This document describes how nodes in a VPN find and connect to eachother and
maintain a stable network.
- Copyright 2001 Guus Sliepen <guus@sliepen.warande.net>
+ Copyright 2001-2006 Guus Sliepen <guus@tinc-vpn.org>
Permission is granted to make and distribute verbatim copies of
this documentation provided the copyright notice and this
provided that the entire resulting derived work is distributed
under the terms of a permission notice identical to this one.
- $Id: CONNECTIVITY,v 1.1.2.1 2001/07/22 14:04:38 guus Exp $
-
-1. Problem
+1. Synchronisation
+==================
+
+Each tinc daemon has zero or more connections to other tinc daemons. It will
+try to keep its own information synchronised with the other tinc daemons. If
+one of its peers sends information, the tinc daemon will check if it is new
+information. If so, it will update its own information and forward the new
+information to all the other peers.
+
+This scheme will make sure that after a short amount of time all tinc daemons
+share the same information. It will also almost completely prevent information
+from looping, because "new" information that is already known is ignored and
+not forwarded any further. However, since information can also be deleted
+there's the possibility of a looping sequence of add/delete messages. This is
+resolved by additionaly adding a unique identifier to each broadcasted message.
+Messages are dropped if the same message with that identifier has already been
+seen.
+
+2. Routing
==========
-We have a set of nodes (A, B, C, ...) that are part of the same VPN. They need
-to connect to eachother and form a single graph that satisfies the tree
-property.
-
-There is the possibility that loops are formed, the offending connections must
-be eliminated.
-
-Suppose we start with two smaller graphs that want to form a single larger
-graph. Both graphs consist of three nodes:
-
- A-----B-----C
-
-
-
- D-----E-----F
-
-It is very well possible that A wants to connect to D, and F wants to connect
-to C, both at the same time. The following loop will occur:
-
- A-----B-----C
- | ^
- | |
- v |
- D-----E-----F
+Every node tells its peers to which other peers it is connected. This way
+every node will eventually know every connection every node has on the VPN.
+Each node will use graph algorithms to determine if other nodes are reachable or not and
+what the best route is to other nodes.
-The situation described here is totally symmetric, there is no preference to
-one connection over the other. The problem of resolving the loop, maintaining
-consistency and stability is therefore not a trivial one.
+Because all nodes share the same information, using a deterministic algorithm
+each node will calculate the same minimum spanning tree for the entire VPN.
+The MST will be used to send broadcast VPN packets.
projects / tinc / blobdiff