Chapter 8: Routing Pg 252 - 258

BGP
- autonomous system (AS): one or more networks that are governed by a single dynamic routing protocol within that system
        -> do not use IP addresses
        -> they use a globally unique Autonomous System Number (ASN)
        -> originally 16-bit but are now 32-bit broken into two separate 16-bit numbers broken by a dot (.)
        -> AS's communicate using Exterior Gateway Protocol (EGP)
        -> networks with an AS communicate using Interior Gateway Protocols (IGP)
- Border Gateway Protocol (BGP - 4): connects all of the Autonomous Systems on the internet
        -> BGP routers are manually configured
        -> supports policies for limiting which and how other routers may access an ISP
       
Link State
- link state dynamic routing protocol 
        -> OSPF
        -> IS-IS

OSPF
- Open Shortest Path First (OSPF)
        -> used on internal networks
        -> converges faster and more efficiently than RIP 
        -> not often found on home routers
- link state advertisements (LSAs) are sent out by OSPF capable routers
        -> forwarded to every OSPF router in the network
- every router in the network is assigned an area ID 
- designated router (DR): relays information to all of the other routers in the area
- backdup desginated router (BDR): used in the event the DR is not available
        -> the DR and BDR compete to become the DR during the inital LSA packet exchange
- flooding when a new router initially starts and sends out a plethora of LSAs
- cost of an OSPF is based off of 100,000,000/bandwidth in bps
         -> the faster the bandwidth the lower the cost
- scales to large networks and is supported by nearly all routers
- OSPF corrects link failures and creates convergence almost immediately