Internet inter-AS routing: BGP
Suppose: gateway X send its path to peer gateway W
W may or may not select path offered by X
- cost, policy (don’t route via competitors AS), loop prevention reasons.
If W selects path advertised by X, then:
Path (W,Z) = w, Path (X,Z)
Note: X can control incoming traffic by controling its route advertisements to peers:
- e.g., don’t want to route traffic from Z -> don’t advertise any routes to Z