by Fred Baker, Cisco Systems
In today’s Internet, site multihoming—an edge network configuration that has more than one service provider but does not provide transit communication between them—is relatively common. Per the statistics at www.potaroo.net, almost 40,000 Autonomous Systems are in the network, of which about 5,000 seem to offer transit services to one or more customers. The rest are in terminal positions, possibly meaning three things. They could be access networks, broadband providers offering Internet access to small companies and residential customers; they could be multi-homed edge networks; or they might be networks that intend to multihome at some point in the future. The vast majority, on the order of 75 percent, are multihomed or intend to multihome. That is but one measure; you do not have to use Border Gateway Protocol (BGP) routing to have multiple upstream networks. Current estimates suggest that there is one multihomed entity per 50,000 people worldwide, and one per 18,000 in the United States.
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