This document describes how nodes in a VPN find and connect to eachother and
maintain a stable network.
Copyright 2001 Guus Sliepen
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$Id: CONNECTIVITY,v 1.1.2.1 2001/07/22 14:04:38 guus Exp $
1. Problem
==========
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
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.