{% extends "global/layout.html" %}
{% block title %}I2NP Specification{% endblock %}
{% block lastupdated %}June 2013{% endblock %}
{% block accuratefor %}0.9.6{% endblock %}
{% block content %}
<h1>I2P Network Protocol (I2NP) Specification</h1>
<p>
The I2P Network Protocol (I2NP),
which is sandwiched between I2CP and the various I2P transport protocols, manages the
routing and mixing of messages between routers, as well as the selection of what
transports to use when communicating with a peer for which there are multiple
common transports supported.
</p>

<h2 id="structures">Common structures</h2>
The following structures are elements of multiple I2NP messages.
They are not complete messages.

<h3 id="struct_header">I2NP message header</h3>
<h4>Description</h4>
<p>
  Common header to all I2NP messages, which contains important information like a checksum, expiration date, etc.
</p>
<h4>Contents</h4>
<p>
  1 byte <a href="{{ site_url('docs/spec/common-structures') }}#type_Integer">Integer</a> specifying the type of this message,
 followed by a 4 byte <a href="{{ site_url('docs/spec/common-structures') }}#type_Integer">Integer</a> specifying the message-id.
 After that there is an expiration <a href="{{ site_url('docs/spec/common-structures') }}#type_Date">Date</a>,
 followed by a 2 byte <a href="{{ site_url('docs/spec/common-structures') }}#type_Integer">Integer</a> specifying
 the length of the message payload, followed by a <a href="{{ site_url('docs/spec/common-structures') }}#type_Hash">Hash</a>,
 which is truncated to the first byte. After that the actual message data follows.
</p>
{% highlight lang='dataspec' %}
Standard (16 bytes):

+----+----+----+----+----+----+----+----+
|type|      msg_id       |  expiration
+----+----+----+----+----+----+----+----+
                         |  size   |chks|
+----+----+----+----+----+----+----+----+

Short (SSU, 5 bytes):

+----+----+----+----+----+
|type| short_expiration  |
+----+----+----+----+----+

{% endhighlight %}

<h4>Definition</h4>
{% highlight lang='dataspec' %}
type :: Integer
        length -> 1 byte
        
        purpose -> identifies the message type (see table below)

msg_id :: Integer
          length -> 4 bytes

          purpose -> uniquely identifies this message (for some time at least)

expiration :: Date
           8 bytes
           date this message will expire

short_expiration :: Integer
           4 bytes
           date this message will expire (seconds since the epoch)

size :: Integer
        length -> 2 bytes
        
        purpose -> length of the payload

chks :: Integer
        length -> 1 byte
     
        purpose -> checksum of the payload
                   SHA256 hash truncated to the first byte

data :: Data
        length -> $size bytes
        
        purpose -> actual message contents
{% endhighlight %}
<h4>Notes</h4>
<ul><li>
When transmitted over <a href="{{ site_url('docs/transport/ssu') }}">SSU</a>,
the 16-byte standard header is not used.
Only a 1-byte type and a 4-byte expiration in seconds is included.
The message id and size are
incorporated into various parts of the SSU data packet format.
The checksum is not required since errors are caught in decryption.
</li><li>
The standard header is also required for I2NP messages contained in other messages and structures
(Data, TunnelData, TunnelGateway, and GarlicClove).
As of release 0.8.12, to reduce overhead, checksum verification is disabled at
some places in the protocol stack.
However, for compatibility with older versions, checksum generation is still required.
It is a topic for future research to determine points in the protocol stack
where the far-end router's version is known and checksum generation can be disabled.
</li></ul>


<h3 id="struct_BuildRequestRecord">BuildRequestRecord</h3>
<h4>Description</h4>
<p>
  One Record in a set of multiple records to request the creation of one hop in the tunnel. For more details see
  <a href="{{ site_url('docs/tunnels/implementation') }}">the tunnel overview</a> and
  <a href="{{ site_url('docs/spec/tunnel-creation') }}">the tunnel creation specification</a>.
</p>
<h4>Contents</h4>
<p>
  <a href="{{ site_url('docs/spec/common-structures') }}#type_TunnelId">TunnelId</a> to receive messages on, followed by the <a href="{{ site_url('docs/spec/common-structures') }}#type_Hash">Hash</a> of our <a href="{{ site_url('docs/spec/common-structures') }}#struct_RouterIdentity">RouterIdentity</a>. After that the <a href="{{ site_url('docs/spec/common-structures') }}#type_TunnelId">TunnelId</a> and the <a href="{{ site_url('docs/spec/common-structures') }}#type_Hash">Hash</a> of the next router's <a href="{{ site_url('docs/spec/common-structures') }}#struct_RouterIdentity">RouterIdentity</a> follow.
</p>
<h4>Definition</h4>
{% highlight lang='dataspec' %}
Cleartext:
+----+----+----+----+----+----+----+----+
| receive_tunnel    | our_ident         |
+----+----+----+----+                   +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+                   +----+----+----+----+
|                   | next_tunnel       |
+----+----+----+----+----+----+----+----+
| next_ident                            |
+                                       +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
| layer_key                             |
+                                       +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
| iv_key                                |
+                                       +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
| reply_key                             |
+                                       +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
| reply_iv                              |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
|flag| request_time      | send_msg_id
+----+----+----+----+----+----+----+----+
     |                                  |
+----+                                  +
|         29 bytes padding              |
+                                       +
|                                       |
+                             +----+----+
|                             |
+----+----+----+----+----+----+


ElGamal encrypted:
+----+----+----+----+----+----+----+----+
| toPeer                                |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
| encrypted data ...                    |
~                                       ~
|                                       |
+----+----+----+----+----+----+----+----+


ElGamal and AES encrypted:
+----+----+----+----+----+----+----+----+
| encrypted data ...                    |
~                                       ~
|                                       |
+----+----+----+----+----+----+----+----+
{% endhighlight %}

<h4>Definition</h4>
{% highlight lang='dataspec' %}
unencrypted:

receive_tunnel :: TunnelId
                  length -> 4 bytes
our_ident :: Hash
             length -> 32 bytes

next_tunnel :: TunnelId
               length -> 4 bytes

next_ident :: Hash
              length -> 32 bytes

layer_key :: SessionKey
             length -> 32 bytes

iv_key :: SessionKey
          length -> 32 bytes

reply_key :: SessionKey
             length -> 32 bytes

reply_iv :: data
            length -> 16 bytes

flag :: Integer
        length -> 1 byte

request_time :: Integer
                length -> 4 bytes
                Hours since the epoch, i.e. current time / 3600

send_message_id :: Integer
                   length -> 4 bytes

padding :: Data
           length -> 29 bytes
           source -> random

total length: 222


ElGamal encrypted:

toPeer :: First 16 bytes of the SHA-256 Hash of the peer's router identity
          length -> 16 bytes

encrypted_data :: ElGamal-2048 encrypted data (see notes)
                  length -> 512

total length: 528


ElGamal and AES encrypted:

encrypted_data :: ElGamal and AES encrypted data
                  length -> 528

total length: 528

{% endhighlight %}

<h4>Notes</h4>
<ul><li>
In the 512-byte encrypted record,
the ElGamal data contains bytes 1-256 and 258-513 of the
<a href="{{ site_url('docs/how/cryptography') }}#elgamal">514-byte ElGamal encrypted block</a>.
The two padding bytes from the block (the zero bytes at locations 0 and 257) are removed.
</li><li>
  See the <a href="{{ site_url('docs/spec/tunnel-creation') }}">tunnel creation specification</a> for details on field contents.
</li></ul>
</p>


<h3 id="struct_BuildResponseRecord">BuildResponseRecord</h3>
{% highlight lang='dataspec' %}
unencrypted:
+----+----+----+----+----+----+----+----+
|                                       |
+                                       +
|                                       |
+   SHA-256 Hash of following bytes     +
|                                       |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
| random data...                        |
~                                       ~
|                                       |
+                                  +----+
|                                  |ret |
+----+----+----+----+----+----+----+----+
{% endhighlight %}
<h4>Definition</h4>
{% highlight lang='dataspec' %}
unencrypted:
bytes 0-31   : SHA-256 Hash of bytes 32-527
bytes 32-526 : random data
byte  527    : reply

encrypted:
bytes 0-527: AES-encrypted record(note: same size as BuildRequestRecord)

total length: 528

{% endhighlight %}

<h4>Notes</h4>
<ul><li>
  The random data field could, in the future, be used to return congestion or peer connectivity information
  back to the requestor.
</li><li>
  See the <a href="{{ site_url('docs/spec/tunnel-creation') }}">tunnel creation specification</a> for details on the reply field.
</li></ul>


<h3 id="struct_GarlicClove">GarlicClove</h3>
{% highlight lang='dataspec' %}
unencrypted:
+----+----+----+----+----+----+----+----+
| Delivery Instructions                 |
~                                       ~
~                                       ~
|                                       |
+----+----+----+----+----+----+----+----+
| I2NP Message                          |
~                                       ~
~                                       ~
|                                       |
+----+----+----+----+----+----+----+----+
|    Clove ID       |     Expiration
+----+----+----+----+----+----+----+----+
                    | Certificate  |
+----+----+----+----+----+----+----+
{% endhighlight %}
<h4>Definition</h4>
<pre>
unencrypted:
Delivery Instructions :: <a href="{{ site_url('docs/spec/tunnel-message') }}#delivery">as defined here</a>
       Length varies but is typically 39, 43, or 47 bytes

I2NP Message :: Any I2NP Message

Clove ID :: 4 byte Integer

Expiration :: Date (8 bytes)

Certificate :: Always NULL in the current implementation (3 bytes total, all zeroes)

</pre>

<h4>Notes</h4>
<ul>
<li>
  Cloves are never fragmented.
  When used in a Garlic Clove, the first bit of the Delivery Instructions flag byte (the fragment bit) is redefined.
  If this bit is 0, the clove is not encrypted.
  If 1, the clove is encrypted, and a 32 byte Session Key immediately follows the flag byte.
  Clove encryption is not fully implemented.
<li>
  See also the <a href="{{ site_url('docs/how/garlic-routing') }}">garlic routing specification</a>.
<li>
  See also <a href="{{ site_url('docs/spec/tunnel-message') }}#delivery">Delivery Instructions definition</a>
<li>
  Maximum length is a function of the total length of all the cloves and the
  maximum length of the GarlicMessage.
<li>
  In the future, the certificate could possibly be used for a HashCash to "pay" for the routing.
<li>
  The message can be any I2NP message (including a GarlicMessage, although that is not used in practice).
  The messages used in practice are DataMessage, DeliveryStatusMessage, and DatabaseStoreMessage.
<li>
  The Clove ID is generally set to a random number on transmit and is checked for
  duplicates on receive (same message ID space as top-level Message IDs)
</ul>


<h3 id="struct_DeliveryInstructions">Delivery Instructions</h3>
Defined in the <a href="{{ site_url('docs/spec/tunnel-message') }}#delivery">Tunnel Message Specification</a>.


<h2 id="messages">Messages</h2>
<table border=1>
  <tr>
    <th>Message</th>
    <th>Type</th>
  </tr>
  <tr>
    <td><a href="#msg_DatabaseStore">DatabaseStore</a></td>
    <td align="right">1</td>
  </tr>
  <tr>
    <td><a href="#msg_DatabaseLookup">DatabaseLookup</a></td>
    <td align="right">2</td>
  </tr>
  <tr>
    <td><a href="#msg_DatabaseSearchReply">DatabaseSearchReply</a></td>
    <td align="right">3</td>
  </tr>
  <tr>
    <td><a href="#msg_DeliveryStatus">DeliveryStatus</a></td>
    <td align="right">10</td>
  </tr>
  <tr>
    <td><a href="#msg_Garlic">Garlic</a></td>
    <td align="right">11</td>
  </tr>
  <tr>
    <td><a href="#msg_TunnelData">TunnelData</a></td>
    <td align="right">18</td>
  </tr>
  <tr>
    <td><a href="#msg_TunnelGateway">TunnelGateway</a></td>
    <td align="right">19</td>
  </tr>
  <tr>
    <td><a href="#msg_Data">Data</a></td>
    <td align="right">20</td>
  </tr>
  <tr>
    <td><a href="#msg_TunnelBuild">TunnelBuild</a></td>
    <td align="right">21</td>
  </tr>
  <tr>
    <td><a href="#msg_TunnelBuildReply">TunnelBuildReply</a></td>
    <td align="right">22</td>
  </tr>
  <tr>
    <td><a href="#msg_VariableTunnelBuild">VariableTunnelBuild</a></td>
    <td align="right">23</td>
  </tr>
  <tr>
    <td><a href="#msg_VariableTunnelBuildReply">VariableTunnelBuildReply</a></td>
    <td align="right">24</td>
  </tr>
</table>

<h3 id="msg_DatabaseStore">DatabaseStore</h3>
<h4>Description</h4>
<p>
  An unsolicited database store, or the response to a successful Database Lookup Message
</p>
<h4>Contents</h4>
<p>
  An uncompressed LeaseSet or a compressed RouterInfo
</p>
{% highlight lang='dataspec' %}
with reply token:
+----+----+----+----+----+----+----+----+
| SHA256 Hash as key                    |
+                                       +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
|type| reply token       | reply tunnel-
+----+----+----+----+----+----+----+----+
 Id  | SHA256 of the gateway RouterInfo |
+----+                                  +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+    +----+----+----+----+----+----+----+
|    | data ...
+----+-//

with reply token == 0:
+----+----+----+----+----+----+----+----+
| SHA256 Hash as key                    |
+                                       +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
|type|         0         | data ...
+----+----+----+----+----+-//
{% endhighlight %}
<h4>Definition</h4>
<pre>
key:
    32 bytes
    SHA256 hash

type:
     1 byte
     type identifier
     mapping:
             0    RouterInfo
             1    LeaseSet

reply token:
            4 bytes
            If greater than zero, a <a href="#msg_DeliveryStatus">Delivery Status Message</a>
            is requested with the Message ID set to the value of the Reply Token.
            A floodfill router is also expected to flood the data to the closest floodfill peers
            if the token is greater than zero.

reply tunnelId:
               4 byte Tunnel ID
               only included if reply token &gt; 0
               This is the <a href="{{ site_url('docs/spec/common-structures') }}#type_TunnelID">tunnel ID</a> of the inbound gateway of the tunnel the response should be sent to

reply gateway:
              32 bytes
              Hash of the routerInfo entry to reach the gateway
              only included if reply token &gt; 0
              This is the router hash of the inbound gateway of the tunnel the response should be sent to

data:
     If type == 0, data is a 2-byte integer specifying the number of bytes that follow, followed by a gzip-compressed RouterInfo.
     If type == 1, data is an uncompressed LeaseSet.
</pre>

<h4>Notes</h4>
<ul><li>
For security, the reply fields are ignored if the message is received down a tunnel.
</li></ul>



<h3 id="msg_DatabaseLookup">DatabaseLookup</h3>
{% highlight lang='dataspec' %}
+----+----+----+----+----+----+----+----+
| SHA256 hash as the key to look up     |
+                                       +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
| SHA256 hash of the routerInfo         |
+ who is asking, or the gateway to      +
| send the reply to                     |
+                                       +
|                                       |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
|flag| reply_tunnelId    |size     |    |
+----+----+----+----+----+----+----+    +
| SHA256 of $key1 to exclude            |
+                                       +
|                                       |
+                                       +
|                                       |
+                                  +----+
|                                  |    |
+----+----+----+----+----+----+----+    +
| SHA256 of $key2 to exclude            |
+                                       +
~                                       ~
+                                  +----+
|                                  |    |
+----+----+----+----+----+----+----+    +
|                                       |
+                                       +
|   Session key if reply encryption     |
+   was requested                       +
|                                       |
+                                  +----+
|                                  |tags|
+----+----+----+----+----+----+----+----+
|                                       |
+                                       +
|   Session tags if reply encryption    |
+   was requested                       +
|                                       |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
{% endhighlight %}

<h4>Definition</h4>
{% highlight lang='dataspec' %}
key ::
    32 bytes
    SHA256 hash of the object to lookup

from ::
     32 bytes
     if deliveryFlag == 0, the SHA256 hash of the routerInfo entry this request came from (and to which the reply should be sent)
     if deliveryFlag == 1, the SHA256 hash of the reply tunnel gateway (to which the reply should be sent)

flags ::
     1 byte
     bit order: 76543210
     bit 0: deliveryFlag
             0  => send reply directly
             1  => send reply to some tunnel
     bit 1: encryptionFlag
             through release 0.9.5, must be set to 0
             as of release 0.9.6, ignored
             as of release 0.9.7:
             0  => send unencrypted reply
             1  => send AES encrypted reply using enclosed key and tag
     bits 7-2:
             through release 0.9.5, must be set to 0
             as of release 0.9.6, ignored, set to 0 for compatibility with future uses and with older routers

reply_tunnelId ::
               4 byte Tunnel ID
               only included if deliveryFlag == 1
               tunnelId of the tunnel to send the reply to

size ::
     2 byte Integer
     valid range: 0-512
     number of peers to exclude from the DatabaseSearchReply Message

excludedPeers ::
              $size SHA256 hashes of 32 bytes each (total $size*32 bytes)
              if the lookup fails, these peers are requested to be excluded from the list in
              the DatabaseSearchReply Message.
              if excludedPeers includes a hash of all zeroes, the request is exploratory, and
              the DatabaseSearchReply Message is requested to list non-floodfill routers only.

reply_key ::
     32 byte SessionKey
     only included if encryptionFlag == 1

tags ::
     1 byte Integer
     valid range: 1-32 (typically 1)
     the number of reply tags that follow
     only included if encryptionFlag == 1

reply_tags ::
     one or more 32 byte SessionTags (typically one)
     only included if encryptionFlag == 1

{% endhighlight %}

<h4>Notes</h4>
<ul><li>
Encryption flag, reply key, and reply tags are preliminary, not yet implemented.
</li><li>
Encrypted replies are only useful when the response is through a tunnel.
</li><li>
The number of included tags could be greater than one if alternative DHT lookup strategies
(for example, recursive lookups) are implemented.
</li></ul>


<h3 id="msg_DatabaseSearchReply">DatabaseSearchReply</h3>
<h4>Description</h4>
<p>
  The response to a failed Database Lookup Message
</p>
<h4>Contents</h4>
<p>
  A list of router hashes closest to the requested key
</p>
{% highlight lang='dataspec' %}
+----+----+----+----+----+----+----+----+
| SHA256 hash as query key              |
+                                       +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+----+----+----+----+----+----+----+----+
|num | peer_hash $1                     |
+----+                                  +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+    +----+----+----+----+----+----+----+
|    |                                  |
+----+ $num peer_hashes                 +

+    +----+----+----+----+----+----+----+
|    | from                             |
+----+                                  +
|                                       |
+                                       +
|                                       |
+                                       +
|                                       |
+    +----+----+----+----+----+----+----+
|    |
+----+


{% endhighlight %}

<h4>Definition</h4>
{% highlight lang='dataspec' %}
key ::
    32 bytes
    SHA256 of the object being searched

num ::
    1 byte Integer
    number of peer hashes that follow

peer_hash ::
          32 bytes
          SHA256 of the RouterInfo that the other router thinks are close to the key
          $num entries

from ::
     32 bytes
     SHA256 of the RouterInfo of the router this reply was sent from
{% endhighlight %}

<h4>Notes</h4>
<p>
  The 'from' hash is unauthenticated and cannot be trusted.
</p>

<h3 id="msg_DeliveryStatus">DeliveryStatus</h3>
<h4>Description</h4>
<p>
  A simple message acknowledgment. Generally created by the message originator, and wrapped
  in a Garlic Message with the message itself, to be returned by the destination.
</p>
<h4>Contents</h4>
<p>
  The ID of the delivered message, and the creation or arrival time.
</p>
{% highlight lang='dataspec' %}
+----+----+----+----+----+----+----+----+----+----+----+----+
|msg_id             |           time_stamp                  |
+----+----+----+----+----+----+----+----+----+----+----+----+
{% endhighlight %}

<h4>Definition</h4>
{% highlight lang='dataspec' %}
msg_id ::
       4 bytes
       unique ID of the message we deliver the DeliveryStatus for (see common I2NP header for details)

time_stamp :: Date
             8 bytes
             time the message was successfully created or delivered
{% endhighlight %}

<h4>Notes</h4>
<ul><li>
  It appears that the time stamp is always set by the creator to the current time.
  However there are several uses of this in the code, and more may be added in the future.
</li><li>
  This message is also used as a session established confirmation in <a href="{{ site_url('docs/transport/ssu') }}#establishDirect">SSU</a>.
  In this case, the message ID is set to a random number, and the
  "arrival time" is set to the current network-wide ID, which is 2
  (i.e. 0x0000000000000002).
</ul>

<h3 id="msg_Garlic">Garlic</h3>
<h4>Description</h4>
<p>
  Used to wrap multiple encrypted I2NP Messages
</p>
<h4>Contents</h4>
<p>
  When decrypted, a series of <a href="#struct_GarlicClove">Garlic Cloves</a>.
</p>
{% highlight lang='dataspec' %}
encrypted:
+----+----+----+----+----+----+----+----+
|      length       | data              |
+----+----+----+----+                   +
|                                       |
~                                       ~
~                                       ~
|                                       |
+----+----+----+----+----+----+----+----+


unencrypted data:
+----+----+----+----+----+----+----+----+
|num |  clove 1                         |
+----+                                  +
|                                       |
~                                       ~
~                                       ~
|                                       |
+----+----+----+----+----+----+----+----+
|         clove 2 ...                   |
~                                       ~
~                                       ~
|                                       |
+----+----+----+----+----+----+----+----+
| Certificate  |   Message_ID      |     
+----+----+----+----+----+----+----+----+
          Expiration               |
+----+----+----+----+----+----+----+
{% endhighlight %}

<h4>Definition</h4>
{% highlight lang='dataspec' %}
Encrypted:

length ::
       4 byte Integer
       number of bytes that follow 0 - 64 KB

data ::
     $length bytes
     ElGamal encrypted data


Unencrypted data:

num ::
     1 byte Integer number of GarlicCloves to follow

clove ::  a GarlicClove

Certificate :: always NULL in the current implementation (3 bytes total, all zeroes)

Message_ID :: 4 byte Integer

Expiration :: Date (8 bytes)

{% endhighlight %}

<h4>Notes</h4>
<ul>
<li>
  When unencrypted, data contains one or more <a href="#struct_GarlicClove">Garlic Cloves</a>.
<li>
  The AES encrypted block is padded to a minimum of 128 bytes; with the 32-byte Session Tag
  the minimum size of the encrypted message is 160 bytes; with the 4 length bytes
  the minimum size of the Garlic Message is 164 bytes.
<li>
  Actual max length is less than 64 KB; see the <a href="{{ site_url('docs/protocol/i2np') }}">I2NP Overview</a>.
<li>
  See also the <a href="{{ site_url('docs/how/elgamal-aes') }}">ElGamal/AES specification</a>.
<li>
  See also the <a href="{{ site_url('docs/how/garlic-routing') }}">garlic routing specification</a>.
<li>
  The 128 byte minimum size of the AES encrypted block is not currently configurable,
  however the minimum size of a DataMessage in a GarlicClove in a GarlicMessage, with
  overhead, is 128 bytes anyway. A configurable option to increase the minimum size
  may be added in the future.
<li>
  The message ID is generally set to a random number on transmit and
  appears to be ignored on receive.
<li>
  In the future, the certificate could possibly be used for a HashCash to "pay" for the routing.
</ul>


<h3 id="msg_TunnelData">TunnelData</h3>
{% highlight lang='dataspec' %}
+----+----+----+----+----+----+----+----+
|     tunnnelID     | data              |
+----+----+----+----+                   |
|                                       |
~                                       ~
~                                       ~
|                                       |
+                   +----+----+----+----+
|                   |
+----+----+----+----+
{% endhighlight %}

<h4>Definition</h4>
{% highlight lang='dataspec' %}
tunnelId ::
         4 byte Tunnel ID
         identifies the tunnel this message is directed at

data ::
     1024 bytes
     payload data.. fixed to 1024 bytes
{% endhighlight %}

<h4>Notes</h4>
<ul>
<li>
  See also the <a href="{{ site_url('docs/spec/tunnel-message') }}">Tunnel Message Specification</a>
</ul>


<h3 id="msg_TunnelGateway">TunnelGateway</h3>
{% highlight lang='dataspec' %}
+----+----+----+----+----+----+----+-//
| tunnelId          | length  | data...
+----+----+----+----+----+----+----+-//
{% endhighlight %}

<h4>Definition</h4>
{% highlight lang='dataspec' %}
tunnelId ::
         4 byte Tunnel ID
         identifies the tunnel this message is directed at

length ::
       2 byte Integer
       length of the payload

data ::
     $length bytes
     actual payload of this message
{% endhighlight %}

<h4>Notes</h4>
<ul>
<li>
  The payload is an I2NP message with a standard 16-byte header.
</ul>


<h3 id="msg_Data">Data</h3>
<h4>Description</h4>
<p>
  Used as a wrapper for encrypted Garlic Messages and Garlic Cloves.
  Also used previously for network load testing.
</p>
<h4>Contents</h4>
<p>
  A length Integer, followed by opaque data.
</p>
{% highlight lang='dataspec' %}
+----+----+----+----+----+-//
| length            | data...
+----+----+----+----+----+-//
{% endhighlight %}

<h4>Definition</h4>
{% highlight lang='dataspec' %}
length ::
       4 bytes
       length of the payload

data ::
     $length bytes
     actual payload of this message
{% endhighlight %}

<h3 id="msg_TunnelBuild">TunnelBuild</h3>
{% highlight lang='dataspec' %}
+----+----+----+----+----+----+----+----+
| Record 0 ...                          |

|                                       |
+----+----+----+----+----+----+----+----+
| Record 1 ...                          |

.....
+----+----+----+----+----+----+----+----+
| Record 7 ...                          |

|                                       |
+----+----+----+----+----+----+----+----+
{% endhighlight %}

<h4>Definition</h4>
{% highlight lang='dataspec' %}
Just 8 Build Request Records attached together
record size: 528 bytes
total size: 8*528 = 4224 bytes
{% endhighlight %}

<h4>Notes</h4>
<p>
  See also the <a href="{{ site_url('docs/spec/tunnel-creation') }}">tunnel creation specification</a>.
</p>


<h3 id="msg_TunnelBuildReply">TunnelBuildReply</h3>
{% highlight lang='dataspec' %}
same format as TunnelBuild message, with Build Response Records
{% endhighlight %}

<h4>Notes</h4>
<p>
  See also the <a href="{{ site_url('docs/spec/tunnel-creation') }}">tunnel creation specification</a>.
</p>

<h3 id="msg_VariableTunnelBuild">VariableTunnelBuild</h3>
{% highlight lang='dataspec' %}
+----+----+----+----+----+----+----+----+
|num | BuildRequestRecords...
+----+----+----+----+----+----+----+----+
{% endhighlight %}

<h4>Definition</h4>
{% highlight lang='dataspec' %}
Same format as TunnelBuildMessage, except for the addition of an "num" field in front and $num number of Build Request Records instead of 8

num ::
       1 byte Integer
       Valid values: 1-8

record size: 528 bytes
total size: 1 + $num*528
{% endhighlight %}

<h4>Notes</h4>
<ul>
<li>
  This message was introduced in router version 0.7.12, and may not be sent to tunnel participants earlier than that version.
<li>
  See also the <a href="{{ site_url('docs/spec/tunnel-creation') }}">tunnel creation specification</a>.
</ul>

<h3 id="msg_VariableTunnelBuildReply">VariableTunnelBuildReply</h3>
{% highlight lang='dataspec' %}
+----+----+----+----+----+----+----+----+
|num | BuildResponseRecords...
+----+----+----+----+----+----+----+----+
{% endhighlight %}

<h4>Definition</h4>
Same format as VariableTunnelBuild message, with Build Response Records.


<h4>Notes</h4>
<ul>
<li>
  This message was introduced in router version 0.7.12, and may not be sent to tunnel participants earlier than that version.
<li>
  See also the <a href="{{ site_url('docs/spec/tunnel-creation') }}">tunnel creation specification</a>.
</ul>



{% endblock %}