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How Waiting List Requests Work

When a block of IPv4 addresses becomes available, ARIN examines the oldest request on the waiting list to determine whether or not the newly available block can fill it. ARIN then continues to the next oldest request as necessary. Waiting list request fulfillment is determined by the size of the available block(s) and the approved maximum and specified minimum acceptable block sizes for each organization. A table showing the current status of the Waiting List is available on the Waiting List for Unmet Requests page.

Below are some example scenarios to help illustrate how the waiting list works in practice.

Scenario 1: Single Block Fills a Single Request

IPv4 Waiting List: Scenario 1
Request's Position on Waiting List Date and Time Added to Waiting List Maximum Approved Prefix Size Minimum Acceptable Prefix Size
1 Mon 03 Aug 2015 12:51:06 -0400 16 17
2 Mon 10 Aug 2015 15:04:56 -0400 20 22

If a /16 becomes available:

Request #1 receives that /16 and is removed from the waiting list.  Your request always receives the maximum approved size as long as it can be filled with the available block.  Request #2 and all other requests on the waiting list move up one spot.

If a /21 becomes available:

Request #1 is bypassed since that organization has indicated their smallest acceptable block size.  Request #1 stays on the waiting list and will only be filled if/when a /17 or /16 becomes available.  Request #2 receives the /21 and is removed from the waiting list.

If a /23 or smaller block becomes available:

Since neither request #1 nor request #2 will accept a block that small, ARIN will continue on to request #3 and move down the list until we find a request that can be filled with that block size.

Scenario 2: Single Block Split to Fill Multiple Requests

IPv4 Waiting List: Scenario 2
Request's Position on Waiting List Date and Time Added to Waiting List Maximum Approved Prefix Size Minimum Acceptable Prefix Size
1 Mon 03 Aug 2015 12:51:06 -0400 17 20
2 Mon 10 Aug 2015 15:04:56 -0400 20 22
3 Fri 14 Aug 2015 10:37:14 -0400 16 17
4 Thu 20 Aug 2015 17:02:29 -0400 18 24

If a /16 becomes available:

  • Request #1 receives a /17 from that /16 and is removed from the waiting list, leaving a /17 available to fill requests on the waiting list.
  • Request #2 receives a /20 from that /17 and is removed from the waiting list, leaving a /20, /19, and /18 available to fill requests on the waiting list.
  • Request #3 receives no space since all available blocks are smaller than /17 and moves up to #1 on the waiting list. Note that older requests are always filled first, so even though request #3 has qualified for a /16, it doesn't get priority over requests #1 and #2.
  • Request #4 receives a /18 and is removed from the waiting list, leaving a /20 and /19. This process continues until all available blocks resulting from the initial split have been issued to organizations on the waiting list.

This process continues until all available blocks resulting from the initial split have been issued to organizations on the waiting list.

Scenario 3a: Multiple Blocks Fill Multiple Requests

When multiple blocks are received back at the same time, the order in which those blocks are used to fill requests is determined by starting with the block that gives the oldest request the largest possible block.  If multiple blocks equal to or larger than the oldest request are available, the smallest is used to fill the oldest request.

IPv4 Waiting List: Scenario 3a
Request's Position on Waiting List Date and Time Added to Waiting List Maximum Approved Prefix Size Minimum Acceptable Prefix Size
1 Mon 03 Aug 2015 12:51:06 -0400 17 20
2 Mon 10 Aug 2015 15:04:56 -0400 17 20
3 Fri 14 Aug 2015 10:37:14 -0400 17 20
4 Thu 20 Aug 2015 17:02:29 -0400 18 24

If ARIN receives a /20 and a /16 at the same time:

  • Request #1 receives a /17 from the available /16 and is removed from the waiting list. Even though both blocks are larger than the oldest request's minimum, the /16 is used since it can fill the oldest request's maximum size and the /20 cannot. This leaves a /17 and /20 available.
  • Request #2 receives a /17 and is removed from the waiting list, leaving a /20 available.
  • Request #3 receives a /20 and is removed from the waiting list.
  • Request #4 receives no space and moves up to #1 on the waiting list.

Scenario 3B: Multiple Blocks Fill Multiple Requests

IPv4 Waiting List: Scenario 3B
Request's Position on Waiting List Date and Time Added to Waiting List Maximum Approved Prefix Size Minimum Acceptable Prefix Size
1 Mon 03 Aug 2015 12:51:06 -0400 21 24
2 Mon 10 Aug 2015 15:04:56 -0400 16 21
3 Fri 14 Aug 2015 10:37:14 -0400 17 21
4 Thu 20 Aug 2015 17:02:29 -0400 18 24

If ARIN receives a /20 and a /16 at the same time:

  • Request #1 is filled with a /21 from the available /20 and is removed from the waiting list.  While both the /20 and /16 could potentially fill this request, the /20 is used because it's smaller and both would result in the maximum /21 being issued.  This leaves a /16 and a /21 available.
  • Request #2 is filled with the /16 and is removed from the waiting list.  When multiple blocks are available (in this case, a /16 and a /21), the request is always filled with a block that fulfills the maximum approved size where possible.  This leaves a /21 available.
  • Request #3 is filled with the /21 and is removed from the waiting list.
  • Request #4 moves up to the top of the waiting list since no space remains available from the two available blocks.

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