As per Relevance of the word allocate, we have this rfc below:
Network Working Group V.
Request for Comments: 1338
T.
J.
K.
June 1992
Supernetting: an Address Assignment and Aggregation
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard. Distribution of this memo
unlimited
This memo discusses strategies for address assignment of the
IP address space with a view to conserve the address space and
the explosive growth of routing tables in default-route-free
run by transit routing domain providers
Table of
Acknowledgements ................................................. 2
1. Problem, goal, and motivation ................................ 2
2. Scheme plan .................................................. 3
2.1. Aggregation and its limitations ............................ 3
2.2. Distributed network number allocation ...................... 5
3. Cost-benefit analysis ........................................ 6
3.1. Present allocation figures ................................. 7
3.2. Historic growth rates ...................................... 8
3.3. Detailed analysis .......................................... 8
3.3.1. Benefits of new addressing plan .......................... 9
3.3.2. Growth rate projections .................................. 9
4. Changes to Inter-Domain routing protocols .................... 11
4.1. General semantic changes ................................... 11
4.2. Rules for route advertisement .............................. 11
4.3. How the rules work ......................................... 13
4.4. Responsibility for and configuration of aggregation ........ 14
5. Example of new allocation and routing ........................ 15
5.1. Address allocation ......................................... 15
5.2. Routing advertisements ..................................... 17
6. Transitioning to a long term solution ........................ 18
Fuller, Li, Yu, & Varadhan [Page 1]
RFC 1338 Supernetting June 1992
7. Conclusions .................................................. 18
8. Recommendations .............................................. 18
9. Bibliography ................................................. 19
10. Security Considerations ...................................... 19
11. Authors' Addresses ........................................... 19
The authors wish to express their appreciation to the members of
ROAD group with whom many of the ideas contained in this
were inspired and developed
1. Problem, Goal, and
As the Internet has evolved and grown over in recent years, it
become painfully evident that it is soon to face several
scaling problems. These include
1. Exhaustion of the class-B network address space.
fundamental cause of this problem is the lack of a
class of a size which is appropriate for mid-
organization; class-C, with a maximum of 254
addresses, is too small while class-B, which allows up
65534 addresses, is to large to be widely allocated
2. Growth of routing tables in Internet routers beyond
ability of current software (and people) to
manage
3. Eventual exhaustion of the 32-bit IP address space
It has become clear that the first two of these problems are
to become critical within the next one to three years. This
attempts to deal with these problems by proposing a mechanism to
the growth of the routing table and the need for allocating new
network numbers. It does not attempt to solve the third problem
which is of a more long-term nature, but instead endeavors to
enough of the short to mid-term difficulties to allow the Internet
continue to function efficiently while progress is made on a longer
term solution
The proposed solution is to hierarchically allocate future IP
assignment, by delegating control of segments of the IP address
to the various network service providers
It is proposed that this scheme of allocating IP addresses
undertaken as soon as possible. It is also believed that the
will suffice as a short term strategy, to fill the gap between
Fuller, Li, Yu, & Varadhan [Page 2]
RFC 1338 Supernetting June 1992
and the time when a viable long term plan can be put into place
deployed effectively. It is believed that this scheme would
viable for at least three (3) years, in which time frame, a
long term solution would be expected to be deployed
Note that this plan neither requires nor assumes that
assigned addresses will be reassigned, though if doing so
possible, it would further reduce routing table sizes. It is
that routing technology will be capable of dealing with the
routing table size and with some reasonably-small rate of growth
The emphasis of this plan is on significantly slowing the rate
this growth
This scheme will not affect the deployment of any specific long
plan, and therefore, this document will not discuss any long
plans for routing and address architectures
2. Scheme
There are two basic components of this addressing and routing scheme
one, to distribute the allocation of Internet address space and two
to provide a mechanism for the aggregation of routing information
2.1. Aggregation and its
One major goal of this addressing plan is to allocate
address space in such a manner as to allow aggregation of
information along topological lines. For simple, single-
clients, the allocation of their address space out of a
provider's space will accomplish this automatically - rather
advertise a separate route for each such client, the service
may advertise a single, aggregate, route which describes all of
destinations contained within it. Unfortunately, not all sites
singly-connected to the network, so some loss of ability to
is realized for the non simple cases
There are two situations that cause a loss of aggregation efficiency
o Organizations which are multi-homed. Because multi-
organizations must be advertised into the system by each
their service providers, it is often not feasible to
their routing information into the address space any one
those providers. Note that they still may receive
address allocation out of a service provider's address
(which has other advantages), but their routing
must still be explicitly advertised by most of their
providers (the exception being that if the site's
comes out of its least-preferable service provider, then
Fuller, Li, Yu, & Varadhan [Page 3]
RFC 1338 Supernetting June 1992
service provider need not advertise the explicit route -
longest-match will insure that its aggregated route is used
get to the site on a non-primary basis). For this reason,
routing cost for these organizations will typically be
the same as it is today
o Organizations which move from one service provider to another
This has the effect of "punching a hole" in the aggregation
the original service provider's advertisement. This plan
handle the situation by requiring the newer service
to advertise a specific advertisement for the new client
which is preferred by virtue of being the longest match.
maintain efficiency of aggregation, it is recommended
organizations which do change service providers plan
eventually migrate their address assignments from the
provider's space to that of the new provider. To this end,
is recommended that mechanisms to facilitate such migration
including improved protocols and procedures for dynamic
address assignment, be developed
Note that some aggregation efficiency gain can still be had
multi-homed sites (and, in general, for any site composed
multiple, logical IP network numbers) - by allocating a
block of network numbers to the client (as opposed to multiple
independently represented network numbers) the client's
information may be aggregated into a single (net, mask) pair. Also
since the routing cost associated with assigning a multi-homed
out of a service provider's address space is no greater than
current method of a random allocation by a central authority,
makes sense to allocate all address space out of blocks assigned
service providers
It is also worthwhile to mention that since aggregation may
at multiple levels in the system, it may still be possible
aggregate these anomalous routes at higher levels of
hierarchy may be present. For example, if a site is multi-homed
two NSFNet regional networks both of whom obtain their
space from the NSFNet, then aggregation by the NSFNet of
from the regionals will include all routes to the multi-homed site
Finally, it should also be noted that deployment of the
addressing plan described in this document may (and should)
almost immediately but effective use of the plan to
routing information will require changes to some Inter-
routing protocols. Likewise, deploying the supernet-capable Inter
Domain protocols without deployment of the new address plan
not allow useful aggregation to occur (in other words,
Fuller, Li, Yu, & Varadhan [Page 4]
RFC 1338 Supernetting June 1992
addressing plan and routing protocol changes are both required
supernetting, and its resulting reduction in table growth, to
effective.) Note, however, that during the period of time
deployment of the addressing plan and deployment of the
protocols, the size of routing tables may temporarily grow
rapidly. This must be considered when planning the deployment
the two plans
Note: in the discussion and examples which follow, the network+
notation is used to represent routing destinations. This is
for illustration only and does not require that routing
use this representation in their updates
2.2. Distributed allocation of address
The basic idea of the plan is to allocate one or more blocks
Class-C network numbers to each network service provider
Organizations using the network service provider for
connectivity are allocated bitmask-oriented subsets of
provider's address space as required
Note that in contrast to a previously described scheme
subnetting a class-A network number, this plan should not
difficult host changes to work around domain system limitations -
since each sub-allocated piece of the address space looks like
class-C network number, delegation of authority for the IN
ADDR.ARPA domain works much the same as it does today - there
just be a lot of class-C network numbers whose IN-ADDR.
delegations all point to the same servers (the same will be true
the root delegating a large block of class-Cs to the
provider, unless the delegation just happens to fall on a
boundary). It is also the case that this method of
class-C's is somewhat easier to deploy, since it does not
the ability to split a class-A across a routing domain
(i.e., non-contiguous subnets).
It is also worthy to mention that once Inter-Domain protocols
support classless network destinations are widely deployed,
rules described by the "supernetting" plan generalize to
arbitrary super/subnetting of the remaining class-A and class-
address space (the assumption being that classless Inter-
protocols will either allow for non-contiguous subnets to exist
the system or that all components of a sub-allocated class-A/B
be contained within a single routing domain). This will allow
plan to continue to be used in the event that the class-C space
exhausted before implementation of a long-term solution is
(there may, however, be further implementation
before doing this).
Fuller, Li, Yu, & Varadhan [Page 5]
RFC 1338 Supernetting June 1992
Hierarchical sub-allocation of addresses in this manner
that clients with addresses allocated out of a given
provider are, for routing purposes, part of that service
and will be routed via its infrastructure. This implies
routing information about multi-homed organizations, i.e.,
organizations connected to more than one network service provider
will still need to be known by higher levels in the hierarchy
The advantages of hierarchical assignment in this fashion
a) It is expected to be easier for a relatively small number
service providers to obtain addresses from the
authority, rather than a much larger, and
increasing, number of individual clients. This is not to
considered as a loss of part of the service providers'
space
b) Given the current growth of the Internet, a scalable
delegatable method of future allocation of network numbers
to be achieved
For these reasons, and in the interest of providing a
procedure for obtaining Internet addresses, it is recommended
most, if not all, network numbers be distributed through
providers
3. Cost-benefit
This new method of assigning address through service providers can
put into effect immediately and will, from the start, have
benefit of distributing the currently centralized process
assigning new addresses. Unfortunately, before the benefit
reducing the size of globally-known routing destinations can
achieved, it will be necessary to deploy an Inter-Domain
protocol capable of handling arbitrary network+mask pairs. Only
will it be possible to aggregate individual class-C networks
larger blocks represented by single routing table entries
This means that upon introduction, the new addressing plan will
in and of itself help solve the routing table size problem. Once
new Inter-Domain routing protocol is deployed, however, an
drop in the number of destinations which clients of the new
must carry will occur. A detailed analysis of the magnitude of
expected drop and the permanent reduction in rate of growth is
in the next section
In should also be noted that the present method of flat
allocations imposes a large bureaucratic cost on the central
Fuller, Li, Yu, & Varadhan [Page 6]
RFC 1338 Supernetting June 1992
allocation authority. For scaling reasons unrelated to address
exhaustion or routing table overflow, this should be changed.
the mechanism proposed in this paper will have the happy side
of distributing the address allocation procedure, greatly
the load on the central authority
3.1. Present Allocation
A back-of-the-envelope analysis of "network-contacts.txt
(available from the DDN NIC) indicates that as of 2/25/92, 46
126 class-A network numbers have been allocated (leaving 81)
5467 of 16256 class-B numbers have been allocated, leaving 10789.
Assuming that recent trends continue, the number of
class-B's will continue to double approximately once a year.
this rate of grown, all class-B's will be exhausted within
15 months
Fuller, Li, Yu, & Varadhan [Page 7]
RFC 1338 Supernetting June 1992
3.2. Historic growth
MM/YY ROUTES MM/YY
ADVERTISED
------------------------ -----------------------
Feb-92 4775 Apr-90 1525
Jan-92 4526 Mar-90 1038
Dec-91 4305 Feb-90 997
Nov-91 3751 Jan-90 927
Oct-91 3556 Dec-89 897
Sep-91 3389 Nov-89 837
Aug-91 3258 Oct-89 809
Jul-91 3086 Sep-89 745
Jun-91 2982 Aug-89 650
May-91 2763 Jul-89 603
Apr-91 2622 Jun-89 564
Mar-91 2501 May-89 516
Feb-91 2417 Apr-89 467
Jan-91 2338 Mar-89 410
Dec-90 2190 Feb-89 384
Nov-90 2125 Jan-89 346
Oct-90 2063 Dec-88 334
Sep-90 1988 Nov-88 313
Aug-90 1894 Oct-88 291
Jul-90 1727 Sep-88 244
Jun-90 1639 Aug-88 217
May-90 1580 Jul-88 173
Table I : Growth in routing table size, total
Source for the routing table size data is
3.3. Detailed
There is no technical cost and minimal administrative
associated with deployment of the new address assignment plan.
administrative cost is basically that of convincing the NIC,
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
and the IANA) will be greatly decreased by the deployment of
plan. To take advantage of aggregation of routing information
however, it is necessary that the capability to represent
as arbitrary network+mask fields (as opposed to the
class-A/B/C distinction) be added to the common Internet inter
domain routing protocol(s).
Fuller, Li, Yu, & Varadhan [Page 8]
RFC 1338 Supernetting June 1992
3.3.1. Benefits of the new addressing
There are two benefits to be had by deploying this plan
o The current problem with depletion of the available class-
address space can be ameliorated by assigning more
appropriately sized blocks of class-C's to mid-
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
followed by a significant reduction in the rate growth
routing table size should occur (for default-free routers).
3.3.2. Growth rate
Currently, a default-free routing table (for example, the
tables maintained by the routers in the NSFNET backbone)
approximately 4700 entries. This number reflects the current
of the NSFNET routing database. Historic data shows that
number, on average, has doubled every 10 months between 1988
1991. Assuming that this growth rate is going to persist in
foreseeable future (and there is no reason to assume otherwise),
we expect the number of entries in a default-free routing table
grow to approximately 30000 in two(2) years time. In
following analysis, we assume that the growth of the Internet
been, and will continue to be, exponential
It should be stressed that these projections do not consider
the current shortage of class-B network numbers may increase
number of instances where many class-C's are used rather than
class-B. Using an assumption that new organizations which
obtained class-B's will now obtain somewhere between 4 and 16
class-C's, the rate of routing table growth can conservatively
expected to at least double and probably quadruple. This means
number of entries in a default-free routing table may well
10,000 entries within six months and 20,000 entries in less than
year
Under the proposed plan, growth of the routing table in
default-free router is greatly reduced since most new
assignment will come from one of the large blocks allocated to
service providers. For the sake of this analysis, we
prompt implementation of this proposal and deployment of
revised routing protocols. We make the initial assumption that
initial block given to a provider is sufficient to satisfy
needs for two years
Fuller, Li, Yu, & Varadhan [Page 9]
RFC 1338 Supernetting June 1992
Since under this plan, multi-homed networks must continue to
explicitly advertised throughout the system (according to Rule#1
described in section 4.2), the number multi-homed routes
expected to be the dominant factor in future growth of
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
organization's network is comprised of one or more
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
advertisement may be possible. This means that the number
routes advertised within the Internet for multi-homed networks
be approximated as the total number of multi-homed organizations
Assuming that the number of multi-homed organization will
every year (which may be a over-estimation, given that
connection costs money), the number of routes for multi-
networks would be expected to grow to approximately 800 in
years
If we further assume that there are approximately 100
providers, then each service provider will also need to
its block of addresses. However, due to aggregation,
advertisements will be reduced to only 100 additional routes.
assume that after the initial two years, new service
combined with additional requests from existing providers
require an additional 50 routes per year. Thus, the total is 4700
+ 800 + 150 = 5650. This represents an annual grown rate
approximately 6%. This is in clear contrast to the current
growth of 150%. This analysis also assumes an
deployment of this plan with full compliance. Note that
analysis assumes only a single level of route aggregation in
current Internet - intelligent address allocation
significantly improve this
Clearly, this is not a very conservative assumption in
Internet environment nor can 100% adoption of this proposal
expected. Still, with only a 90% participation in this proposal
service providers, at the end of the target three years,
routing table size will be "only" 4700 + 800 + 145 + 7500 = 13145
routes -- without any action, the routing table will grow
approximately 75000 routes during that time period
Fuller, Li, Yu, & Varadhan [Page 10]
RFC 1338 Supernetting June 1992
4. Changes to Inter-Domain routing
In order to support supernetting efficiently, it is clear that
changes will need to be made to both routing protocols themselves
to the way in which routing information is interpreted. In the
of "new" inter-domain protocols, the actual protocol syntax
should be relatively minor. This mechanism will not work with
inter-domain protocols such as EGP2; the only ways to
with old systems using such protocols are either to use
mechanisms for providing "default" routes or b) require that
routers talking to old routers "explode" supernet information
individual network numbers. Since the first of these is
while the latter is cumbersome (at best -- consider the
requirements it imposes on the receiver of the exploded information),
it is recommended that the first approach be used -- that
systems to continue to the mechanisms they currently employ
default handling
Note that a basic assumption of this plan is that those
which need to import "supernet" information into their
systems must run IGPs (such as OSPF[RFC1267]) which support
routes. Systems running older IGPs may still advertise and
"supernet" information, but they will not be able to propagate
information through their routing domains
4.1. Protocol-independent semantic
There are two fundamental changes which must be applied to Inter
Domain routing protocols in order for this plan to work. First,
concept of network "class" needs to be deprecated - this plan
that routing destinations are represented by network+mask pairs
that routing is done on a longest-match basis (i.e., for a
destination which matches multiple network+mask pairs, the match
the longest mask is used). Second, current Inter-Domain
generally do not support the concept of route aggregation, so the
semantics need to be implemented mechanisms that routers use
interpret routing information returned by the Inter-Domain protocols
In particular, when doing aggregation, dealing with multi-homed
or destinations which change service providers is difficult
Fortunately, it is possible to define several fairly simple rules
dealing with such cases
4.2. Rules for route
1. Routing to all destinations must be done on a longest-
basis only. This implies that destinations which are multi
homed relative to a routing domain must always be
announced into that routing domain - they cannot be
Fuller, Li, Yu, & Varadhan [Page 11]
RFC 1338 Supernetting June 1992
(this makes intuitive sense - if a network is multi-homed,
of its paths into a routing domain which is "higher" in
hierarchy of networks must be known to the "higher" network).
2. A routing domain which performs summarization of
routes must discard packets which match the summarization
do not match any of the explicit routes which makes up
summarization. This is necessary to prevent routing loops
the presence of less-specific information (such as a
route). Implementation note - one simple way to
this rule would be for the border router to maintain a "sink
route for each of its aggregations. By the rule of
match, this would cause all traffic destined to components
the aggregation which are not explicitly known to
discarded
Note that during failures, partial routing of traffic to a site
takes its address space from one service provider but which
actually reachable only through another (i.e., the case of a
which has change service providers) may occur because such
will be routed along the path advertised by the aggregated route
Rule #2 will prevent any real problem from occurring by forcing
traffic to be discarded by the advertiser of the aggregated route
but the output of "traceroute" and other similar tools will
that a problem exists within the service provider advertising
aggregate, which may be confusing to network operators (see
example in section 5.2 for details). Solutions to this problem
to be challenging and not likely to be implementable by
Inter-Domain protocols within the time-frame suggested by
document. This decision may need to be revisited as Inter-
protocols evolve
An implementation following these rules should also make
implementation be generalized, so that arbitrary network number
mask are accepted for all routing destinations. The only
constraint is that the mask must be left contiguous. Note that
degenerate route 0.0.0.0 mask 0.0.0.0 is used as a default route
MUST be accepted by all implementations. Further, to protect
accidental advertisements of this route via the inter-
protocol, this route should never be advertised unless there
specific configuration information indicating to do so
Fuller, Li, Yu, & Varadhan [Page 12]
RFC 1338 Supernetting June 1992
Systems which process route announcements must also be able to
that information which they receive is correct. Thus,
of this plan which filter route advertisements must also allow
in the filter elements. To simplify administration, it would
useful if filter elements automatically allowed more specific
numbers and masks to pass in filter elements given for a more
mask. Thus, filter elements which looked like
accept 128.32.0.0
accept 128.120.0.0
accept 134.139.0.0
accept 36.0.0.0
would look something like
accept 128.32.0.0 255.255.0.0
accept 128.120.0.0 255.255.0.0
accept 134.139.0.0 255.255.0.0
deny 36.2.0.0 255.255.0.0
accept 36.0.0.0 255.0.0.0
This is merely making explicit the network mask which was implied
the class-A/B/C classification of network numbers
4.3. How the rules
Rule #1 guarantees that the routing algorithm used is
across implementations and consistent with other routing protocols
such as OSPF. Multi-homed networks are always explicitly
by every service provider through which they are routed even if
are a specific subset of one service provider's aggregate (if
are not, they clearly must be explicitly advertised). It may seem
if the "primary" service provider could advertise the multi-
site implicitly as part of its aggregate, but the assumption
longest-match routing is always done causes this not to work
Rule #2 guarantees that no routing loops form due to aggregation
Consider a mid-level network which has been allocated the 2048
class-C networks starting with 192.24.0.0 (see the example in
5 for more on this). The mid-level advertises to a "backbone
192.24.0.0/255.248.0.0. Assume that the "backbone", in turn, has
allocated the block of networks 192.0.0.0/255.0.0.0. The
will then advertise this aggregate route to the mid-level. Now,
the mid-level loses internal connectivity to the
192.24.1.0/255.255.255.0 (which is part of its aggregate),
from the "backbone" to the mid-level to destination 192.24.1.1
follow the mid-level's advertised route. When that traffic gets
the mid-level, however, the mid-level *must not* follow the
Fuller, Li, Yu, & Varadhan [Page 13]
RFC 1338 Supernetting June 1992
192.0.0.0/255.0.0.0 it learned from the backbone, since that
result in a routing loop. Rule #2 says that the mid-level may
follow a less-specific route for a destination which matches one
its own aggregated routes. Note that handling of the "default"
(0.0.0.0/0.0.0.0) is a special case of this rule - a network must
follow the default to destinations which are part of one of it'
aggregated advertisements
4.4. Responsibility for and configuration of
The AS which owns a range of addresses has the sole authority
aggregation of its address space. In the usual case, the AS
install manual configuration commands in its border routers
aggregate some portion of its address space. As AS can also
aggregation authority to another AS. In this case, aggregation
done in the other AS by one of its border routers
When an inter-domain border router performs route aggregation,
needs to know the range of the block of IP addresses to
aggregated. The basic principle is that it should aggregate as
as possible but not to aggregate those routes which cannot be
as part of a single unit due to multi-homing, policy, or
constraints
One mechanism is to do aggregation solely based on
learned routing information. This has the danger of not specifying
precise enough range since when a route is not present, it is
always possible to distinguish whether it is temporarily
or that it does not belong in the aggregate. Purely dynamic
also does not allow the flexibility of defining what to
within a range. The other mechanism is to do all aggregation based
ranges of blocks of IP addresses preconfigured in the router. It
recommended that preconfiguration be used, since it more flexible
allows precise specification of the range of destinations
aggregate
Preconfiguration does require some manually-maintained
information, but not excessively more so than what
administrators already maintain today. As an addition to the
of information that must be typed in and maintained by a human
preconfiguration is just a line or two defining the range of
block of IP addresses to aggregate. In terms of gathering
information, if the advertising router is doing the aggregation,
administrator knows the information because the aggregation
are assigned to its domain. If the receiving domain has been
the authority to and task of performing aggregation, the
would be known as part of the agreement to delegate aggregation
Given that it is common practice that a network administrator
Fuller, Li, Yu, & Varadhan [Page 14]
RFC 1338 Supernetting June 1992
from its neighbor which routes it should be willing to accept
preconfiguration of aggregation information does not
additional administrative overhead
5. Example of new allocation and
5.1. Address
Consider the block of 2048 class-C network numbers beginning
192.24.0.0 (0xC0180000 and ending with 192.31.255.0 (0xC01FFF00)
allocated to a single network provider, "RA". A "supernetted"
to this block of network numbers would be described as 192.24.0.0
with mask of 255.248.0.0 (0xFFF80000).
Assume this service provider connects six clients in the
order (significant because it demonstrates how temporary "holes"
form in the service provider's address space):
"C1" requiring fewer than 2048 addresses (8 class-C networks
"C2" requiring fewer than 4096 addresses (16 class-C networks
"C3" requiring fewer than 1024 addresses (4 class-C networks
"C4" requiring fewer than 1024 addresses (4 class-C networks
"C5" requiring fewer than 512 addresses (2 class-C networks
"C6" requiring fewer than 512 addresses (2 class-C networks
In all cases, the number of IP addresses "required" by each client
assumed to allow for significant growth. The service
allocates its address space as follows
C1: allocate 192.24.0 through 192.24.7. This block of networks
described by the "supernet" route 192.24.0.0 and
255.255.248.0
C2: allocate 192.24.16 through 192.24.31. This block is
by the route 192.24.16.0, mask 255.255.240.0
C3: allocate 192.24.8 through 192.24.11. This block is
by the route 192.24.8.0, mask 255.255.252.0
C4: allocate 192.24.12 through 192.24.15. This block is
by the route 192.24.12.0, mask 255.255.252.0
C5: allocate 192.24.32 and 192.24.33. This block is described
Fuller, Li, Yu, & Varadhan [Page 15]
RFC 1338 Supernetting June 1992
the route 192.24.32.0, mask 255.255.254.0
C6: allocate 192.24.34 and 192.24.35. This block is described
the route 192.24.34.0, mask 255.255.254.0
Note that if the network provider uses an IGP which can
classless networks, he can (but doesn't have to)
"supernetting" at the point where he connects to his clients
therefore only maintain six distinct routes for the 36 class-
network numbers. If not, explicit routes to all 36 class-C
will have to be carried by the IGP
To make this example more realistic, assume that C4 and C5 are multi
homed through some other service provider, "RB". Further assume
existence of a client "C7" which was originally connected to "RB"
has moved to "RA". For this reason, it has a block of network
which are allocated out "RB"'s block of (the next) 2048 class-
network numbers
C7: allocate 192.32.0 through 192.32.15. This block is
by the route 192.32.0, mask 255.255.240.0
For the multi-homed clients, we will assume that C4 is advertised
primary via "RA" and secondary via "RB"; C5 is primary via "RB"
secondary via "RA". To connect this mess together, we will
that "RA" and "RB" are connected via some common "backbone"
"BB".
Graphically, this simple topology looks something like this
Fuller, Li, Yu, & Varadhan [Page 16]
RFC 1338 Supernetting June 1992
C
192.24.0.0 -- 192.24.7.0 \ _ 192.32.0.0 - 192.32.15.0
192.24.0.0/255.255.248.0 \ / 192.32.0.0/255.255.240.0
\ / C
C2 +----+ +----+
192.24.16.0 - 192.24.31.0 \| | | |
192.24.16.0/255.255.240.0 | | _ 192.24.12.0 - 192.24.15.0 _ | |
| | / 192.24.12.0/255.255.252.0 \ | |
C3 -| |/ C4 \| |
192.24.8.0 - 192.24.11.0 | RA | | RB |
192.24.8.0/255.255.252.0 | |___ 192.24.32.0 - 192.24.33.0 ___| |
/| | 192.24.32.0/255.255.254.0 | |
C6 | | C5 | |
192.24.34.0 - 192.24.35.0 | | | |
192.24.34.0/255.255.254.0 | | | |
+----+ +----+
\\ \\
192.24.12.0/255.255.252.0 (C4) || 192.32.12.0/255.255.252.0 (C4) ||
192.24.32.0/255.255.254.0 (C5) || 192.32.32.0/255.255.192.0 (C5) ||
192.32.0.0/255.255.240.0 (C7) || 192.32.0.0/255.248.0.0 (RB) ||
192.24.0.0/255.248.0.0 (RA) || ||
VV
+--------------- BACKBONE PEER BB ---------------+
5.2. Routing
To follow rule #1, RA will need to advertise the block of
that it was given and C7. Since C4 and C5 are multi-homed, they
also be advertised
Advertisements from "RA" to "BB" will be
192.24.12.0/255.255.252.0 primary (advertises C4)
192.24.32.0/255.255.254.0 secondary (advertises C5)
192.32.0.0/255.255.240.0 primary (advertises C7)
192.24.0.0/255.248.0.0 primary (advertises remainder of RA
For RB, the advertisements must also include C4 and C5 as well
it's block of addresses. Further, RB may advertise that C7
unreachable
Advertisements from "RB" to "BB" will be
192.24.12.0/255.255.252.0 secondary (advertises C4)
192.24.32.0/255.255.254.0 primary (advertises C5)
192.32.0.0/255.248.0.0 primary (advertises remainder of RB
Fuller, Li, Yu, & Varadhan [Page 17]
RFC 1338 Supernetting June 1992
To illustrate the problem alluded to by the "note" in section 4.2,
consider what happens if RA loses connectivity to C7 (the
which is allocated out of RB's space). In a stateful protocol,
will announce to BB that 192.32.0.0/255.255.240.0 has
unreachable. Now, when BB flushes this information out of its
table, any future traffic sent through it for this destination
be forwarded to RB (where it will be dropped according to Rule #2)
virtue of RB's less specific match 192.32.0.0/255.248.0.0.
this does not cause an operational problem (C7 is unreachable in
case), it does create some extra traffic across "BB" (and may
prove confusing to a network manager debugging the outage
"traceroute"). A mechanism to cache such unreachability
would help here, but is beyond the scope of this document (such
mechanism is also not implementable in the near-term).
6. Transitioning to a long term
This solution does not change the Internet routing and
architectures. Hence, transitioning to a more long term solution
not affected by the deployment of this plan
7.
We are all aware of the growth in routing complexity, and the
increase in allocation of network numbers. Given the rate at
this growth is being observed, we expect to run out in a few
years
If the inter-domain routing protocol supports carrying network
with associated masks, all of the major concerns demonstrated in
paper would be eliminated
One of the influential factors which permits maximal exploitation
the advantages of this plan is the number of people who agree to
it. It is hoped that having the IAB and the Internet society
this plan would go a long way in the wide deployment, and
benefit of this plan
If service providers start charging networks for advertising
numbers, this would be a very great incentive to share the
space, and hence the associated costs of advertising routes
service providers
8.
The NIC should begin to hand out large blocks of class-C addresses
network service providers. Each block must fall on bit
and should be large enough to serve the provider for two years
Fuller, Li, Yu, & Varadhan [Page 18]
RFC 1338 Supernetting June 1992
Further, the NIC should distribute very large blocks to
and national network service organizations to allow additional
of aggregation to take place at the major backbone networks
Service providers will further allocate power-of-two blocks
class-C addresses from their address space to their subscribers
All organizations, including those which are multi-homed,
obtain address space from their provider (or one of their providers
in the case of the multi-homed). These blocks should also fall
bit boundaries to permit easy route aggregation
To allow effective use of this new addressing plan to
propagated routing information, appropriate IETF WGs will specify
modifications needed to Inter-Domain routing protocols
Implementation and deployment of these modifications should occur
quickly as possible
9.
[RFC1247] Moy, J, "The OSPF Specification Version 2", January 1991.
10. Security
Security issues are not discussed in this memo
11. Authors'
Vince
Pine Hall 115
Stanford, CA, 94305-4122
email: vaf@Stanford.
Tony
cisco Systems, Inc
1525 O'Brien
Menlo Park, CA 94025
email: tli@cisco.
Jessica (Jie Yun)
Merit Network, Inc
1071 Beal Ave
Ann Arbor, MI 48109
email: jyy@merit.
Fuller, Li, Yu, & Varadhan [Page 19]
RFC 1338 Supernetting June 1992
Kannan
Internet Engineer,
1224, Kinnear Road
Columbus, OH 43212
email: kannan@oar.
Fuller, Li, Yu, & Varadhan [Page 20]
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
RFC documents can be found at I.E.T.F.
Relevance System Copyright © 2002 Spectrum WorldResearch
other technical nosh by ServerMasters Corporation
collaboration of BobX
