RFC 1519 CIDR Address Strategy September 1993
3.2 Historic growth rates
MM/YY ROUTES MM/YY ROUTES
ADVERTISED ADVERTISED
------------------------ -----------------------
Dec-92 8561 Sep-90 1988
Nov-92 7854 Aug-90 1894
Oct-92 7354 Jul-90 1727
Sep-92 6640 Jun-90 1639
Aug-92 6385 May-90 1580
Jul-92 6031 Apr-90 1525
Jun-92 5739 Mar-90 1038
May-92 5515 Feb-90 997
Apr-92 5291 Jan-90 927
Mar-92 4976 Dec-89 897
Feb-92 4740 Nov-89 837
Jan-92 4526 Oct-89 809
Dec-91 4305 Sep-89 745
Nov-91 3751 Aug-89 650
Oct-91 3556 Jul-89 603
Sep-91 3389 Jun-89 564
Aug-91 3258 May-89 516
Jul-91 3086 Apr-89 467
Jun-91 2982 Mar-89 410
May-91 2763 Feb-89 384
Apr-91 2622 Jan-89 346
Mar-91 2501 Dec-88 334
Feb-91 2417 Nov-88 313
Jan-91 2338 Oct-88 291
Dec-90 2190 Sep-88 244
Nov-90 2125 Aug-88 217
Oct-90 2063 Jul-88 173
Table I : Growth in routing table size, total numbers
Source for the routing table size data is MERIT
3.3 Detailed Analysis
There is a small technical cost and minimal administrative cost
associated with deployment of the new address assignment plan. The
administrative cost is basically that of convincing the NIC, the
IANA, and the network service providers to agree to this plan, which
is not expected to be too difficult. In addition, administrative
cost for the central numbering authorities (the NIC and the IANA)
will be greatly decreased by the deployment of this plan. To take
advantage of aggregation of routing information, however, it is
necessary that the capability to represent routes as arbitrary
network and mask fields (as opposed to the current class A/B/C
Fuller, Li, Yu & Varadhan [Page 8]
RFC 1519 CIDR Address Strategy September 1993
distinction) be added to the common Internet inter-domain routing
protocol(s). Thus, the technical cost is in the implementation of
classless interdomain routing protocols.
3.3.1 Benefits of the new addressing plan
There are two benefits to be had by deploying this plan:
o The current problem with depletion of the available class B
address space can be ameliorated by assigning more-
appropriately sized blocks of class C's to mid-sized
organizations (in the 200-4000 host range).
o When the improved inter-domain routing protocol is deployed,
an immediate decrease in the number routing table entries
should occur, followed by a significant reduction in the rate
growth of routing table size (for default-free routers).
3.3.2 Growth rate projections
As of Jan '92, a default-free routing table (for example, the routing
tables maintained by the routers in the NSFNET backbone) contained
approximately 4700 entries. This number reflects the current size of
the NSFNET routing database. Historic data shows that this number, on
average, has doubled every 10 months between 1988 and 1991. Assuming
that this growth rate is going to persist in the foreseeable future
(and there is no reason to assume otherwise), we expect the number of
entries in a default-free routing table to grow to approximately
30000 in two years time. In the following analysis, we assume that
the growth of the Internet has been, and will continue to be,
exponential.
It should be stressed that these projections do not consider that the
current shortage of class B network numbers may increase the number
of instances where many class C's are used rather than a class B.
Using an assumption that new organizations which formerly obtained
class B's will now obtain somewhere between 4 and 16 class C's, the
rate of routing table growth can conservatively be expected to at
least double and probably quadruple. This means the number of entries
in a default-free routing table may well exceed 10,000 entries within
six months and 20,000 entries in less than a year.
As of Dec '92, the routing table contains 8500 routes. The original
growth curves would predict over 9400 routes. At this time, it is
not clear if this would indicate a significant change in the rate of
growth.
Under the proposed plan, growth of the routing table in a default-
Fuller, Li, Yu & Varadhan [Page 9]
RFC 1519 CIDR Address Strategy September 1993
free router is greatly reduced since most new address assignment will
come from one of the large blocks allocated to the service providers.
For the sake of this analysis, we assume prompt implementation of
this proposal and deployment of the revised routing protocols. We
make the initial assumption that any initial block given to a
provider is sufficient to satisfy its needs for two years.
Since under this plan, multi-homed networks must continue to be
explicitly advertised throughout the system (according to Rule #1
described in section 4.2), the number multi-homed routes is expected
to be the dominant factor in future growth of routing table size,
once the supernetting plan is applied.
Presently, it is estimated that there are fewer than 100 multi-homed
organizations connected to the Internet. Each such organization's
network is comprised of one or more network numbers. In many cases
(and in all future cases under this plan), the network numbers used
by an organization are consecutive, meaning that aggregation of those
networks during route advertisement may be possible. This means that
the number of routes advertised within the Internet for multi-homed
networks may be approximated as the total number of multi-homed
organizations. Assuming that the number of multi-homed organization
will double every year (which may be a over-estimation, given that
every connection costs money), the number of routes for multi-homed
networks would be expected to grow to approximately 800 in three
years.
If we further assume that there are approximately 100 service
providers, then each service provider will also need to advertise its
block of addresses. However, due to aggregation, these
advertisements will be reduced to only 100 additional routes. We
assume that after the initial two years, new service providers
combined with additional requests from existing providers will
require an additional 50 routes per year. Thus, the total is 4700 +
800 + 150 = 5650. This represents an annual growth rate of
approximately 6%. This is in clear contrast to the current annual
growth of 130%. This analysis also assumes an immediate deployment
of this plan with full compliance. Note that this analysis assumes
only a single level of route aggregation in the current Internet -
intelligent address allocation should significantly improve this.
Clearly, this is not a very conservative assumption in the Internet
environment nor can 100% adoption of this proposal be expected.
Still, with only a 90% participation in this proposal by service
providers, at the end of the target three years, global routing table
size will be "only" 4700 + 800 + 145 + 7500 = 13145 routes -- without
any action, the routing table will grow to approximately 75000 routes
during that time period.
Fuller, Li, Yu & Varadhan [Page 10]