A última atualização desta página foi em June 2013 e é própria para a versão de servidor 0.9.6.

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.

I2NP Definition

I2NP (I2P Network Protocol) messages can be used for one-hop, router-to-router, point-to-point messages. By encrypting and wrapping messages in other messages, they can be sent in a secure way through multiple hops to the ultimate destination. Priority is only used locally at the origin, i.e. when queuing for outbound delivery.

The priorities listed below may not be current and are subject to change. See the OutNetMessage Javadocs for the current priority settings. Priority queueing implementation may vary.

Message Format

Unique ID4
Payload Length2
Payload0 - 61.2KB

While the maximum payload size is nominally 64KB, the size is further constrained by the method of fragmenting I2NP messages into multiple 1KB tunnel messages as described on the tunnel implementation page. The maximum number of fragments is 64, and the message may not be perfectly aligned, So the message must nominally fit in 63 fragments.

The maximum size of an initial fragment is 956 bytes (assuming TUNNEL delivery mode); the maximum size of a follow-on fragment is 996 bytes. Therefore the maximum size is approximately 956 + (62 * 996) = 62708 bytes, or 61.2 KB.

In addition, the transports may have additional restrictions. NTCP currently limits to 16KB - 6 = 16378 bytes but this will be increased in a future release. The SSU limit is approximately 32 KB.

Note that these are not the limits for datagrams that the client sees, as the router may bundle a reply leaseset and/or session tags together with the client message in a garlic message. The leaseset and tags together may add about 5.5KB. Therefore the current datagram limit is about 10KB. This limit will be increased in a future release.

Message Types

Higher-numbered priority is higher priority. The majority of traffic is TunnelDataMessages (priority 400), so anything above 400 is essentially high priority, and anything below is low priority. Note also that many of the messages are generally routed through exploratory tunnels, not client tunnels, and therefore may not be in the same queue unless the first hops happen to be on the same peer.

Also, not all message types are sent unencrypted. For example, when testing a tunnel, the router wraps a DeliveryStatusMessage, which is wrapped in a GarlicMessage, which is wrapped in a DataMessage.

Message Type Payload Length Priority Comments
DatabaseLookupMessage 2   500 May vary
DatabaseSearchReplyMessage 3 Typ. 161 300 Size is 65 + 32*(number of hashes) where typically, the hashes for three floodfill routers are returned.
DatabaseStoreMessage 1 Varies 460 Priority may vary. Size is 898 bytes for a typical 2-lease leaseSet. RouterInfo structures are compressed, and size varies; however there is a continuing effort to reduce the amount of data published in a RouterInfo as we approach release 1.0.
DataMessage 20 4 - 62080 425 Priority may vary on a per-destination basis
DeliveryStatusMessage 10 12   Used for message replies, and for testing tunnels - generally wrapped in a GarlicMessage
GarlicMessage 11     Generally wrapped in a DataMessage - but when unwrapped, given a priority of 100 by the forwarding router
TunnelBuildMessage 21 4224 500
TunnelBuildReplyMessage 22 4224 300
TunnelDataMessage 18 1028 400 The most common message. Priority for tunnel participants, outbound endpoints, and inbound gateways was reduced to 200 as of release Outbound gateway messages (i.e. those originated locally) remains at 400.
TunnelGatewayMessage 19   300/400
VariableTunnelBuildMessage 23 1057 - 4225 500 Shorter TunnelBuildMessage as of 0.7.12
VariableTunnelBuildReplyMessage 24 1057 - 4225 300 Shorter TunnelBuildReplyMessage as of 0.7.12
Others listed in 2003 Spec 0,4-9,12     Obsolete, Unused

Full Protocol Specification

On the I2NP Specification page. See also the Common Data Structure Specification page.

Future Work

It isn't clear whether the current priority scheme is generally effective, and whether the priorities for various messages should be adjusted further. This is a topic for further research, analysis and testing.