On Nov 22, 2007, at 4:16 AM, [EMAIL PROTECTED] wrote:
>But then
>there's the traditional argument against geographic aggregation: how
>do you avoid ISPs having to carry traffic for free? In other words:
>who announces the aggregates to the rest of the world?
You mean to the rest of this geo-patch (remember: no worldwide
routing churn! ) ! Well just like it is done in OSPF. Hereby,
across any two adjacent ISPs, aggregates shall be announced :
The representative node from ISP A which has a loose=hierarchical
link to some representative node from ISP B shall indeed announce
not only his own reachability info, but also that one of all its
surrounding ISP-A- nodes, which are closer to it than to any other
representative node.
I'm pretty sure I don't understand that explanation.
Advertising all of ISP A's prefix isn't the issue at all. The real
question is: what happens at the geo-patch abstraction (action)
boundary? Where is that boundary? Who is responsible for traffic
arriving into the geo-patch? What happens if the topology within the
geo-patch is internally disconnected?
The traditional explanation is that there must be regulations
requiring an interconnect for the geo-patch and all providers must
connect to that interconnect. The alternative is that providers with
links outside of the geo-patch end up receiving traffic destined for
other providers and end up providing free transit.
More generally, if the entry point at an abstraction action boundary
is not directly connected to all of the sub-abstractions, then you
have a situation where traffic must traverse a sub-abstraction, which
will violate commercial constraints. Thus, the abstraction action
boundary must be located where there is common (or free) connectivity
to all of the sub-abstractions. You can conceivably shift the
abstraction action boundary away from the abstraction naming boundary
to help with this (i.e., do proxy aggregation), but how is this
maintained in the face of changing topology and across hierarchical
levels?
The OSPF assumption that all routers are willing to carry all traffic
simply doesn't hold in the inter-domain routing arena.
Tony
