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Chapter 10
Configuring Address Pools
Feature History for On-Demand Address Pool Manager
Cisco IOS Release
12.2(15)BX
12.3(7)XI1
12.2(28)SB
Address Allocation for PPP Sessions
For individual address allocation for PPP sessions, the pool manager searches for a free address
beginning with the very first leased subnet. If a free address is not available in the first subnet, the pool
manager searches the second leased subnet, and so on until a free address is found. This method of
address allocation allows for efficient subnet release and route summarization. However, it differs from
the normal DHCP address selection policy in which the IP address of the receiving interface is taken into
account. The on-demand address pool manager feature provides an IP address pooling mechanism for
PPP that allows the DHCP server to distinguish between a normal DHCP address request and an address
request for a PPP client.
Subnet Releasing
The pool manager releases subnets beginning with the last leased subnet. The pool manager searches for
a releasable subnet—a subnet with no addresses currently being leased. If it finds a releasable subnet, it
releases the subnet and removes the summarized route for that subnet. If more than one releasable subnet
exists, the pool manager releases the most recently allocated subnet. The pool manager takes no action
if it does not find a releasable subnet. If the high utilization mark is reached by releasing the subnet, the
pool manager does not release the subnet. Regardless of the instantaneous utilization level, the pool
manager never releases the first leased subnet until it disables the ODAP.
On-Demand Address Pools for MPLS VPNs
The on-demand address pool manager feature provides support for Multiprotocol Label Switching
(MPLS) Virtual Private Network (VPN) environments. This feature automates the resizing of address
pools, reducing network loading and manual configuration.
Each ODAP is configured and associated with a specific MPLS VPN. Each VPN is associated with one
or more VRFs. The VRF maintains a routing table and other information associated with a specific
customer VPN site. The utilization of the on-demand address pool occurs as described in the
"On-Demand Address Pool Manager" section on page
the VRF associated with a particular VPN.
Only the ODAP associated with a specific VPN can allocate addresses to PPP sessions belonging to that
VPN. The PE router on which the ODAP is configured terminates the PPP sessions and maps the remote
user to the corresponding MPLS VPNs.
OL-2226-23
Description
This feature was introduced on the Cisco 10000 series
router.
This feature was integrated into Cisco IOS Release
12.3(7)XI1.
This feature was integrated into Cisco IOS Release
12.2(28)SB.
Cisco 10000 Series Router Software Configuration Guide
On-Demand Address Pool Manager
10-4, except that address allocation occurs within
Required PRE
PRE2
PRE2
PRE2
10-5
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