010 - BGP

1. BGP is path vector protocol
2. BGP message types:
   Open - Used to form peer relationships
   Keepalive - Periodic maintenance of relationships
   Update - Communicates routing information Notification - Communicates an error
3. BGP neighbor states:
   Idle
   Connect - A TCP connection is being attempted
   Active - A TCP connection has failed; the router is waiting to be contacted by its peer
   OpenSent - TCP session established, open message sent
   OpenConfirm - Waiting for a keepalive from the peer Established
4. Path Attributes
   Attribute classes:
   Well-known mandatory attributes must be supported and included
   Well-known discretionary attributes must be supported but may not be included
   Optional transitive attributes don't have to be supported, but must be passed onto peer Optional nontransitive attributes don't have to be supported, and can be ignored
5. BGP Attributes are as follows:
   [1] Weight (16-bit value) - Highest weight is preferred
   [2] Local Preference - Highest preferred
   [3] Router originated from local router - next hop 0.0.0.0
   [4] Shortest AS path
   [5] Lowest origin code ( IGP EGP ?)
   [6] Lowest MED ( Multi Exit Discriminator)
   [7] Choose EBGP route over IBGP route
   [8] Choose router through the nearest IGP neighbor as determined by the lowest IGP metric
   [9] Choose the Oldest route
   [10] Choose a path through the neighbor with the lowest router ID
   [11] Choose a path through the neighbor with the lowest IP address