This document describes how nodes in a VPN find and connect to eachother and maintain a stable network. Copyright 2001 Guus Sliepen Permission is granted to make and distribute verbatim copies of this documentation provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this documentation under the conditions for verbatim copying, 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 ========== 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.