Looking Glass Command Set
RFC 8522

Independent Submission                                        M. Stubbig
Request for Comments: 8522                                   Independent
Category: Informational                                    February 2019
ISSN: 2070-1721

                       Looking Glass Command Set

Abstract

   This document introduces a command set standard to the web-based
   "Network Looking Glass" software.  Its purpose is to provide
   application programmers uniform access to the Looking Glass service
   and to analyze a standardized response.

   The interface is supposed to provide the same level of information as
   web-based interfaces, but in a computer-readable format.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not candidates for any level of Internet Standard;
   see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8522.

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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Background  . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Syntax Notation . . . . . . . . . . . . . . . . . . . . .   3
     1.3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Method Parameters . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Query Parameters  . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Response  . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Functions . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     3.1.  Diagnostic Commands . . . . . . . . . . . . . . . . . . .   9
     3.2.  Informational Commands  . . . . . . . . . . . . . . . . .  10
     3.3.  Organizational Commands . . . . . . . . . . . . . . . . .  14
     3.4.  Extensible Commands . . . . . . . . . . . . . . . . . . .  16
   4.  Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . .  16
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     5.1.  Well-Known URIs Registry  . . . . . . . . . . . . . . . .  17
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
     6.1.  Abuse Potential . . . . . . . . . . . . . . . . . . . . .  17
     6.2.  Authentication  . . . . . . . . . . . . . . . . . . . . .  17
     6.3.  Minimal Information . . . . . . . . . . . . . . . . . . .  17
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  18
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Appendix A.  JSend  . . . . . . . . . . . . . . . . . . . . . . .  20
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   Many Internet service providers (ISPs) and Internet exchange points
   (IXPs) offer a complimentary web-based service to their customers and
   the general public that gives insights to the backbone routing table,
   BGP neighbor information, or offered routes.  This service is known
   as a "Network Looking Glass".  Because they utilize a web-based
   interface, it is hard to automate access to the services and make
   that automation transferable between different service
   implementations.

   This document describes a common command set to provide application
   programmers uniform access to Looking Glass services.

   The commands are intended to provide the same level of information as
   available via web-based interfaces, but to do so in a computer-
   readable format.  The intention is that multiple implementers of
   Looking Glass services can provide access through these commands so
   that an application can make use of the different implementations.

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   The command set is split into the following categories: mandatory to
   support, optional, and additional.  The commands are extensible for
   new features and for value-add by implementations.

   The Looking Glass command set is described as a language-independent
   concept.  Consequently, any programming language that satisfies the
   commands listed in the following sections is acceptable.

   This work is not the output of the IETF and is presented in the hope
   that Looking Glass implementers will offer a common programmable
   interface.

1.1.  Background

   The requirement of a uniform access to a Looking Glass service
   becomes important when multiple Looking Glasses are part of a
   monitoring system.  Implementing a web client and HTTP parser for
   every kind of web-based Looking Glass is a time-consuming workaround.
   However, the Looking Glass command set is a much more viable,
   compatible, and scalable solution.

1.2.  Syntax Notation

   This specification uses the JavaScript Object Notation (JSON) of
   [RFC8259] arranged as JSend-compliant (Appendix A) responses.

1.3.  Examples

   All URLs in this documentation use the reserved sample domain of
   "example.net" as defined in Section 6.5 of [RFC6761].

   The URLs further use the fixed [RFC5785] prefix of ".well-known/
   looking-glass" to prevent a collision in the domain's namespace.

   IPv4 addresses use the documentation block of 192.0.2.0/24 [RFC5737]
   and IPv6 addresses reside in the reserved prefix of 2001:DB8::/32
   [RFC3849].  BGP Autonomous System (AS) numbers are chosen from the
   private AS range defined in [RFC6996].

   The examples skip some required parameters for reasons of simplicity.

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2.  Operation

   A client issues a query using the HTTP GET method to request specific
   resources from the server.  The resource is a URI and can be
   informational or a command execution.  The client must present all
   necessary parameters for the server to execute the command on the
   selected router.  Every call is stateless and independent of the
   previous one.

   The path component of the resource URI must use the prefix of ".well-
   known/looking-glass" (see Section 5.1) to stay namespace neutral.

   The "call" is a request from the client that specifies a predefined
   operation ("function") that the server will execute on a selected
   router.  The "command" is a task executed on the router and initiated
   by the server on behalf of the client.  The type and scope of all
   commands are defined and limited by the server.  The client must not
   be able to execute random commands on the targeting router.  There
   must not be any direct communication between the client and the
   router.

   After the execution of the command on the selected router has
   finished, the server replies to the client if the operation has
   either succeeded, failed, or timed out.  The response is sent to the
   client in JSON format.  The communication protocol used between the
   server and router is not specified by this document; any method
   (e.g., Telnet, SSH, NETCONF, serial console) is acceptable.

   All parameters and their values are case insensitive.

2.1.  Method Parameters

   Method parameters are mandatory components of the URI and are placed
   in the "path" section in terms of [RFC7320].  Basically, the method
   parameters specify the call and determine which command the client
   wants to be executed on the selected router.

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2.2.  Query Parameters

   Query parameters are optional components of the URI and are placed in
   the "query" section in terms of [RFC7320].  Generally, the query
   parameters are additional instructions for the requested command.

   protocol
      Restrict the command and method parameters to use the specified
      protocol and version.  Protocol is selected as "Address Family
      Identifier" [IANA-AFN] [RFC4760] and optionally as "Subsequent
      Address Family Identifier" [IANA-SAFI] separated by a comma.
      Default value is 1,1 (IP version 4, unicast).
      JSON datatype is String.
      Examples:

      *  protocol=2,1 (IP version 6, unicast)

      *  protocol=26 (MPLS, no SAFI used)

   router
      Run the command on the router identified by its name.  This is not
      necessarily the router's hostname as long as the Looking Glass
      software recognizes it.
      Default value is the first router in the list of available
      routers.
      JSON datatype is String.
      Example: router=rbgn06.example.net

   routerindex
      Run the command on this router identified by its position in the
      list of available routers.
      Default value is "0".
      JSON datatype is Number.
      Example: routerindex=8

   random
      Append a random string to prevent the client (or an intermediate
      proxy) from caching the response.  The server must ignore its
      value.
      No default value.
      JSON datatype is String.
      Example: random=517A93B50

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   vrf
      Run the command from the selected routing table.  This parameter
      is valid only on routers that support "Virtual Routing and
      Forwarding" (VRF).
      No default value.
      JSON datatype is String.
      Example: vrf=mgmt

   runtime
      Stop executing the command after the runtime limit (in seconds) is
      exceeded.  A value of 0 disables the limit.
      Default value is "30".
      JSON datatype is Number.
      Example: runtime=60

   format
      Request the server to provide the output (if any) in the selected
      format.  Specify multiple formats separated by a comma in
      descending order of preference.  See Section 3.3.2 for more
      details.
      Default value is "text/plain" (raw/unformatted output).
      JSON datatype is String.
      Example: format=application/yang,text/plain

2.3.  Response

   The HTTP response header contains an appropriate HTTP status code as
   defined in [RFC7231] with the Content-Type set to "application/json".

   The HTTP body contains details and error descriptions.  The response
   text must comply with the JSON syntax specification JSend, which is
   briefly explained in Appendix A.  Consequently, every response must
   contain a "status" field of either "success", "fail", or "error" as
   explained in the following sections.

2.3.1.  Success

   A successful response must set the "status" field to "success".  It
   must also contain a "data" object including the following
   information:

   performed_at
      Combined date and time in UTC ISO 8601 [iso8601] indicating when
      the operation finished.  This information must be present.

   runtime
      Amount of seconds (wallclock) used to run the command.  This
      information must be present.

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   router
      Name of the router that executed the command.  This information
      may be present.

   output
      Output of the command in a format that was requested by the
      client; it otherwise defaults to raw output as it appeared on the
      router's command-line interface (CLI).  It might even be blank if
      the command did not produce any output.  This information should
      be present.

   format
      Selected output format by the server.  The client might request
      multiple formats so that the "Looking Glass" server has to choose
      the best option and tell the client which format was selected.
      This information should be present (defaults to "text/plain" if
      missing).

   Adding more information to the response is permitted and must be
   placed inside the "data" object.

   The HTTP status code should be 200.

   Example:

   HTTP/1.1 200 OK
   Content-Type: application/json
   {
     "status" : "success",
     "data" : {
       "router" : "route-server.lookingglass.example.net"
       "performed_at" : "2014-10-15T17:15:34Z",
       "runtime" : 2.63,
       "output" : [
         "full raw output from the observing router..."
       ],
       "format" : "text/plain"
     }
   }

2.3.2.  Fail

   A status of "fail" indicates that the selected command was executed
   on the router but failed to succeed.  The response message must set
   the "status" field to "fail" and must contain the "data" object with
   command-specific content listed in Section 2.3.1.

   The HTTP status code should be 200.

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   Example:

   HTTP/2.0 200 OK
   {
     "status" : "fail",
     "data" : {
       "performed_at" : "2014-10-18T20:04:37Z",
       "runtime" : 10.37,
       "output" : [
         "Sending 5, 100-byte ICMP Echos to 192.0.2.5",
         ".....",
         "Success rate is 0 percent (0/5)"
       ],
       "format" : "text/plain",
       "router" : "route-server.lookingglass.example.net"
     }
   }

2.3.3.  Error

   The status "error" represents either that the command timed out or
   that an error occurred in processing the request.  The response
   message must set the "status" field to "error" and must contain the
   "message" key, which keeps a meaningful message, explaining what went
   wrong.

   The response may contain the "data" key with required values listed
   in Section 2.3.1.  It may also include a "code" field that carries a
   numeric code corresponding to the error.

   The HTTP status code should be 400 in case of a client-side error,
   500 in case of a server-side error, or 502 for errors occurring on
   the target router.  Code 504 should be used when a command timed out.

   Example:

   HTTP/1.1 400 Bad Request
   {
     "status" : "error",
     "message" : "Unrecognized host or address."
   }

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3.  Functions

   The Looking Glass command set provides functions that are either
   mandatory to support or optional to implement.  The same principle
   applies to the web-based Looking Glass.

   It is not possible for any function to modify the server's state.
   Therefore, all HTTP methods are GET operations.

   Variables are templated and expanded in accordance with [RFC6570].

3.1.  Diagnostic Commands

3.1.1.  Ping

   Send echo messages to validate the reachability of a remote host and
   measure round-trip time.  The host can be a name or address.

   Implementation of the ping command is mandatory.

   Syntax: https://example.net/.well-known/looking-glass/v1/ping/{host}

   Example query:

   GET /.well-known/looking-glass/v1/ping/2001:DB8::35?protocol=2,1
   Host: example.net

   Example response:

   HTTP/1.1 200 OK
   {
     "status" : "success",
     "data" : {
       "min" : 40,
       "avg" : 41,
       "max" : 44,
       "rate" : 100,
       "output" : [
         "Sending 5, 100-byte ICMP Echos to 2001:DB8::35",
         "!!!!!",
         "Success rate is 100 percent (5/5)"
       ],
       "format" : "text/plain",
       "performed_at" : "2014-10-04T14:40:58Z",
       "runtime" : 0.77,
       "router" : "c2951.lab.lg.example.net"
     }
   }

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3.1.2.  Traceroute

   Trace the path from the executing router to the destination host and
   list all intermediate hops.  The host can be a name or address.

   Implementation of the traceroute command is optional.

   Syntax: https://example.net/.well-known/looking-glass/v1/
   traceroute/{host}

   Example query:

   GET /.well-known/looking-glass/v1/traceroute/192.0.2.8?routerindex=5
   Host: example.net

   Example response:

   HTTP/1.1 200 OK
   {
     "status": "success",
     "data": {
       "output": [
         "Tracing the route to 192.0.2.8",
         "",
         "  1 198.51.100.77 28 msec 28 msec 20 msec",
         "  2 203.0.113.130 52 msec 40 msec 40 msec",
         "  3 192.0.2.8 72 msec 76 msec 68 msec"
       ],
       "format": "text/plain",
       "performed_at": "2018-06-10T12:09:31Z",
       "runtime": 4.21,
       "router": "c7206.lab.lg.example.net"
     }
   }

3.2.  Informational Commands

3.2.1.  show route

   Retrieve information about a specific subnet from the routing table.

   Implementation of the "show route" command is mandatory.

   Syntax: https://example.net/.well-known/looking-glass/v1/show/
   route/{addr}

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   Example query:

   GET /.well-known/looking-glass/v1/show/      [multiline]
           route/2001:DB8::/48?protocol=2,1
   Host: example.net

   Example response:

   HTTP/1.1 200 OK
   {
     "status": "success",
     "data": {
       "output": [
         "S   2001:DB8::/48 [1/0]",
         "     via FE80::C007:CFF:FED9:17, FastEthernet0/0"
       ],
       "format": "text/plain",
       "performed_at": "2018-06-11T17:13:39Z",
       "runtime": 1.39,
       "router": "c2951.lab.lg.example.net"
     }
   }

3.2.2.  show bgp

   Display a matching record from the BGP routing table.  This should
   include networks, next hop, and may include metric, local preference,
   path list, weight, etc.

   Implementation of the "show bgp" command is optional.

   Syntax: https://example.net/.well-known/looking-glass/v1/show/
   bgp/{addr}

   Example query:

   GET /.well-known/looking-glass/v1/show/bgp/192.0.2.0/24
   Host: example.net

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   Example response:

   HTTP/1.1 200 OK
   {
     "status": "success",
     "data": {
       "output": [
         "BGP routing table entry for 192.0.2.0/24, version 2",
         "Paths: (2 available, best #2, table default)",
         "  Advertised to update-groups:",
         "     1",
         "  Refresh Epoch 1",
         "  Local",
         "    192.0.2.226 from 192.0.2.226 (192.0.2.226)",
         "      Origin IGP, metric 0, localpref 100, valid, internal",
         "[...]"
       ],
       "format": "text/plain",
       "performed_at": "2018-06-11T21:47:17Z",
       "runtime": 2.03,
       "router": "c2951.lab.lg.example.net"
     }
   }

3.2.3.  show bgp summary

   Print a summary of BGP neighbor status.  This may include the
   neighbor BGP ID, autonomous system number, duration of peering,
   number of received prefixes, etc.

   Implementation of the "show bgp summary" command is optional.

   Syntax: https://example.net/.well-known/looking-glass/v1/show/bgp/
   summary

   Example:

   GET /.well-known/looking-glass/v1/show/bgp/summary?     [multiline]
          protocol=2&routerindex=3
   Host: example.net

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   Example response:

   HTTP/1.1 200 OK
   {
     "status": "success",
     "data": {
       "output": [
         "BGP router identifier 192.0.2.18, local AS number 64501",
         "BGP table version is 85298, main routing table version 85298",
         "50440 network entries using 867568 bytes of memory",
         "[...]",
         "Neighbor        V       AS MsgRcvd MsgSent   TblVer  Up/Down",
         "2001:DB8:91::24 4    64500  481098  919095   85298   41w5d"
       ],
       "format": "text/plain",
       "performed_at": "2018-06-11T21:59:21Z",
       "runtime": 1.91,
       "router": "c2951.lab.lg.example.net"
     }
   }

3.2.4.  show bgp neighbors

   Provide detailed information on BGP neighbor connections.  Available
   details may include neighbor BGP ID, advertised networks, learned
   networks, autonomous system number, capabilities, protocol,
   statistics, etc.

   Implementation of the "show bgp neighbors" command is optional.

   Syntax: https://example.net/.well-known/looking-glass/v1/show/bgp/
   neighbors/{addr}

   Example query:

   GET /.well-known/looking-glass/v1/show/bgp/neighbors/192.0.2.226
   Host: example.net

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   Example response:

   HTTP/1.1 200 OK
   {
     "status": "success",
     "data": {
       "output": [
         "BGP neighbor is 192.0.2.226, remote AS 64500, internal link",
         "  BGP version 4, remote router ID 198.51.100.31",
         "  BGP state = Established, up for 01:24:06",
         "[...]"
       ],
       "format": "text/plain",
       "performed_at": "2018-06-11T21:41:17Z",
       "runtime": 1.87,
       "router": "c2951.lab.lg.example.net"
     }
   }

3.3.  Organizational Commands

   The following organizational commands must be included in the
   implementation.

3.3.1.  router list

   Provides a full list of routers that are available for command
   execution.  This list includes the router ID and its name.  It is
   equivalent to the common "router" HTML drop-down form element and
   contains the same information.

   Syntax: https://example.net/.well-known/looking-glass/v1/routers

   Example response:

   {
     "status" : "success",
     "data" : {
       "routers" : [
         "route-server.lookingglass.example.net",
         "customer-edge.lookingglass.example.net",
         "provider-edge.lookingglass.example.net"
       ],
       "performed_at" : "2014-10-19T20:07:01Z",
       "runtime" : 0.73
     }
   }

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3.3.2.  router details

   Lists additional information about the selected router specified by
   its router index.  The response must contain the router's hostname
   and router index.  The response may contain more details like output
   format, country code, city, administrative contact, vendor, and
   model.

   Available output formats are specified by Internet media type as of
   [RFC6838] and listed in [IANA-MT].  If the routers support multiple
   formats, they are separated by a comma.

   The router might provide output formats that are not yet registered
   or listed in [IANA-MT].  For example, output in NETCONF format could
   use "text/x.netconf".  [RFC6838] provides a tree for unregistered
   subtypes.

   A missing output format defaults to "text/plain", which is a copy of
   the raw command-line output.

   Syntax: https://example.net/.well-known/looking-glass/v1/
   routers/{number}

   Example query:

   GET /.well-known/looking-glass/v1/routers/1
   Host: example.net

   Example response:

   {
     "status" : "success",
     "data" : {
       "id" : 1,
       "name" : "customer-edge.lookingglass.example.net",
       "format" : "text/plain,text/x.netconf",
       "country" : "de",
       "autonomous_system" : 64512
     }
   }

3.3.3.  commands

   Provides a full list of commands that are available for execution.
   The list includes mandatory to support, optional, and additional
   (Section 3.4) commands.  It is equivalent to the "command" HTML drop-
   down or radio-button form element and contains the same information.

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   The list is formatted as a "commands" array containing one object per
   command.  This object contains informative strings about the current
   command: href, arguments, description, and command.

   Syntax: https://example.net/.well-known/looking-glass/v1/cmd

   Example response:

   {
     "status" : "success",
     "data" : {
       "commands" : [
         {
           "href" : "https://example.net/.well-known/     [multiline]
                             looking-glass/v1/show/route",
           "arguments" : "{addr}",
           "description" : "Print records from IP routing table",
           "command" : "show route"
         },
         {
           "href" : "https://example.net/.well-known/     [multiline]
                             looking-glass/v1/traceroute",
           "arguments" : "{addr}",
           "description" : "Trace route to destination host",
           "command" : "traceroute"
         }
       ]
     }
   }

3.4.  Extensible Commands

   The list of commands discussed in Section 3.3.3 may be expanded as
   long as the principles of this document are observed.

   For example, a Looking Glass provider may not be offering BGP-related
   commands because of an OSPF-based network.

   The sample command might be:

   GET /.well-known/looking-glass/v1/show/ospf/database
   Host: example.net

4.  Miscellaneous

   The network traffic sent by a "Looking Glass" is not appropriate when
   measuring Service Level Agreements or validating Quality of Service
   settings.

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   If a monitoring system uses the Looking Glass command set for
   reachability checks, it should not rely on the HTTP status codes but
   on the "status" message field inside the HTTP body.

5.  IANA Considerations

5.1.  Well-Known URIs Registry

   This specification registers a Well-Known URI [RFC5785]:

   URI Suffix: looking-glass

   Change Controller: M. Stubbig

   Reference : This document, Section 2

6.  Security Considerations

   The use of HTTPS is required to ensure a high level of security,
   privacy, and confidentiality during transit.

6.1.  Abuse Potential

   The main goal of the Looking Glass command set is the automated usage
   of the Looking Glass service.  This allows the scripting of API
   calls, which could be used as a Distributed Denial of Service (DDoS)
   attack.  It is recommended that implementers of the Looking Glass API
   take steps to mitigate the above described abuse.  The strategy can
   include blocking or rate-limiting by client IP address or target IP
   network.

6.2.  Authentication

   Authentication is not a requirement because the current Looking Glass
   web services are usable without authentication.  Requests to the
   proposed API service may be authenticated by any method.  The
   decision is up to the implementer's security requirements.

6.3.  Minimal Information

   Some of the described commands provide a detailed insight into the
   provider's network.  It is therefore up to the implementer's security
   policy to dismiss commands that are marked as "optional" or to
   restrict commands that are marked as "mandatory".

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7.  References

7.1.  Normative References

   [IANA-AFN] IANA, "Address Family Numbers", <https://www.iana.org/
              assignments/address-family-numbers/>.

   [IANA-MT]  IANA, "Media Types",
              <https://www.iana.org/assignments/media-types/>.

   [IANA-SAFI]
              IANA, "Subsequent Address Family Identifiers (SAFI)
              Parameters",
              <https://www.iana.org/assignments/safi-namespace/>.

   [JSend]    OmniTI Labs, "JSend", 2014,
              <https://labs.omniti.com/labs/jsend>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              DOI 10.17487/RFC5785, April 2010,
              <https://www.rfc-editor.org/info/rfc5785>.

   [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", RFC 6570,
              DOI 10.17487/RFC6570, March 2012,
              <https://www.rfc-editor.org/info/rfc6570>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

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7.2.  Informative References

   [iso8601]  International Organization for Standardization, "Data
              elements and interchange formats - Information interchange
              - Representation of dates and times", December 2004.

   [RFC3849]  Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix
              Reserved for Documentation", RFC 3849,
              DOI 10.17487/RFC3849, July 2004,
              <https://www.rfc-editor.org/info/rfc3849>.

   [RFC5737]  Arkko, J., Cotton, M., and L. Vegoda, "IPv4 Address Blocks
              Reserved for Documentation", RFC 5737,
              DOI 10.17487/RFC5737, January 2010,
              <https://www.rfc-editor.org/info/rfc5737>.

   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, DOI 10.17487/RFC6761, February 2013,
              <https://www.rfc-editor.org/info/rfc6761>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/info/rfc6838>.

   [RFC6996]  Mitchell, J., "Autonomous System (AS) Reservation for
              Private Use", BCP 6, RFC 6996, DOI 10.17487/RFC6996, July
              2013, <https://www.rfc-editor.org/info/rfc6996>.

   [RFC7320]  Nottingham, M., "URI Design and Ownership", BCP 190,
              RFC 7320, DOI 10.17487/RFC7320, July 2014,
              <https://www.rfc-editor.org/info/rfc7320>.

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Appendix A.  JSend

   According to [JSend]:

      JSend is a specification that lays down some rules for how JSON
      responses from web servers should be formatted.  JSend focuses on
      application-level (as opposed to protocol- or transport-level)
      messaging which makes it ideal for use in REST-style applications
      and APIs.

   A basic JSend-compliant response must contain a "status" key and
   should contain "data", "message", and "code" keys dependent on the
   status value.  The following table lists the required and optional
   keys.

               +---------+-----------------+---------------+
               | Type    | Required keys   | Optional keys |
               +---------+-----------------+---------------+
               | success | status, data    |               |
               | fail    | status, data    |               |
               | error   | status, message | code, data    |
               +---------+-----------------+---------------+

                 Table 1: Type and Keys in JSend Response

Author's Address

   Markus Stubbig
   Independent
   Germany

   Email: stubbig.ietf@gmail.com

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