• Background to IP address allocation and management in Europe
• IP-Plus address allocation procedures and policies

Background to IP address allocation and management in Europe

IP addresses are now designated as either Provider Independent (PI) or Provider Aggregable (PA). The term Provider refers to an Internet Service Provider (ISP). PA addresses come from a block of addresses allocated to an ISP for the purpose of Internet connectivity. These 'CIDR' blocks are routed as a single entity within the global Internet, the effect of which is to reduce the size of the Internet routing tables (Routing table size is the most serious performance issue in the Internet today).

PA addresses are not portable from one ISP to another, because this would tend to break up the CIDR blocks and increase the number of routes again. Changing Internet provider to another will usually mean having to renumber host addresses. In other words, PA addresses belong to the ISP, not the Customer.

PI addresses are meant for cases where the customer wants public addresses, but does not connect them to the Internet. PI addresses can be used on the Internet, but there is no guarentee of worldwide connectivity, due to the fact that some large Internet backbone providers impose a minimum number of networks/route, in order to reduce the size of their routing tables. If the number of PI addresses is much smaller than a typical CIDR block, there is a good chance that users of these addresses will not have global connectivity.

More detailed information on PA and PI addresses can be found in the document RIPE-127 produced by RIPE.

IP-Plus address allocation procedures and policies

IP-Plus is an official RIPE Registry. Our 'assignment window' is currently 2: We can assign customers a block of 512 IP addresses from our CIDR blocks without having to make an application to RIPE.

Customers requiring PA addresses from IP-Plus for Internet purposes should complete form RIPE-141 and send it (preferably by email) to implementation@ip-plus.net. Only IP-Plus Internet customers can receive PA addresses from IP-Plus.

An allocation of PA addresses based on the information supplied to IP-Plus by the Customer is only valid as long as the conditions described in the application continue to apply. If conditions change, or if the information in the original application proves to be incorrect, IP-Plus reserves the right to adjust the size of the allocation as appropriate. Also, if the IP-Plus Internet Service ceases, the PA address allocation is void, and the addresses concerned will be re-allocated to other customers. A ex-customer may continue to use IP-Plus PA addresses on the public Internet for a period of 30 days after the IP-Plus service is disconnected. In the case of large blocks of addresses (over 256 addresses) a longer period can be negotiated, up to an absolute maximum of 6 months. These are the durations recommended in RFC 2008.

For assignments of more than 512 PA addresses IP-Plus must make an application to RIPE on behalf of the customer. Typically this application procedure takes several weeks and requires a great deal of supporting design documents from the customer. A complete network design document is required with network diagram and subnet plan.

If an application for more than 512 PA addresses is successful, IP-Plus will typically reserve the addresses in one of the CIDR blocks on behalf of the customer. Initially, 50% of the assigned addresses are made available to the customer, while the remainder reserved and made available as required. If less than 50% of the assigned addresses are used two years after the initial assignment, then IP-Plus reserves the right to re-assign reserved addresses to other customers.

IP-Plus will not normally apply for PI addresses on behalf of an Internet customer. Small ranges of PI addresses do not guarentee global Internet connectivity, and worsen the problem of routing table growth. Large ranges of PI addresses (typically more than 32 C-class networks) are globally routable, but since a network of this size would almost certainly use a firewall with address translation capability the addresses themselves typically do not appear on the Internet, so it is not necessary to use public addresses for the individual host addresses.

IP-Plus Internet Customers cannot use PA addresses from the CIDR blocks of another ISP. However, at the request of the customer PA addresses allocated to another ISP can be used with the IP-Plus service for a period of the 30 days. This re-numbering period can be extended up to a maximum of 6 months with the written permission of the other ISP. (These re-numbering periods are those recommended in RFC 2008)

Currently, customers coming to IP-Plus with pre-existing IP address assignments which are NOT part of another ISP's CIDR block (either PI or unclassified) are able to use these addresses for the IP-Plus Internet Service. However, we must caution such customers that global connectivity is not guarenteed, and we strongly recommend that they either re-number to a range of PA addresses from the IP-Plus CIDR block, or if the number of addresses is too large, that they use address translation technology (NAT).

Note that it is possible to give up PI addresses, or old addresses that were issued before the concepts of PI/PA came into being, to RIPE ( via IP-Plus) and receive an identical range of PA addresses in return.

The size of range assigned to a customer is decided based on the information returned to IP-Plus in form RIPE-141. In general the factors taken into accountare:

• 80% of the addresses should be utilised within the next two years
• No account can be taken of requirements beyond the next two years
• No account can be taken of extra requirements made necessary by obsolete internetworking equipment that cannot employ variable subnets or classless routing.
• Customers who require large numbers of simultaneous Internet sessions (>512) should use address translation and private RFC 1918 IP addresses.

Static IP address assignment to Dial-Up customers. In some cases a service provider may wish to assign each of his dial-up customers a permanent IP address. The alternative is to dynamically assign a (different) address each time a users connects to the service. Because ratio of dial-up customers to dial-up ports is typically very high, the static assignment techniques uses far more IP addresses than dyanmic assignment. The practice of static assignment is 'strongly discouraged' by RIPE. IP address requests based on static assignment to dial-up users will be forwarded by IP-Plus to RIPE for a second opinion, as will requests for extra addresses when a large number have already been used in this way. This slows down the assignment procedure considerably.