I think the taxonomy is probably my fault. At least, I thought I invented it when I wrote
http://ftp.isc.org/isc/pubs/tn/isc-tn-2003-1.txt
the pertinent text of which is this:
Two classes of node are described in this document:
Global Nodes advertise their service supernets such that they are
propagated globally through the routing system (i.e. they
advertise them for transit), and hence potentially provide service
for the entire Internet.
Local Nodes advertise their service supernets such that the radius of
propagation in the routing system is limited, and hence provide
service for a contained local catchment area.
Global Nodes provide a baseline degree of proximity to the entire
Internet. Multiple global nodes are deployed to ensure that the
general availability of the service does not rely on the availability
or reachability of a single global node.
Local Nodes provide contained regions of optimisation. Clients within
the catchment area of a local node may have their queries serviced by
a Local Node, rather than one of the Global Nodes.
The operational considerations that you mention would have been great for me to think about when I wrote that text (i.e. it's the intention of the originator of the route that's important, not the practical limit to propagation of the route due to the policies of other networks).
We did a slightly better job in RFC 4768 (e.g. "in such a way", "potentially"):
Local-Scope Anycast: reachability information for the anycast
Service Address is propagated through a routing system in such a
way that a particular anycast node is only visible to a subset of
the whole routing system.
Local Node: an Anycast Node providing service using a Local-Scope
Anycast Address.
Global-Scope Anycast: reachability information for the anycast
Service Address is propagated through a routing system in such a
way that a particular anycast node is potentially visible to the
whole routing system.
Global Node: an Anycast Node providing service using a Global-Scope
Anycast Address.
Joe
