Default-free zone
In Internet routing, the default-free zone (DFZ) is the collection of all Internet autonomous systems (AS) that do not require a default route to route a packet to any destination. 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 ensures that no router has a complete 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
As of 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.[2]
The idea of an "Internet core"
The term "default-free zone" is sometimes confused with an "Internet core" or Internet backbone, but there has been no true "core" since before the Border Gateway Protocol (BGP) was introduced. In pre-BGP days, when the Exterior Gateway Protocol (EGP) was the exterior routing protocol, it indeed could be assumed there was a single Internet core.
That concept, however, has been obsolete for a long time. At best, today's definition of the Internet core is statistical, with the "skitter core" being some number of AS with the greatest traffic according to the
Information at Internet exchange points
Large
Before the current commercial Internet evolved, the NSFNET, which interconnected five US government funded supercomputer centers, could have been considered the high-speed Internet core. Four IXPs supported NSFNET, but these IXPs evolved into a model where commercial traffic could meet there. While it is slightly difficult to point to a precise endpoint, NSF funding for transmission ceased by 1998.
Customer, non-ISP participation in the DFZ
It is common practice, in a
See also
- Multihoming
- IP transit
- Peering
- Route filtering
- 512K Day
References
- ^ "BGP Routing Table Analysis". September 2014. Retrieved 2015-06-13.
- ^ "Routing Table Report 04:00 +10GMT Mon 12 May, 2014". 2014-05-12. Retrieved 2015-06-13.
- ^ "IPv4 and IPv6 AS Core: Visualizing IPv4 and IPv6 Internet Topology at a Macroscopic Scale". Center for Applied Internet Data Analysis. 2014-06-23. Retrieved 2015-06-13.
- ^ Labovitz, Craig; Malan, G. Robert; Jahanian, Farnam (1998). "Origins of Internet Routing Instability" (PDF). Retrieved 2015-06-13.
- .