NANOG/IEPG/ISOC's current role

Curtis Villamizar curtis at
Thu Apr 4 03:17:16 UTC 1996

In message <199604030045.QAA03247 at>, Paul Ferguson writes:
> At 04:26 PM 4/2/96 -0800, Michael Dillon wrote:
> >On Tue, 2 Apr 1996, Curtis Villamizar wrote:
> >
> >> If the providers were to relax the requirements to renumber when
> >> moving to another provider or when dual homing, the problem of the 
> >> TWD would not be growing at its current rate.
> >
> >Hmmm.... ISP has T1 to SPRINT, wants to switch to MCI, SPRINT says, OK
> >you have a choice, either renumber or pay us to route your traffic to MCI 
> >via a private exchange point so we don't have to knock holes in our 
> >aggregate. That way you can use SPRINT's addresses and MCI's T1, but for 
> >a fee.
> And the global routing table grows.
> - paul


Provider X takes on some number of customers N that want prefixes and
think they may later dual home or want to leave the option of changing
providers without renumbering open.  Substitute for X as you see fit.

If provider X insists that small providers or small to medium business
customers must renumber to leave a CIDR aggregate the smaller
organization go off and get "portable" address allocations which put
them in the unaggregatable toxic waste dump (TWD).  If so, they will
also try as hard as they can to get a /19.

Some of the small prefixes go out of business.  Some grow and become
dual homed.  Some switch providers.  Most just don't change.

In either case, TWD allocation or out of a provider aggregate, a dual
homed customer requires an additional prefix (to get routing right).

If a small prefix changes providers and is TWD allocated, they already
have a unique route.  If they were allocated from a large provider
aggregate, one more prefix is needed.  If they were allocated from a
large provider aggregate and are given a generous grace period, some
will renumber quickly, some not at all (continuous requests to extend
the grace period).  Lets assume they are never forced (grace period
extensions are granted).

If the number of small prefixes that resort to the TWD as a result of
strong renumbering policies exceeds the number of small prefixes that
move out of aggregates without eventually renumbering, then there the
strong renumbering policy actually promotes more growth in the routing
table size.

In the short term, the difference may not be all that substantial.
Longer term, if the provider community can cooperate to aggregate
better then many of the extra routes caused by prefixes changing
providers can be aggregated back together over a multple AS
aggregation boundary.

Since you made the comment "And the global routing table grows", do
you feel what I described above is invalid?  If so, what assumptions
are you making differently?  Do you feel people will never renumber if
given a grace period, even if renumbering becomes easier with time?


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