Default-free zone definition
A default-free zone (DFZ) is a part of the internet where routers do not rely on a default route for forwarding packets. In a DFZ, they have a routing table that includes all available routes on the internet. DFZ is typically found in the core of the internet, particularly among Tier 1 internet service providers (ISPs) and major internet backbone networks.
DFZ routing tables
In a typical network setup, routers have a default path when they send traffic to unknown destinations. In a DFZ, routers have a complete routing table with entries for all reachable destinations on the internet. It allows them to make direct routing decisions without relying on a default route. In turn, as the routers work much faster, they can direct traffic and enhance the speed and reliability of internet connections.
To maintain complete and accurate routing tables, DFZs use the Border Gateway protocol for exchanging routing information, but it requires significant resources and expertise. As the internet continues to grow, it becomes significantly more challenging to scale those tables accordingly.