SSH host-keys are uniquely for the SSH protocol, the X.509 certificates may have multiple uses, including authenticating protocol peers and verifying signatures. Editorial Note (To be removed by RFC Editor) This draft contains many placeholder values that need to be replaced with finalized values at the time of publication. This note summarizes all of the substitutions that are needed. No other RFC Editor instructions are specified elsewhere in this document. Artwork in this document contains shorthand references to drafts in progress. Please apply the following replacements: o "XXXX" --> the assigned RFC value for this draft o "YYYY" --> the assigned RFC value for draft-ietf-netconf-crypto- types Artwork in this document contains placeholder values for the date of publication of this draft. Please apply the following replacement: o "2019-04-29" --> the publication date of this draft The following Appendix section is to be removed prior to publication: o Appendix A. Change Log 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 Watsen Expires October 31, 2019 [Page 1]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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 October 31, 2019. Copyright Notice Copyright (c) 2019 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.2. Tree Diagram Notation . . . . . . . . . . . . . . . . . . 3 2. The Trust Anchors Model . . . . . . . . . . . . . . . . . . . 3 2.1. Tree Diagram . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Example Usage . . . . . . . . . . . . . . . . . . . . . . 4 2.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 7 3. Security Considerations . . . . . . . . . . . . . . . . . . . 14 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 4.1. The IETF XML Registry . . . . . . . . . . . . . . . . . . 14 4.2. The YANG Module Names Registry . . . . . . . . . . . . . 15 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.1. Normative References . . . . . . . . . . . . . . . . . . 15 5.2. Informative References . . . . . . . . . . . . . . . . . 15 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 17 A.1. 00 to 01 . . . . . . . . . . . . . . . . . . . . . . . . 17 A.2. 01 to 02 . . . . . . . . . . . . . . . . . . . . . . . . 17 A.3. 02 to 03 . . . . . . . . . . . . . . . . . . . . . . . . 17 A.4. 03 to 04 . . . . . . . . . . . . . . . . . . . . . . . . 17 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 17 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17 Watsen Expires October 31, 2019 [Page 2]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 1. Introduction This document defines a YANG 1.1 [RFC7950] data model for configuring global sets of X.509 certificates and SSH host-keys that can be referenced by other data models for trust. While the SSH host-keys are uniquely for the SSH protocol, the X.509 certificates may be used for multiple uses, including authenticating protocol peers and verifying signatures. This document in compliant with Network Management Datastore Architecture (NMDA) [RFC8342]. For instance, to support trust anchors installed during manufacturing, it is expected that such data may appear only in <operational>. 1.1. 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. 1.2. Tree Diagram Notation Tree diagrams used in this document follow the notation defined in [RFC8340]. 2. The Trust Anchors Model 2.1. Tree Diagram The following tree diagram provides an overview of the "ietf-trust- anchors" module. Watsen Expires October 31, 2019 [Page 3]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 module: ietf-trust-anchors +--rw trust-anchors +--rw pinned-certificates* [name] {x509-certificates}? | +--rw name string | +--rw description? string | +--rw pinned-certificate* [name] | +--rw name string | +--rw cert trust-anchor-cert-cms | +---n certificate-expiration | +-- expiration-date yang:date-and-time +--rw pinned-host-keys* [name] {ssh-host-keys}? +--rw name string +--rw description? string +--rw pinned-host-key* [name] +--rw name string +--rw host-key ct:ssh-host-key grouping local-or-truststore-certs-grouping +-- (local-or-truststore) +--:(local) {local-trust-anchors-supported}? | +-- local-definition | +-- cert* trust-anchor-cert-cms | +---n certificate-expiration | +-- expiration-date yang:date-and-time +--:(truststore) {truststore-supported}? +-- truststore-reference? ta:pinned-certificates-ref grouping local-or-truststore-host-keys-grouping +-- (local-or-truststore) +--:(local) {local-trust-anchors-supported}? | +-- local-definition | +-- host-key* ct:ssh-host-key | +-- cert* trust-anchor-cert-cms | +---n certificate-expiration | +-- expiration-date yang:date-and-time +--:(truststore) {truststore-supported}? +-- truststore-reference? ta:pinned-host-keys-ref 2.2. Example Usage The following example illustrates trust anchors in <operational> as described by Section 5.3 in [RFC8342]. This datastore view illustrates data set by the manufacturing process alongside conventional configuration. This trust anchors instance has six sets of pinned certificates and one set of pinned host keys. <trust-anchors xmlns="urn:ietf:params:xml:ns:yang:ietf-trust-anchors" xmlns:or="urn:ietf:params:xml:ns:yang:ietf-origin"> Watsen Expires October 31, 2019 [Page 4]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 <!-- Manufacturer's trusted root CA certs --> <pinned-certificates or:origin="or:system"> <name>manufacturers-root-ca-certs</name> <description> Certificates built into the device for authenticating manufacturer-signed objects, such as TLS server certificates, vouchers, etc. Note, though listed here, these are not configurable; any attempt to do so will be denied. </description> <pinned-certificate> <name>Manufacturer Root CA cert 1</name> <cert>base64encodedvalue==</cert> </pinned-certificate> <pinned-certificate> <name>Manufacturer Root CA cert 2</name> <cert>base64encodedvalue==</cert> </pinned-certificate> </pinned-certificates> <!-- specific end-entity certs for authenticating servers --> <pinned-certificates or:origin="or:intended"> <name>explicitly-trusted-server-certs</name> <description> Specific server authentication certificates for explicitly trusted servers. These are needed for server certificates that are not signed by a pinned CA. </description> <pinned-certificate> <name>Fred Flintstone</name> <cert>base64encodedvalue==</cert> </pinned-certificate> </pinned-certificates> <!-- trusted CA certs for authenticating servers --> <pinned-certificates or:origin="or:intended"> <name>explicitly-trusted-server-ca-certs</name> <description> Trust anchors (i.e. CA certs) that are used to authenticate server connections. Servers are authenticated if their certificate has a chain of trust to one of these CA certificates. </description> <pinned-certificate> <name>ca.example.com</name> <cert>base64encodedvalue==</cert> </pinned-certificate> </pinned-certificates> Watsen Expires October 31, 2019 [Page 5]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 <!-- specific end-entity certs for authenticating clients --> <pinned-certificates or:origin="or:intended"> <name>explicitly-trusted-client-certs</name> <description> Specific client authentication certificates for explicitly trusted clients. These are needed for client certificates that are not signed by a pinned CA. </description> <pinned-certificate> <name>George Jetson</name> <cert>base64encodedvalue==</cert> </pinned-certificate> </pinned-certificates> <!-- trusted CA certs for authenticating clients --> <pinned-certificates or:origin="or:intended"> <name>explicitly-trusted-client-ca-certs</name> <description> Trust anchors (i.e. CA certs) that are used to authenticate client connections. Clients are authenticated if their certificate has a chain of trust to one of these CA certificates. </description> <pinned-certificate> <name>ca.example.com</name> <cert>base64encodedvalue==</cert> </pinned-certificate> </pinned-certificates> <!-- trusted CA certs for random HTTPS servers on Internet --> <pinned-certificates or:origin="or:system"> <name>common-ca-certs</name> <description> Trusted certificates to authenticate common HTTPS servers. These certificates are similar to those that might be shipped with a web browser. </description> <pinned-certificate> <name>ex-certificate-authority</name> <cert>base64encodedvalue==</cert> </pinned-certificate> </pinned-certificates> <!-- specific SSH host keys for authenticating clients --> <pinned-host-keys or:origin="or:intended"> <name>explicitly-trusted-ssh-host-keys</name> <description> Trusted SSH host keys used to authenticate SSH servers. Watsen Expires October 31, 2019 [Page 6]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 These host keys would be analogous to those stored in a known_hosts file in OpenSSH. </description> <pinned-host-key> <name>corp-fw1</name> <host-key>base64encodedvalue==</host-key> </pinned-host-key> </pinned-host-keys> </trust-anchors> The following example illustrates the "certificate-expiration" notification in use with the NETCONF protocol. =========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) =========== <notification xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0"> <eventTime>2018-05-25T00:01:00Z</eventTime> <trust-anchors xmlns="urn:ietf:params:xml:ns:yang:ietf-trust-anchors"> <pinned-certificates> <name>explicitly-trusted-client-certs</name> <pinned-certificate> <name>George Jetson</name> <certificate-expiration> <expiration-date>2018-08-05T14:18:53-05:00</expiration-dat\ e> </certificate-expiration> </pinned-certificate> </pinned-certificates> </trust-anchors> </notification> 2.3. YANG Module This YANG module imports modules from [RFC8341] and [I-D.ietf-netconf-crypto-types]. <CODE BEGINS> file "ietf-trust-anchors@2019-04-29.yang" module ietf-trust-anchors { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-trust-anchors"; prefix ta; import ietf-netconf-acm { prefix nacm; Watsen Expires October 31, 2019 [Page 7]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 reference "RFC 8341: Network Configuration Access Control Model"; } import ietf-crypto-types { prefix ct; reference "RFC YYYY: Common YANG Data Types for Cryptography"; } organization "IETF NETCONF (Network Configuration) Working Group"; contact "WG Web: <http://datatracker.ietf.org/wg/netconf/> WG List: <mailto:netconf@ietf.org> Author: Kent Watsen <mailto:kent+ietf@watsen.net>"; description "This module defines a data model for configuring global trust anchors used by other data models. The data model enables the configuration of sets of trust anchors. This data model supports configuring trust anchors for both X.509 certificates and SSH host keys. Copyright (c) 2019 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices.; 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 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here."; revision 2019-04-29 { description Watsen Expires October 31, 2019 [Page 8]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 "Initial version"; reference "RFC XXXX: YANG Data Model for Global Trust Anchors"; } /****************/ /* Features */ /****************/ feature truststore-supported { description "The 'truststore-supported' feature indicates that the server supports the truststore."; } feature local-trust-anchors-supported { description "The 'local-keys-supported' feature indicates that the server supports locally-defined trust anchors."; } feature x509-certificates { description "The 'x509-certificates' feature indicates that the server implements the /trust-anchors/pinned-certificates subtree."; } feature ssh-host-keys { description "The 'ssh-host-keys' feature indicates that the server implements the /trust-anchors/pinned-host-keys subtree."; } /****************/ /* Typedefs */ /****************/ typedef pinned-certificates-ref { type leafref { path "/ta:trust-anchors/ta:pinned-certificates/ta:name"; require-instance false; // IS THIS STILL TRUE? // - doesn't the client now create a 'config' instance? // - they do in order to config a new cert (e.g., LDevID) } description "This typedef enables importing modules to easily define a leafref to a 'pinned-certificates' object. The 'require- instance' attribute is 'false' to enable the referencing Watsen Expires October 31, 2019 [Page 9]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 of pinned certificates that exist only in <operational>."; reference "RFC 8342: Network Management Datastore Architecture (NMDA)"; } typedef pinned-host-keys-ref { type leafref { path "/ta:trust-anchors/ta:pinned-host-keys/ta:name"; require-instance false; // IS THIS STILL TRUE? // - doesn't the client now create a 'config' instance? // - they do in order to config a new cert (e.g., LDevID) } description "This typedef enables importing modules to easily define a leafref to a 'pinned-host-keys' object. The 'require- instance' attribute is 'false' to enable the referencing of pinned host keys that exist only in <operational>."; reference "RFC 8342: Network Management Datastore Architecture (NMDA)"; } /*****************/ /* Groupings */ /*****************/ grouping local-or-truststore-certs-grouping { description "A grouping that expands to allow trust anchors to be either stored locally, within the using data model, or be a reference to trust anchors stored in the truststore."; choice local-or-truststore { mandatory true; case local { if-feature "local-trust-anchors-supported"; container local-definition { description "Container to hold the local trust anchor definitions. A list is defined so as to be symmetric with the truststore definition."; uses ct:trust-anchor-certs-grouping; } } case truststore { if-feature "truststore-supported"; leaf truststore-reference { type ta:pinned-certificates-ref; description "A reference to a trust anchor that exists in the Watsen Expires October 31, 2019 [Page 10]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 truststore."; } } description "A choice between an inlined definition and a definition that exists in the truststore."; } } grouping local-or-truststore-host-keys-grouping { description "A grouping that expands to allow trust anchors to be either stored locally, within the using data model, or be a reference to trust anchors stored in the truststore."; choice local-or-truststore { mandatory true; case local { if-feature "local-trust-anchors-supported"; container local-definition { description "Container to hold the local trust anchor definitions. A list is defined so as to be symmetric with the truststore definition."; leaf-list host-key { nacm:default-deny-write; type ct:ssh-host-key; description "The binary data for this host key."; reference "RFC YYYY: Common YANG Data Types for Cryptography"; } uses ct:trust-anchor-certs-grouping; } } case truststore { if-feature "truststore-supported"; leaf truststore-reference { type ta:pinned-host-keys-ref; description "A reference to a trust anchor that exists in the truststore."; } } description "A choice between an inlined definition and a definition that exists in the truststore."; } } Watsen Expires October 31, 2019 [Page 11]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 /*********************************/ /* Protocol accessible nodes */ /*********************************/ container trust-anchors { nacm:default-deny-write; description "Contains sets of X.509 certificates and SSH host keys."; list pinned-certificates { if-feature "x509-certificates"; key "name"; description "A list of pinned certificates. These certificates can be used by a server to authenticate clients, or by a client to authenticate servers. Each list of pinned certificates SHOULD be specific to a purpose, as the list as a whole may be referenced by other modules. For instance, a RESTCONF server's configuration might use a specific list of pinned certificates for when authenticating RESTCONF client connections."; leaf name { type string; description "An arbitrary name for this list of pinned certificates."; } leaf description { type string; description "An arbitrary description for this list of pinned certificates."; } list pinned-certificate { key "name"; description "A pinned certificate."; leaf name { type string; description "An arbitrary name for this pinned certificate. The name must be unique across all lists of pinned certificates (not just this list) so that leafrefs from another module can resolve to unique values."; } uses ct:trust-anchor-cert-grouping { refine "cert" { mandatory true; } } Watsen Expires October 31, 2019 [Page 12]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 } } list pinned-host-keys { if-feature "ssh-host-keys"; key "name"; description "A list of pinned host keys. These pinned host-keys can be used by clients to authenticate SSH servers. Each list of pinned host keys SHOULD be specific to a purpose, so the list as a whole may be referenced by other modules. For instance, a NETCONF client's configuration might point to a specific list of pinned host keys for when authenticating specific SSH servers."; leaf name { type string; description "An arbitrary name for this list of pinned SSH host keys."; } leaf description { type string; description "An arbitrary description for this list of pinned SSH host keys."; } list pinned-host-key { key "name"; description "A pinned host key."; leaf name { type string; description "An arbitrary name for this pinned host-key. Must be unique across all lists of pinned host-keys (not just this list) so that a leafref to it from another module can resolve to unique values."; } leaf host-key { type ct:ssh-host-key; mandatory true; description "The binary public key data for this pinned host key."; reference "RFC YYYY: Common YANG Data Types for Cryptography"; } } } } Watsen Expires October 31, 2019 [Page 13]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 } <CODE ENDS> 3. Security Considerations The YANG module defined in this document is designed to be accessed via YANG based management protocols, such as NETCONF [RFC6241] and RESTCONF [RFC8040]. Both of these protocols have mandatory-to- implement secure transport layers (e.g., SSH, TLS) with mutual authentication. The NETCONF access control model (NACM) [RFC8341] provides the means to restrict access for particular users to a pre-configured subset of all available protocol operations and content. There are a number of data nodes defined in this YANG module that are writable/creatable/deletable (i.e., config true, which is the default). These data nodes may be considered sensitive or vulnerable in some network environments. Write operations (e.g., edit-config) to these data nodes without proper protection can have a negative effect on network operations. These are the subtrees and data nodes and their sensitivity/vulnerability: /: The entire data tree defined by this module is sensitive to write operations. For instance, the addition or removal of any trust anchor may dramatically alter the implemented security policy. For this reason, the NACM extension "default-deny- write" has been set for the entire data tree. None of the readable data nodes in this YANG module are considered sensitive or vulnerable in network environments. This module does not define any RPCs, actions, or notifications, and thus the security consideration for such is not provided here. 4. IANA Considerations 4.1. The IETF XML Registry This document registers one URI in the "ns" subregistry of the IETF XML Registry [RFC3688]. Following the format in [RFC3688], the following registration is requested: URI: urn:ietf:params:xml:ns:yang:ietf-trust-anchors Registrant Contact: The NETCONF WG of the IETF. XML: N/A, the requested URI is an XML namespace. Watsen Expires October 31, 2019 [Page 14]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 4.2. The YANG Module Names Registry This document registers one YANG module in the YANG Module Names registry [RFC6020]. Following the format in [RFC6020], the the following registration is requested: name: ietf-trust-anchors namespace: urn:ietf:params:xml:ns:yang:ietf-trust-anchors prefix: ta reference: RFC XXXX 5. References 5.1. Normative References [I-D.ietf-netconf-crypto-types] Watsen, K. and H. Wang, "Common YANG Data Types for Cryptography", draft-ietf-netconf-crypto-types-05 (work in progress), March 2019. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, <https://www.rfc-editor.org/info/rfc7950>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>. [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018, <https://www.rfc-editor.org/info/rfc8341>. 5.2. Informative References [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, <https://www.rfc-editor.org/info/rfc3688>. Watsen Expires October 31, 2019 [Page 15]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, <https://www.rfc-editor.org/info/rfc6020>. [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, <https://www.rfc-editor.org/info/rfc6241>. [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, <https://www.rfc-editor.org/info/rfc8040>. [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, <https://www.rfc-editor.org/info/rfc8340>. [RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018, <https://www.rfc-editor.org/info/rfc8342>. Watsen Expires October 31, 2019 [Page 16]
Internet-Draft YANG Data Model for Global Trust Anchors April 2019 Appendix A. Change Log A.1. 00 to 01 o Added features "x509-certificates" and "ssh-host-keys". o Added nacm:default-deny-write to "trust-anchors" container. A.2. 01 to 02 o Switched "list pinned-certificate" to use the "trust-anchor-cert- grouping" from crypto-types. Effectively the same definition as before. A.3. 02 to 03 o Updated copyright date, boilerplate template, affiliation, folding algorithm, and reformatted the YANG module. A.4. 03 to 04 o Added groupings 'local-or-truststore-certs-grouping' and 'local- or-truststore-host-keys-grouping', matching similar definitions in the keystore draft. Note new (and incomplete) "truststore" usage! o Related to above, also added features 'truststore-supported' and 'local-trust-anchors-supported'. Acknowledgements The authors would like to thank for following for lively discussions on list and in the halls (ordered by last name): Martin Bjorklund, Balazs Kovacs, Eric Voit, and Liang Xia. Author's Address Kent Watsen Watsen Networks EMail: kent+ietf@watsen.net Watsen Expires October 31, 2019 [Page 17]