Re: [RRG] Topology that follows addressing

[Tony Li <tli@cisco.com>]

On Nov 22, 2007, at 4:16 AM, HeinerHummel@aol.com 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