BGP will use path attributes with each network path.
These path attributes provide control of routing policies within BGP, these path attributes are classified as:
- Optional non-transitive
- Optional transitive
- Well-known discretionary
- Well-known mandatory
Well known attributes must be recognised by all BGP implementations, with mandatory attributes being included with every prefix advertisement. Discretionary attributes might be included with a prefix advertisement.
Optional attributes do not need to be recognised or implemented by all BGP implementations. They can be set in a way that they transfer from AS to AS as they are advertised through the network. These are known as transitive path attributes. Non-transitive attributes do the opposite and do not transfer through the network.