Creation of Trusts:-
Trusts are created in 2 ways:

Explicitly (Manually)
Implicitly (Automatically)

Transitivity of Trusts:-

Transitive
Non Transitive

1. Transitive Trust:-

Domain A trusts Domain B,
Domain B trusts Domain C,
Then, Domain C trusts Domain A

2. Non – Transitive Trust:-Domain A trusts Domain B

Domain B trusts Domain C
There is no trust relationship between Domain A and Domain C

Direction of Trust:-

One Way
Two Way

1. One Way:-

This is a single trust relationship where only Domain A trusts Domain B
One way relationship may be either Transitive or Non Transitive depending on the type of trust that is created.

2. Two Way:-

In this method the trust is in both ways. Domain A trusts Domain B and Domain B trusts Domain A (vice versa)
The authentication request passes in both ways.

Forms of Trust:-

Tree – Root
Parent – Child
Shortcut Trust
External Trust
Forest Trust
Realm Trust

1. Tree - Root:-

A Tree – Root trust is:
Implicitly created,
Transitive
Two Way

2. Parent – Child

A Parent – Child trust is:
Implicitly created
Transitive
Two Way

3. Shortcut Trust:

Explicitly created
Transitive,
One Way or Two Way

This is used to improve user logon times between 2 domains in the same forest

4. External Trust:

Explicitly created
Non Transitive,
One Way or Two Way

This is created between domains in the different forests or
Between Windows Server 2003 domain and a domain running under Windows NT or earlier versions of Windows
This is used when users require access to resources in Windows NT domain or with separate forest.

5. Forest Trust:-

Explicitly created,
Transitive between 2 forests only ; Non Transitive across 3 or more forests,
OneWay or Two Way

6. Realm Trust:-

Explicitly created,
Non-transitive,
One Way or Two Way

This trust is created between a non-Windows Kerberos realm and a Windows Server 2003 domain