Question

Consider the following network of Autonomous Systems AS1 through AS6, which double as destinations. When AS1 advertises itself to AS2, for example, the AS-path it provides is 〈AS1〉.

AS1────────AS2────────AS3
 │                     :
 │                     :
 │                     :
AS4────────AS5────────AS6

(a). If neither AS3 nor AS6 exports their AS3–AS6 link to their neighbors AS2 and AS5 to the left, what routes will AS2 receive to reach AS5? Specify routes by AS-path.

(b). What routes will AS2 receive to reach AS6?

(c). Suppose AS3 exports to AS2 its link to AS6, but AS6 continues not to export the AS3–AS6 link to AS5. How will AS5 now reach AS3? How will AS2 now reach AS6? Assume that there are no local preferences in use in BGP best-path selection, and that the shortest AS-path wins.

Answer 1