BGP (TCP-179)
4 Message types: Open, Keep Alive, Update, Notify
6 Protocol states: Idle, Connect, Active, OpenSent, OpenConfirm, Established
Many filters and prioritization
eBGP (BGP) - happens only between Autonomous Systems (AS - group of routers run by an organization)
iBGP - happens only in the same Autonomous System
Decision making:
More specific always wins
Weight (Cisco)
Local preference
Preferred from IGP
Shortest AS Path
Better origin
Preferred MED
EBGP > confedEBGP > iBGP
Preferred shortest path to eBGP next hop
Consider BGP multi-path
Preferred lowest BGP router ID