Default-free zone

In Internet routing, the default-free zone (DFZ) is the collection of all Internet routers that do not require a default route to route a packet to any destination, most commonly at the core of autonomous systems. Conceptually, DFZ routers have a "complete" Border Gateway Protocol table, sometimes referred to as the Internet routing table, global routing table or global BGP table. However, internet routing changes rapidly and the widespread use of route filtering leads to not every router having the same view of all routes. Any routing table created would look different from the perspective of different routers, even if a stable view could be achieved.

Highly connected autonomous systems and routers

The Weekly Routing Reports used by the ISP community come from the Asia-Pacific Network Information Centre (APNIC) router in Tokyo, which is a well-connected router that has as good a view of the Internet as any other single router. For serious routing research, however, routing information will be captured at multiple well-connected sites, including high-traffic ISPs (see the "skitter core") below.

On May 12, 2014, there were 494,105 routes seen by the APNIC router. These came from 46,795 autonomous systems, of which only 172 were transit-only and 35787 were stub/origin-only. 6087 autonomous systems provided some level of transit. By July 2025, this number has increased to around 990 thousand IPv4 routes, and generally surpassed one million in September 2025, although the number of prefixes can vary by many thousands depending on where the router is located, leading to some routers reaching this number earlier or later. Combined with IPv6 routes, the total routing table size has grown to over 1.2 million entries at that time.