New Solutions for Scaling the Internet Address Space

As we enter the 21st century, the problems of IPv4 address shortages

and expanding Internet routing tables are still with us. The good news

is that CIDR is working. The bad news is that recent growth trends indi 

cate that the number of Internet routes is increasing at an exponential

rate. The Internet must find a way to keep the routing table growth lin 

ear. The IETF is continuing its efforts to develop solutions that will

overcome these problems, enabling the continued growth and scalability

of the Internet. 

Appeal to Return Unused IP Network Prefixes

RFC 1917 requests that the Internet community return unused address

blocks to the Internet Assigned Numbers Authority (IANA) for redistri 

bution. This includes unused network numbers, addresses for networks

that will never be connected to the global Internet for security reasons,

and sites that are using a small percentage of their address space. RFC

1917 also petitions ISPs to return unused network prefixes that are out 

side of their assigned address blocks. 

Address Allocation for Private Internets

RFC 1918 requests that organizations use the private Internet address

space for hosts that require IP connectivity within their enterprise net 

work, but do not require external connections to the global Internet.

The IANA has reserved the following three address blocks for private

Internets: 

  10.0.0.0   10.255.255.255 (10/8 prefix) 

  172.16.0.0   172.31.255.255 (172.16/12 prefix) 

  192.168.0.0   192.168.255.255 (192.168/16 prefix) 

Any organization that elects to use addresses from these reserved blocks

can do so without contacting the IANA or an Internet registry. Since

these addresses are never injected into the global Internet routing sys 

tem, the address space can simultaneously be used by many different

organizations. 

The disadvantage to this addressing scheme is that it requires an organi 

zation to use a Network Address Translator (NAT) for global Internet

access. However, the use of the private address space and a NAT make it

much easier for clients to change their ISP without renumbering or

 punching holes  in a previously aggregated advertisement. A benefit

of this addressing scheme to the Internet is that it reduces the demand

for IP addresses so large organizations may require only a small block of

the globally unique IPv4 address space. 

U N D E R S TA N D I N G   I P   A D D R E S S I N G

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