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| </head> |
| <body class="article"> |
| <div id="header"> |
| <h1>ZeroTier Mapping for Scalability Protocols</h1> |
| <div class="details"> |
| <span id="author" class="author">Garrett D'Amore</span><br> |
| <span id="email" class="email"><a href="mailto:garrett@damore.org">garrett@damore.org</a></span><br> |
| <span id="revnumber">version 0.10,</span> |
| <span id="revdate">2018-03-05</span> |
| </div> |
| </div> |
| <div id="content"> |
| <div id="preamble"> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p><span class="image"><img src="https://img.shields.io/badge/status-draft-yellow.svg?style=for-the-badge" alt="draft"></span></p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_zerotier_mapping_for_scalability_protocols">ZeroTier Mapping for Scalability Protocols</h2> |
| <div class="sectionbody"> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>Status: draft</p> |
| </li> |
| <li> |
| <p>Authors: <a href="mailto:garrett@damore.org">Garrett D’Amore</a></p> |
| </li> |
| <li> |
| <p>Version 0.10</p> |
| </li> |
| </ul> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_abstract">Abstract</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>This document defines the |
| <a href="http://www.zerotier.com">ZeroTier</a> mapping for scalability protocols. |
| This enables SP protocols to run over a ZeroTier network. The transport |
| defined here sits on top of an unreliable virtual Layer 2 transport, |
| and does not require a TCP/IP stack.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_license">License</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Copyright 2018 <a href="mailto:info@staysail.tech">Staysail Systems, Inc.</a><br> |
| Copyright 2018 <a href="mailto:info@capitar.com">Capitar IT Group BV</a></p> |
| </div> |
| <div class="paragraph"> |
| <p>This specification is licensed under the Apache License, Version 2.0 |
| (the "License"); you may not use this file except in compliance with the |
| License. |
| You may obtain a copy of the license |
| <a href="http://www.apache.org/licenses/LICENSE-2.0">online</a>.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_language">Language</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", |
| "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be |
| interpreted as described in <a href="https://tools.ietf.org/html/rfc2119">RFC 2119</a>.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_underlying_protocol">Underlying protocol</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>ZeroTier expresses an 802.3 style layer 2, where frames maybe exchanged as if |
| they were Ethernet frames. Virtual broadcast domains are created within a |
| numbered "network", and frames may then be exchanged with any peers on that |
| network.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Frames may arrive in any order, or be lost, just a with Ethernet |
| (best effort delivery), but they are strongly protected by a |
| cryptographic checksum, so frames that do arrive will be uncorrupted. |
| Furthermore, ZeroTier guarantees that a given frame will be received |
| at most once.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Each application on a ZeroTier network has its own address<sup class="footnote">[<a id="_footnoteref_1" class="footnote" href="#_footnote_1" title="View footnote.">1</a>]</sup>, |
| called a |
| ZeroTier ID (<em>ZTID</em>), which is globally unique — this is generated |
| from a hash of the public key associated with the application.</p> |
| </div> |
| <div class="paragraph"> |
| <p>A given application may participate in multiple ZeroTier networks.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Sharing of ZeroTier IDs between applications, as well as use of multiple |
| <em>ZTID</em> values within a single application, as well as management of the |
| associated ZeroTier-specific state is out of scope for this document.</p> |
| </div> |
| <div class="paragraph"> |
| <p>ZeroTier networks have a standard MTU of 2800 bytes, but over typical |
| public networks an "optimum" MTU of 1400 bytes is used. |
| ZeroTier may be configured to have larger MTUs, but typically this involves |
| extensive reassembly at underlying layers, and implementations <strong>SHOULD</strong> |
| use the optimum MTU advertised by the ZeroTier implementation.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Note that at this time, broadcast and multicast is not supported by |
| this mapping. (A future update may resolve this.)</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_packet_layout">Packet layout</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Each SP message sent over ZeroTier is comprised of one or |
| more fragments, where each fragment is mapped to a single underlying |
| ZeroTier L2 frame. We use the EtherType field of 0x0901 to indicate |
| SP over ZeroTier protocol (number to be registered with IEEE).</p> |
| </div> |
| <div class="paragraph"> |
| <p>The ZeroTier L2 payload shall be encoded with a header as follows:</p> |
| </div> |
| <div class="imageblock"> |
| <div class="content"> |
| <img src="zerotier0-header.png" alt="zerotier0 header" width="896" height="360"> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>All numeric fields are in big-endian byte order. Note that ZeroTier |
| APIs present this as the L2 payload, but ZeroTier itself may prepend |
| additional data such as the Ethernet type, and source and destination |
| MAC addresses, as well as ZeroTier specific headers. The details of |
| such headers are out of scope for this document.</p> |
| </div> |
| <div class="paragraph"> |
| <p>As above, the start of each frame is just as a normal Ethernet payload. |
| The Ethernet type (ethertype) we use for these frames is 0x901, with |
| a VLAN ID of 0.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The <code>op</code> is a field that indicates the type of message being sent. The |
| following values are defined:</p> |
| </div> |
| <table class="tableblock frame-all grid-all spread"> |
| <colgroup> |
| <col style="width: 20%;"> |
| <col style="width: 80%;"> |
| </colgroup> |
| <tbody> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x00</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a href="#_data_messages"><code>DATA</code></a></p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x10</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a href="#_conn_req_and_conn_ack_messages"><code>CONN-REQ</code></a></p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x12</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a href="#_conn_req_and_conn_ack_messages"><code>CONN-ACK</code></a></p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x20</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a href="#_disc_messages"><code>DISC</code></a></p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x30</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a href="#_ping_and_pong_messages"><code>PING</code></a></p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x32</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a href="#_ping_and_pong_messages"><code>PONG</code></a></p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x40</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock"><a href="#_err_messages"><code>ERR</code></a></p></td> |
| </tr> |
| </tbody> |
| </table> |
| <div class="paragraph"> |
| <p>These are discussed further below. Implementations |
| <strong>MUST</strong> discard messages where the <code>op</code> is not one of these.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The <code>flags</code> field is reserved for future use, and <strong>MUST</strong> be zero. |
| Implementations <strong>MUST</strong> discard frames for which this is not true.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The <code>version</code> byte <strong>MUST</strong> be set to <code>0x1</code>. Implementations <strong>MUST</strong> discard |
| any messages received for any other version.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The <code>source port</code> and <code>destination port</code> are used to construct a logical |
| conversation. These are 24-bits wide, and are discussed further below. |
| The <code>reserved</code> fields must be set to zero.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The remainder of frame varies depending on the <code>op</code> used.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Note that it is not by accident that the payload is 32-bit aligned in |
| this message format. The payload is actually 64-bit aligned.</p> |
| </div> |
| <div class="sect2"> |
| <h3 id="_port_fields">Port Fields</h3> |
| <div class="paragraph"> |
| <p>The port fields are used to discriminate different uses, allowing one |
| application to have multiple connections or sockets open. The |
| purpose is analogous to TCP port numbers, except that instead of the |
| operating system performing the discrimination the application or |
| library code must do so. Note that port numbers are 24-bits. This |
| was chosen to allow a peer to allocate a unique port number for each |
| local conversation, allowing up to 16 million concurrent conversations. |
| This also allows a 40-bit node number to be combined with the 24-bit |
| port number to create a 64-bit unique address.</p> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_data_messages">DATA messages</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p><code>DATA</code> messages carry SP protocol payload data. They can only be sent |
| on an established session (see <code>CONN</code> messages below), and are never |
| acknowledged (in this version). The op-specific payload they carry |
| is formed like this:</p> |
| </div> |
| <div class="imageblock"> |
| <div class="content"> |
| <img src="zerotier0-data.png" alt="zerotier0 data" width="896" height="240"> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>All fragments, except for the last, <strong>MUST</strong> be the same size. The fragment |
| size field carries the size of every fragment, except that the last |
| fragment may be shorter; however even for the last fragment, the fragment |
| size <strong>MUST</strong> be the size of the rest of the fragments. This is necessary |
| to allow a receiver to know the fragment size of the other fragments even |
| if the final fragment is received before any others. (Typically this may |
| occur if a message consisting of two fragments arrives with fragments |
| out of order.)</p> |
| </div> |
| <div class="paragraph"> |
| <p>The last fragment shall have the fragment number equal to |
| the total fragments minus one, and the first fragment shall have fragment |
| number 0. Under typical optimal conditions, with an optimal MTU of 1400 |
| bytes, the largest message that can be transmitted is approximately 86 MB. |
| Specifically the limit is (65534 * (1400 - 20)) = 90,436,920 bytes. |
| (Larger MTUs may be used, if the implementation determines that it is |
| advantageous to do so. Doing so would necessarily give a larger maximum |
| message size.)</p> |
| </div> |
| <div class="paragraph"> |
| <p>However, transmitting such a large message would require sending over |
| 65 thousand fragments, and given the likelihood of fragment loss, and |
| the lack of acknowledgment, it is likely that the entire message would |
| be lost. As a result, implementations are encouraged to limit the |
| amount of data that they send to at most a few megabytes. Implementations |
| receiving the first fragment can easily calculate the worst case for |
| the message size (the size of the user payload multiplied by the total |
| number of fragments), and <strong>MAY</strong> reply to the sender with an <code>ERR</code> message |
| using the code 0x05, indicating that the message is larger than the |
| receiver is willing to accept.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Each fragment for a given message must carry the same <code>message ID</code>. |
| Implementations <strong>MUST</strong> initialize this to a random value when starting |
| a conversation, and <strong>MUST</strong> increment this each time a new message is sent. |
| Message IDs of zero are not permitted; implementations <strong>MUST</strong> skip past zero |
| when incrementing message IDs.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Implementations may detect the loss of a message by noticing skips in the |
| message IDs that are received, accounting for the expected skip past zero.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Note that no field conveys the length of the fragment itself, as |
| this can be determined from the L2 length — the user data within |
| the fragment extends to the end of the L2 payload supplied by ZeroTier. |
| (And, all fragments other than the final fragment for a message must |
| therefore have the same length.)</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_conn_req_and_conn_ack_messages">CONN-REQ and CONN-ACK messages</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p><code>CONN-REQ</code> frames represent a request from an initiator to establish a |
| session, i.e. a new conversation or connection, and <code>CONN-ACK</code> |
| messages are the normal successful reply from the responder. They both |
| take the same form, which consists of the usual headers along with the |
| senders 16-bit (big-endian) SP protocol ID appended:</p> |
| </div> |
| <div class="imageblock"> |
| <div class="content"> |
| <img src="zerotier0-conn.png" alt="zerotier0 conn" width="536" height="160"> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>The connection is initiated by the initiator sending this message, |
| with its own SP protocol ID, with the <code>op</code> set to <code>CONN-REQ</code>. |
| The initiator must choose a <code>source port</code> number that is not currently |
| being used with the remote peer. (Most implementations will choose a |
| a source port that is not used at all. Source port numbers <strong>SHOULD</strong> |
| be chosen randomly.)</p> |
| </div> |
| <div class="paragraph"> |
| <p>The responder will acknowledge this by replying with its SP protocol |
| ID in the 4-byte payload, using the <code>CONN-ACK</code> op. Additionally, |
| the source port number that the responder replies with <strong>MUST</strong> be the |
| one the intiator requested.</p> |
| </div> |
| <div class="paragraph"> |
| <p>(Responders will identify the session using the initiators chosen |
| <code>source port</code>, which the initiator <strong>MUST NOT</strong> concurrently use for any |
| other sessions.)</p> |
| </div> |
| <div class="paragraph"> |
| <p>Alternatively, a responder <strong>MAY</strong> reject the connection attempt by |
| sending a suitably formed ERR message (see below).</p> |
| </div> |
| <div class="paragraph"> |
| <p>If a sender does not receive a reply, it <strong>SHOULD</strong> retry this message |
| before giving up and reporting an error to the user. It is recommended |
| that a configurable number of retries and time interval be used.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Given modern Internet latencies of generally less than 500 ms, resending |
| up to 12 <code>CONN-REQ</code> requests, once every 5 seconds, before giving up seems |
| reasonable. (These times are somewhat larger to allow for ZeroTier |
| path discovery to take place; this results in a timeout of approximately |
| a minute.)</p> |
| </div> |
| <div class="paragraph"> |
| <p>The initiator <strong>MUST NOT</strong> send any <code>DATA</code> messages for a conversation until |
| it has received an ACK from the other party, and it <strong>MUST</strong> send all further |
| messages for the conversation to the port number supplied by the responder.</p> |
| </div> |
| <div class="paragraph"> |
| <p>If a <code>CONN-REQ</code> frame is received by a responder for a conversation that already |
| exists, the responder <strong>MUST</strong> reply. Further, the source port it replies with, |
| and the SP protocol IDs <strong>MUST</strong> be identical to what it first sent. This |
| ensures that the <code>CONN-REQ</code> request is idempotent.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_disc_messages">DISC messages</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>DISC messages are used to request a session be terminated. This |
| notifies the remote sender that no more data will be sent or |
| accepted, and the session resources may be released. There is no |
| payload. There is no acknowledgment.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_ping_and_pong_messages">PING and PONG messages</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>In order to keep session state, implementations will generally store |
| data for each session. In order to prevent a stale session from |
| consuming these resources forever, and in order to keep underlying |
| ZeroTier sessions alive, a <code>PING</code> message <strong>MAY</strong> be sent to a peer |
| with whom a session has been established. This message has no payload.</p> |
| </div> |
| <div class="paragraph"> |
| <p>If the <code>PING</code> is is successful, then the responder <strong>MUST</strong> reply with a <code>PONG</code> |
| message. As with <code>PING</code>, the <code>PONG</code> message carries no payload.</p> |
| </div> |
| <div class="paragraph"> |
| <p>There is no response to a <code>PONG</code> message.</p> |
| </div> |
| <div class="paragraph"> |
| <p>In the event of an error, an implementation <strong>MAY</strong> reply with an <code>ERR</code> |
| message.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Implementations <strong>SHOULD NOT</strong> initiate <code>PING</code> messages if they have either |
| received other session messages recently.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Implementations <strong>SHOULD</strong> use a timeout <em>T1</em> seconds of be used before |
| initiating a message the first time, and that in the absence of a |
| reply, up to <em>N</em> further attempts be made, separated by <em>T2</em> seconds. If |
| no reply to the <em>N_th attempt is received after _T2</em> seconds have passed, |
| then the remote peer should be assumed offline or dead, and the |
| session closed.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The values for <em>T1</em>, <em>T2</em>, and <em>N</em> <strong>SHOULD</strong> be configurable, with |
| recommended default values of 60, 10, and 5. With these values, |
| sessions that appear dead after 2 minutes will be closed, and their |
| resources reclaimed.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_err_messages">ERR messages</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p><code>ERR</code> messages indicate a failure in the session, and abruptly |
| terminate the session. The payload for these messages consists of a |
| single byte error code, followed by an ASCII message describing the |
| error (not terminated by zero). This message <strong>MUST NOT</strong> be more than |
| 128 bytes in length.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The following error codes are defined:</p> |
| </div> |
| <table class="tableblock frame-all grid-all spread"> |
| <colgroup> |
| <col style="width: 20%;"> |
| <col style="width: 80%;"> |
| </colgroup> |
| <tbody> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x01</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">No party listening at that address or port.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x02</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">No such session found.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x03</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">SP protocol ID invalid.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x04</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">Generic protocol error.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0x05</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">Message size too big.</p></td> |
| </tr> |
| <tr> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">0xff</p></td> |
| <td class="tableblock halign-left valign-top"><p class="tableblock">Other uncategorized error.</p></td> |
| </tr> |
| </tbody> |
| </table> |
| <div class="paragraph"> |
| <p>Implementations <strong>MUST</strong> discard any session state upon receiving an <code>ERR</code> |
| message. These messages are not acknowledged.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_message_reassembly">Message Reassembly</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Implementations <strong>MUST</strong> accept and reassemble fragmented <code>DATA</code> messages. |
| Implementations <strong>MUST</strong> discard fragmented messages of other types.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Messages larger than the ZeroTier MTU <strong>MUST</strong> be fragmented.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Implementations SHOULD limit the number of unassembled messages |
| retained for reassembly, to minimize the likelihood of intentional |
| abuse. It is suggested that at most 2 unassembled messages be |
| retained. It is further suggested that if 2 or more unfragmented |
| messages arrive before a message is reassembled, or more than 5 |
| seconds pass before the reassembly is complete, that the unassembled |
| fragments be discarded.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_ports">Ports</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>The port numbers are 24-bit fields, allowing a single <em>ZTID</em> to |
| service multiple application layer protocols, which could be treated |
| as separate end points, or as separate sockets in the application. |
| The implementation is responsible for discriminating on these and |
| delivering to the appropriate consumer.</p> |
| </div> |
| <div class="paragraph"> |
| <p>As with UDP or TCP, it is intended that each party have its own port |
| number, and that a pair of ports (combined with ZeroTier IDs) be used |
| to identify a single conversation.</p> |
| </div> |
| <div class="paragraph"> |
| <p>An SP server <strong>SHOULD</strong> allocate a port for number advertisement. It is |
| expected clients will generate ephemeral port numbers.</p> |
| </div> |
| <div class="paragraph"> |
| <p>Implementations are free to choose how to allocate port numbers, but |
| it is <strong>RECOMMENDED</strong> that administratively configured port numbers are small, |
| with the high order bit clear, and that numbers larger than 2<sup>23</sup> (high order |
| bit set) be used for ephemeral allocations.</p> |
| </div> |
| <div class="paragraph"> |
| <p>It is <strong>RECOMMENDED</strong> that separate short queues (perhaps just one or two |
| messages long) be kept per local port in implementations, to prevent |
| head-of-line blocking issues where backpressure on one consumer |
| (perhaps just a single thread or socket) blocks others.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_uri_format">URI Format</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>The URI scheme used to represent ZeroTier addresses makes use of |
| ZeroTier IDs, ZeroTier network IDs, and our own 24-bit ports.</p> |
| </div> |
| <div class="paragraph"> |
| <p>The format <strong>SHALL</strong> be <code>zt://<em>ztid</em>.<em>nwid</em>:<em>port</em></code>, where the <code><em>nwid</em></code> |
| component represents the 64-bit hexadecimal ZeroTier network ID, |
| the <code><em>ztid</em></code> represents the 40-bit hexadecimal ZeroTier Device ID, |
| and the <code><em>port</em></code> is the 24-bit port number (decimal) previously described.</p> |
| </div> |
| <div class="paragraph"> |
| <p>An implementation <strong>MAY</strong> allow the <code><em>ztid</em></code> 0 be replaced with <code>*</code> to |
| indicate that the node’s local <em>ZTID</em> be used.</p> |
| </div> |
| <div class="paragraph"> |
| <p>An implementation <strong>MAY</strong> permit the use of port number of 0 when listening, |
| to indicate that a random ephemeral port should be chosen.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_security_considerations">Security Considerations</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>The mapping isn’t intended to provide any additional security beyond that |
| provided by ZeroTier itself. Managing the key materials used by ZeroTier |
| is implementation-specific, and they must take the appropriate care when |
| dealing with them.</p> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div id="footnotes"> |
| <hr> |
| <div class="footnote" id="_footnote_1"> |
| <a href="#_footnoteref_1">1</a>. Technically an application may have more than one ZeroTier address, but such uses are unusual. |
| </div> |
| </div> |
| <div id="footer"> |
| <div id="footer-text"> |
| Version 0.10<br> |
| Last updated 2018-03-05 22:59:54 UTC |
| </div> |
| </div> |
| </body> |
| </html> |