/19 addresses and redundancy

Tue Nov 11 13:34:10 UTC 1997

Phil Howard <phil at charon.milepost.com> writes:

> Route filtering is not the end of the world.

Wow.  Times have changed.

> You also need to make sure that the ISPs do not filter routes for parts
> of their own blocks coming in from other peers.  If ISP-A did such filtering,
> then their own customers will find you unreachable, as well as those in ISP-C
> if ISP-C sends traffic for you into ISP-A.
> 
> I know of no ISPs doing such a thing

Sprintlink did at one point.  It's a really good idea to do
this in general because it mitigates the disconnectivity
customers assigned prefixes out of one's address blocks
will suffer if and when someone accidentally(?) announces
subnet of those blocks.

Inbound filters can be adjusted, you know.  Unfortunately
the people who have inbound filters have never figured out
that they should make this a service that they charge for.

However, since inbound announcement filtering is a game
anyone can play, I recommend people consider the
implications of fee-based filter updating and how it can
effect their routing whether or not they are the ones
doing the inbound filtering.

Connectivity = bidirectional bandwidth + bidirectional reachability.

Connectivity = value.

	Sean.