The exchange of routing information between ASes is subject to routing policies. Consider the
case of two ASes, X and Y exchanging routing information:
NET1 ...... ASX ASY ....... NET2
ASX knows how to reach a network called NET1. It does not matter whether NET1 is belonging
to ASX or some other AS which exchanges routing information with ASX either directly or indirectly;
we just assume that ASX knows how to direct packets towards NET1. Likewise ASY
knows how to reach NET2.