Peering

The AS are considered “neighbors”, or “peers” of one another.  They exchange routing info with each other.  Since the number of routes is so large, agreements are drawn up and coded into the routers – called “Peering Agreements”.  The large ISP’s all have very permissive peering agreements with each other.  However, smaller ISP’s often have difficulties, because the large ISP’s – which are critical conduits for their traffic – hesitate to allow new peering agreements, particularly with these small ISP’s.