n2n_v2

Section: Background (7)
Updated: Sep 21, 2009
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NAME

N2n Version 2 - version 2 of the n2n decentralised peer-to-peer network overlay VPN.

DESCRIPTION

N2n is a peer-to-peer network overlay or VPN system that provides layer 2 over layer 3 encapsulation with data transform capabilities such as encryption and compression. This guide discusses the differences of version 2 or n2n from version 1.

PROTOCOLS

N2n-2 uses a different set of messages to communicate with edges and supernodes. The n2n-2 messages are not compatible with n2n-1. There is no backward compatibility for n2n-1.

ENCRYPTION

N2n-2 offers a new way of handling encryption compared to n2n-1. N2n-1 provided facility for a single community password with no expiration. In n2n-2 this method is preserved but a new mechanism has been added using a key schedule file.

Key Schedule: A key schedule file lists a number of keys with the period for which each is valid along with the encryption type identifier and the actual key value. This allows the user to define up to 32 keys in advance with a pre-set time at which they keys will change. The key schedule file can be reloaded while the edge is running to allow new keys to be loaded and unused keys expunged.
Timing Requirements When a key rolls over to the next in the schedule, the new: key is used for all transmitted packets; however any packets received using an older key can still be decoded as the keys from the key schedule are still known. As a result edges do not need to have accurate time synchronisation. The accuracy of required synchronisation depends to a large degree on the key schedule. Rapid key roll-overs requires more accurate time synchronisation.

N2n-2 provides the following encryption ciphers; more can be added as required:

(1) NULL: Data is encapsulated unchanged. Useful for testing and high-performance, low sensitivity applications.
(2) TF: Twofish AES candidate.

The following additional ciphers are specified but not yet implemented:

(3) AES-CBC: AES in CBC mode with 256-bit key.
(4) LZO: LZO compression of data (no encryption).
(5) TF-LZO: TF cipher with LZO compression of data prior to encryption.
(6) AES-CBC-LZO: AES-CBC ciper with LZO compression of data prior to encryption.

EXTENSIBILITY

N2n-2 decouples the data transform system from the core of the edge operation. This allows for easier addition of new data transform operations. N2n-2 reserves 64 standard transform identifiers (such as TwoFish encryption) but allocates transform identifiers 64 - 65536 for user-defined transforms. This allows anyone to add to n2n new private transforms without breaking compatibility with the standard offering.

MULTIPLE SUPERNODES

N2n-2 introduces the capability of multiple supernodes to be used by an edge. N2n-2 offers supernode in several flavours:

Stand-alone supernode

This is the same concept as from n2n-1. Supernode is a small efficient C program which operates in isolation.

Federated supernodes

This is a cluster of supernodes which share information. Edges registered to any of the cooperating supernodes can relay packets through the supernode federation and switch supernodes if required. Supernodes can send PACKET or REGISTER messages to other supernodes to try and find the destination edge.

The n2n-2 edge implementation allows multiple supernodes to be specified on the command line. Edges monitor the current supernode for responses to REGISTER_SUPER messages. If 3 responses are missed then the edge starts looking for a new supernode. It cycles through the list of supernodes specified until it finds a working one.

EFFICIENCY

The n2n-2 message formats have been made more efficient. The amount of data overhead has been reduced by ensuring the messages contain only the data fields required. Some optional fields do not consume data if they are not present.

DAEMON OPERATION

The supernode and edge use daemon mode of operation by default. This sense is inverted from n2n-1 where they ran in the foreground by default. They can be made to run in the foreground so tools such a DJB's daemontools can work with them. See the -f option

MANAGEMENT CONSOLE

Edge and supernode in n2n-2 provide a UDP-based management console. Both listen on the localhost address 127.0.0.1. Commands can be sent to the programs by sending to the UDP socket. Responses are returned to the socket from which commands were issued. This only works from the computer on which the programs are running. Statistics can be retrieved and commands issued. The netcat utility is all that is required; but more sophisticated tools could be built on the interface.

SUPERNODE AUTHENTICATION

(To be implemented) Space has been reserved in the supernode registration messages for an authentication mechanism.

MESSAGE SUMMARY

The following message types work within n2n-2.

REGISTER_SUPER: Sent from an edge to its local supernode to register its MAC with the community.
REGISTER_SUPER_ACK: Sent from a supernode to an edge to confirm registration. This also carries the definition of the edge socket as seen at the supernode so NAT can be detected and described.
REGISTER_SUPER_NAK: Supernode refusing to register an edge.
PACKET: Encapsulated ethernet packets sent between edges. Supernodes forward or broadcast these and edges send them direct in peer-to-peer mode.
REGISTER: A peer-to-peer mode registration request from one edge to another. Supernodes forward these to facilitate NAT crossing introductions.
REGISTER_ACK: Complete peer-to-peer mode setup between two edges. These messages need to travel direct between edges.
FEDERATION: Federated supernodes exchanging community information.

OTHER DIFFERENCES

HTTP Tunneling: This experimental feature (-t option in n2n_v1) of n2n_v1 has been removed entirely from n2n_v2.

AUTHORS

Richard Andrews andrews (at) ntop.org - main author of n2n-2
Luca Deri: deri (at) ntop.org - code inherited from n2n-1

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