Tier 1 Network - Routing

Routing

Internet traffic between any two tier 1 networks is critically dependent on the peering relationship of the partners, because a tier 1 network does not have any alternate transit paths. If two tier 1 networks arrive at an impasse and discontinue peering with each other (usually in a unilateral decision), single-homed customers of each network will not be able to reach the customers of other networks. This effectively partitions the Internet and traffic between certain parts of the Internet is interrupted. This has happened several times during the history of the Internet. Those portions of the Internet typically remain partitioned until one side purchases transit, or until the collective pain of the outage or threat of litigation motivates the two networks to resume voluntary peering.

Lower tier ISPs and their customers may be unaffected by these partitions because they may have redundant interconnections with more than one tier-1 provider.