Practical BGP

BGP's Best Path Algorithm

Interior Gateway Protocol Cost

BGP can also take into consideration the cost of reaching the exit point from within the autonomous system (Figure 1.16).

Figure 1.16. Interior Gateway Protocol cost in BGP metrics.

At router C, the two paths advertised from AS 65200, and passed via iBGP through routers A and D, look the same. From C's perspective, the cost of transmitting the packet from the exit point to the final destination is the same, so it only makes sense to take the shortest path to the exit point from the AS. The easiest way to determine the shortest path to the exit point of the AS is to use interior gateway protocol ...