Regional IRs typically assign address blocks on the basis of an
immediate need and projected utilization rate within one year. (If
you are in the ARIN region, it is one year for end user organizations
and three months for ISPs.) Calculate your address space request
accordingly. It is recommended to include the organization chart and
network topology diagram referred to in section I.C, number 3
(above). Note that address space is allocated based on CIDR bit
boundaries (see next section). The registries will need to
understand your network engineering and deployment plans in
significant detail before they can allocate address space.
Therefore, the more detailed information you can provide, the more
likely your request will be processed quickly.
If you obtain address space from your ISP, it is very likely that you
will need to renumber should you decide to change upstream providers
and/or if you grow considerably. As this renumbering may affect your
customers (and their customers, etc.) if they are using dedicated
lines, you should carefully weigh the cost/benefit involved in
obtaining address space from your upstream provider.
If you are singly homed, you should obtain your address space from
your upstream ISP. If you plan on enlarging but remaining singly
homed, you should continue to obtain space this way as it promotes
aggregation. If, however, you plan to be multi-homed as part of your
growth plan, it would make sense to become a member of an appropriate
Regional IR (or, if one exists in your region, a national Network
Information Center (NIC) and obtain a /19 or "provider aggregatable"
The minimum routable block is often a /19, so if you plan on
enlarging, it is better to pay the fees to the Regional IR now and
obtain a /19 block so that you will not have to renumber later. Note
that if you are an ISP in the ARIN region, ARIN has special
requirements before you can do this in terms of the amount of address
space you have previously used, which must be a /21. The current
policy is that you must have used a /19 previously from your upstream
ISP before going to ARIN, or you must be multi-homed and show you
have used a /21 and be willing to renumber and ARIN will issue a /20
from a reserved /19.
As of February 8, 1999, ARIN lowered the minimum allocation size for
IP addresses from a /19 to a /20. ARIN will issue initial
allocations of prefixes no longer than /20. If allocations smaller
than /20 are needed, ISPs and end users should request address space
from their upstream provider. ARIN does not guarantee that addresses
will be globally routable.
APNIC and RIPE NCC do not have these requirements. For APNIC, new
allocations to members will be a /19.
Remember that your upstream provider should route you if you ask
them. You are a customer of the ISP, so if the service is not what
you need you should change ISPs.
IF YOU ARE CONNECTED TO ONLY ONE PROVIDER, AND ARE NOT VERY LARGE
YET, GET AN ADDRESS RANGE FROM YOUR PROVIDER. SKIP THE REST OF THIS
SECTION AND ALL OF SECTION V.
C. What is CIDR?
CIDR stands for Classless Inter-Domain Routing. Historically, IP
addresses were assigned within classes: Class A (8 bits of network
address, 24 bits of host address), Class B (16 bits of network
address, 16 bits of host address), or Class C (24 bits of network
address, 8 bits of host address). With the advent of CIDR, address
space is now allocated and assigned on bit boundaries. Using CIDR
means you are able to assign addresses corresponding with the number
of hosts on the network, thereby conserving address space.
The following table illustrates this:
Addrs Bits Pref Class Mask
1 0 /32 255.255.255.255
2 1 /31 255.255.255.254
4 2 /30 255.255.255.252
8 3 /29 255.255.255.248
16 4 /28 255.255.255.240
32 5 /27 255.255.255.224
64 6 /26 255.255.255.192
128 7 /25 255.255.255.128
256 8 /24 1C 255.255.255.0
512 9 /23 2C 255.255.254.0
1K 10 /22 4C 255.255.252.0
2K 11 /21 8C 255.255.248.0
4K 12 /20 16C 255.255.240.0
8K 13 /19 32C 255.255.224.0
Wenzel, et al. Informational [Page 9]
RFC 2901 Administrative Internet Infrastructure Guide August 2000
Number of addresses available; note that the number of
addressable hosts normally is 2 less than this number because
the host parts with all equal bits (all 0s, all 1s) are
Size of the allocation/assignment in bits of address space.
Length of the prefix covering this address space. This is
sometimes used to indicate the size of an
Size of the address space in terms of class C network numbers.
The network mask defining the routing prefix in dotted quad
D. How do I request and register address space?
You will need to send a database object to the appropriate registry
to request and register address space. The registration databases
are composed of records that are a series of fields separated by one
or more blank lines; each field consists of two parts, the tag and
the value. Do not modify the tags in the templates or errors will
occur. Values for particular fields are specified in the templates;
be careful to enter appropriate information.
The first line of a template denotes the record type. For example,
an IP address template's first line is inetnum, therefore the record
is known as an inetnum object. This first line is also used as the
primary key for the record, therefore if you want to modify the first
field of the record, the only way to do so is to delete the record
entirely and add a new record with the corrected information.
For illustration, here is the RIPE inetnum object.
inetnum: [IP address range that will be assigned]
descr: Network-Name Communications Company, Town
admin-c: NIC-handle of administrative contact
tech-c: NIC-handle of technical contact
country: ISO 3166-country-code