/19 addresses and redundancy

Sean M. Doran writes...

[re: inbound filtering]

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.

Good point.

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.

How easy is this to do. How many filters would a company like
MCI/WorldCom have to place in each peer router?

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.

Should the charge be for adding the filter (deny) or for deleting
it (permit)?

If the provider defaults to deny, then for a customer to request
a permit on their prefix means adding a filter to the router.
If the provider defaults to permit, then a customer wanting a
deny would obviously mean adding a filter.

Once a provider starts charging for the service under one policy,
that means that one set of customers pay the fee and the others
do not. But if the provider decides to change the default, then
it reverses the customer sets of who pays and who does not.

One business model would be to choose the default based on the
largest number of customers paying. But that could result in
customers leaving, either due to the extra fee, or due to the
slower operation of the network with so many filters in place.

The other business model would be the reverse, to choose the
default to minimize the number of filters, minimizing the costs
to the customers and maximizing the performance (while retaining
customer preferred route security policy).

I would tend to prefer the latter model. I doubt such charges
could really make or break the bottom line for most businesses.
The tough position would be if the customer preferences went
about 50/50.


I still wish there was an easy way to filter routes on the
basis of allowing N route prefixes per prefix size per AS
where N might well be 1.

Connectivity = bidirectional bandwidth + bidirectional reachability.

Connectivity = value.

How might symmetry fit into that?

Actually, I view it the other way. If someone is announcing routes for one
of our prefixes, connectivity is at least partially broken for that prefix,
and I want to know about it sooner rather than later. If I see an
advertisement for that route in our router, I can tell quickly who I need
to call.

BTW, this has happened to us twice, and both times the offender was a
direct competitor in one of our local markets. Does anybody have any
feel for how often these "accidents" are not accidents?

John Tamplin Traveller Information Services
jat@Traveller.COM 2104 West Ferry Way
205/883-4233x7007 Huntsville, AL 35801