This document analyzes the state of the Internet domain-based routing system, concentrating on Inter-Domain Routing (IDR) and also considering the relationship between inter-domain and intra-domain routing. The analysis is carried out with respect to RFC 1126 and other IDR requirements and design efforts looking at the routing system as it appeared to be in 2001 with editorial additions reflecting developments up to 2006. It is the companion document to "A Set of Possible Requirements for a Future Routing Architecture" (RFC 5772), which is a discussion of requirements for the future routing architecture, addressing systems developments and future routing protocols. This document summarizes discussions held several years ago by members of the IRTF Routing Research Group (IRTF RRG) and other interested parties. The document is published with the support of the IRTF RRG as a record of the work completed at that time, but with the understanding that it does not necessarily represent either the latest technical understanding or the technical consensus of the research group at the date of publication.