  We propose to raise network domain to the first-class citizen in packet
routing and forwarding. By making domain explicit in packet header, it can be
held responsible for committed services and quality of service. Since the
service is easier to be monitored, verified, and compensated, a new business
model catering for emerging cross-domain, high-value, and performance-sensitive
applications can be fostered. The domain-level routing and forwarding
essentially create a L3.5 in the network protocol stack. We extend IPv6 with
new routing headers to support two types of forwarding approaches. One is based
on the next domain lookup and the other realizes the domain-level source
routing. We describe various design details covering header format, forwarding
behavior, routing protocol, DNS, and OAM. Several use cases are presented to
demonstrate the scheme potential. The design is compatible with today's
Internet architecture and incrementally deployable on existing infrastructure
with only moderate updates needed. We expect the preliminary work can trigger
more discussion and detailed design in the research and Internet standard
communities.
