CCNP - BGP

Basics

 * The routing protocol of the Internet.
 * Exterior Gateway Protocol (EGP).
 * Connects to neighbors with TCP port 179.
 * Route prefixes and lengths information referred to as Network Layer Reachability Information (NLRI).
 * Uses several Path Attributes (PAs) instead of a single metric.
 * Compares these PAs in a certain order to determine the best route.
 * Corporations recognized with Autonomous System Numbers (ASNs).

Single Homed

 * 1 ISP and 1 link to the ISP.
 * Minimizes the benefit of BGP as there is only one possible route to the Internet.

Dual Homed

 * 1 ISP and 2 or more links to the ISP.

Single Multihomed

 * 2 ISPs and 1 link for each ISP.

Dual Multihomed

 * 2 ISPs and multiple links for each ISP.

ASNs

 * Used to uniquely identify an autonomous system.
 * Has a public and private range.
 * Public: 1 - 65,411
 * Private: 65,412 - 65,535

ASN_Path

 * Describes the list of ASNs a certain route will travel through.
 * Has two main functions:
 * Helps determine the best route.
 * Prevents routing loops.