Default-free Zone - Customer, Non-ISP Participation in The DFZ

Customer, Non-ISP Participation in The DFZ

It's quite common practice, in a multihomed but stub (i.e., non-transit) autonomous system, for the BGP-speaking router(s) to take "full routes" from the various ISPs to which the AS is multihomed. Especially if there is more than one router connected to the same ISP, a common practice, it will receive more routes than are in the DFZ. Here's the reasoning: when you have two routers connected to a major ISP such as Sprint, France Telecom or Qwest, that provider has a number of customer AS connected to it. The optimal route to those customer AS are important to the ISP itself, but also tells one customer AS which specific router has the best path to the other customer. The "full routes", or properly "full routes plus customer routes", coming to a customer router makes that customer router part of the DFZ, but certainly not part of the current concept of the "skitter core".