Ip Address Pool Configuration On The System - Cisco ASR 5000 Series Administration Manual

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▀ IP Address Pool Configuration on the System

IP Address Pool Configuration on the System
Before an MS is able to access data services, they must have an IP address. As described previously, the GGSN supports
static or dynamic addressing (through locally configured address pools on the system, DHCP client-mode, or DHCP
relay-mode). Regardless of the allocation method, a corresponding address pool must be configured.
IP addresses can be dynamically assigned from a single pool/a group of IP pools/a group of IP pool groups. The
addresses/IP pools/ IP pool groups are placed into a queue in each pool or pool group. An address is assigned from the
head of the queue and, when released, returned to the end. This method is known as least recently used (LRU).
On initiation of a session, a request of IP address from IP pool is sent and system assigns an IP address out of
"available" IP address(es) in the pool. This assigned IP address is set to "allocated" state and cannot be used for any
other session during this state. As soon as the session is cleared the state of "allocated" IP address is changed to
"released" and is ready for allocation to any other subscriber session. If a "hold" timer is set for assigned/released IP
address(es), it will go into the "hold" state and remain there till the timer expires. As soon as "hold timer" expires its
state is changed from "hold" to "released" state and it will be available for reallocation. The "available" IPs include
"free" and "released" IP addresses.
Free IPs are used first depending on which subscriber is connecting. Normally same IP is given to a subscriber. So if a
subscriber is connecting again, instead of using a free IP, GGSN allocates the IP which was given to him previously.
This IP will be from the released state. For GGSN, Username and IMSI are used as key for generating subscriber ID
used by VPN while allocating IP from the IP pool. Therefore if the subscriber ID matches to any of the previous ones
for IPs in released state, that IP is re-allocated to that subscriber, otherwise a new IP is allocated.
When a group of pools have the same priority, an algorithm is used to determine a probability for each pool based on the
number of available addresses, then a pool is chosen based on the probability. This method, over time, allocates
addresses evenly from the group of pools.
Important:
frequently.
Important:
system. For more information on commands that configure additional parameters and options, refer ip pool command
section in Context Configuration Mode Commands chapter of Command Line Interface Reference.
These instructions assume that you have already configured the system level configuration as described in System
Administration Guide and GGSN service as described in GGSN Service Configuration section of this chapter.
To configure the IP pool:
Step 1
Create the IP pool for IPv4 addresses in system context by applying the example configuration in the IPv4 Pool
Creation section.
Step 2
Optional. Configure the IP pool for IPv6 addresses in system context by applying the example configuration in the IPv6
Pool Creation section.
Step 3
Verify your IP pool configuration by following the steps in the IP Pool Configuration Verification section.
Step 4
Save your configuration as described in the Verifying and Saving Your Configuration chapter.
▄ Cisco ASR 5000 Series Gateway GPRS Support Node Administration Guide
Setting different priorities on each individual pool can cause addresses in some pools to be used more
This section provides the minimum instruction set for configuring local IP address pools on the
GGSN Service Configuration Procedures
OL-22944-02

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