NANOG/IEPG/ISOC's current role

Paul Ferguson pferguso at cisco.com
Thu Apr 4 03:45:12 UTC 1996


At 10:17 PM 4/3/96 -0500, Curtis Villamizar wrote:

>
>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?
>
>Curtis
>

I think that its a fair description.

And honestly, I don't think a substantial percentage of end-networks
will renumber if there are not substantial incentives. If renumbering
becomes less-painful, with time & better tools, perhaps more will
renumber, but again I personally don't foresee a substantial number
doing so without some incentive(s).

The scenario that was previously described by Michael Dillon, I believe,
was one in which a singularly-homed [to provider 'a'] end-network [x]
moved to another provider [provider 'b'] and wanted to take their
provider [a] allocated address(es) with them. This is a case where, if
a larger aggregate is being announced by [a], then a specific component
announced from the [a] CIDR  block would be announced by [b].

Of course, this happens anyway if [x] is dual-homed. I think we can all
agree that the peace-of-mind obtained by [x] in becoming dual-homed is
less than optimal for the Routing Table Watchers (tm).  :-)

This just happens to be a Catch-22 with multihomed end-networks.

- paul




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