IP Address Assignment Pool

Address Assignment Types

Address-assignment pools support both dynamic and static address assignment. In dynamic address assignment, a client is automatically assigned an address from the address-assignment pool. In static address assignment, which is supported for IPv4 pools only, you reserve an address that is then always used by a particular client. Addresses that are reserved for static assignment are removed from the dynamic address pool and cannot be assigned to other clients.

Named Address Ranges in Address Assignment Pool

You can configure named address ranges within an address-assignment pool. A named range is a subset of the overall address range. A client application can use named ranges to manage address assignment based on client-specific criteria. For example, for IPv4 address-assignment pools, you might create a named range that is based on a specific DHCP option 82 value. Then, when a DHCP client request matches the specified option 82 value, an address from the specified range is assigned to the client.

Address Allocation from Linked Address Pools

You can link address-assignment pools together to provide backup pools for address assignment. When no addresses are available in the primary or in the matching address pool, the device automatically proceeds to the linked (secondary) address pool to search for an available address to allocate.

Although the first pool in a chain of linked pools is generally considered the primary pool, a matching pool is not necessarily the first pool in the chain.

Starting in Junos OS Release 18.1R1, search mechanism for an available address proceeds through a chain of linked pools. This behavior enables the DHCP to search addresses contiguously..

Lets use an example on how the search mechanism works. Consider a chain of three pools— A, B, and C. Pool A is the primary pool, Pool B is the matching pool for certain subscribers based on information returned by the RADIUS server. The search for an available address for those subscribers uses the following sequence:

• By default, the matching pool (Pool B) is searched first.

• The search moves to the first pool (Pool A) in the chain if address not found.

• The search proceeds through the chain (Pool C) until an available address is found and allocated, or until the search determines no addresses are free.

• In each pool, all address ranges are fully searched for an address.

You can configure the linked-pool-aggregation statement to start searching within a block of addresses in each range in the matching pool and then successively through the linked pools. The search then moves back to the first pool in the chain and searches all addresses in all ranges in each pool through the last pool in the chain.

Address Pool Hold-Down State

You can configure an address-assignment pool in hold-down state. When the address pool is in hold-down state, the pool is no longer available to allocate IP addresses for the subscribers. This configuration gracefully transforms the active pool to an inactive state as the previously allocated addresses are returned to the pool. When the pool is inactive, you can safely perform maintenance on the pool without affecting any active subscribers.

Address-Assignment Pool for Neighbor Discovery Router Advertisement

You can explicitly allocate an address-assignment pool for Neighbor Discovery Router Advertisement (NDRA).

Excluding Specified Address or Address Range

Starting in Junos OS Release 18.1R1, you can exclude a specified address or range of consecutive addresses to prevent them from being allocated from an address pool.

For example, you might want to reserve certain addresses or ranges to be used only for static subscribers. When you configure an address or range to be excluded, and the address or an address within the range, has already been allocated, that subscriber is logged out, the address is deallocated, and the address is marked for exclusion.

Licensing Requirement

This feature requires a license. To understand more about Subscriber Access Licensing , see Subscriber Access Licensing Overview. Please refer to the Juniper Licensing Guide for general information about License Management. Please refer to the product Data Sheets for details, or contact your Juniper Account Team or Juniper Partner.

Benefits of Address Assignment Pools

• The address-assignment pool feature supports both subscriber management and DHCP management.

• You can create centralized pools of addresses independent of client applications.

• You can specify blocks of addresses, named ranges, so that a given address pool can be used to supply different addresses for different client applications or for subscribers that match different sets of criteria.

• You can link pools together to ensure that pools are searched for free addresses in a specific manner, contiguously or noncontiguously.

• You can gracefully transition an address pool from active to inactive by specifying that no further addresses are allocated from the pool.