Note

A macroscopic visualization of the Internet can be found at the following Web site: http://www.caida.org/analysis/topology/as core network/.

The visualization on the Web site reflects 626,773 IP addresses and 1,007,723 IP links (immediately adjacent addresses in a traceroute-like path) of skitter data. This data was collected from 16 monitors probing approximately

400,000 destinations spread across more than 48,302 (52%) globally routable network prefixes. The Cooperative Association for Internet Data Analysis (CAIDA) then aggregates the network view into a topology of autonomous systems (ASs), each of which approximately maps to an Internet service provider (ISP). CAIDA maps each IP address to the AS responsible for routing it. The abstracted graph consists of 7,624 AS nodes and 25,126 peering sessions. (Geographical location could not be provided for 61 ASs). The resulting graph contains 7,563 ASs (81 percent of all ASs present in the Oregon BGP table of Oct. 15, 2000) and 25,005 peering sessions.

CAIDA is a collaborative undertaking among organizations with a strong interest in keeping primary Internet capacity and usage efficiency in line with demand. Participants come from the commercial, government, and research sectors. CAIDA's members use their organization as a focal point for promoting greater cooperation in the engineering and maintenance of a robust, scalable, global Internet infrastructure. Cisco Systems is a CAIDA sponsor. CAIDA provides the world with a neutral framework to support cooperative technical endeavors that have the potential to be critical in meeting the demands of an exponentially growing system of networks.

BGP is classified as a path-vector routing protocol. A path vector routing protocol is used to select a path across the network. Path vector protocols are similar to distance vector routing protocols. The primary difference between path and distance vector routing protocols is that distance vector routing protocols use hop count to calculate the best path to a destination, whereas path vector routing protocols advertise the reachable destinations to their neighbors. The border router (BR) advertises these destinations, as well as the attributes of the path to the destination. These path vector attributes include the number of hops and the administrative distance of each hop. Interior (IBGP-based) learned routes are given more preference than those learned from an Exterior BGP (EBGP) advertisement.

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