The domains in a tree share a namespace. The trees that are joined together at the top level of the forest do not share the same namespace. The trees with a forest share the following characteristics:

• configuration data
  all domains in the forest know the domain topology which is replicated immediately to all domains when a new domain joins the forest. The data includes connection objects, sites, ip subnets, site links, bridges
  the schema defines the legal object classes and attributes
• global catalog

will use this tip as an index for forest as I add links and info