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Cisco 10000 Series Router Software Configuration Guide
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Chapter 10 Configuring Address Pools
Overlapping IP Address Pools
Tip
•
By default, the Cisco IOS DHCP server that the pool manager uses verifies address availability by
using the
ping
command before allocating the address; the default DHCP ping configuration waits
two seconds for an ICMP echo reply. As a result of this default configuration, the DHCP server
services one address request every two seconds. You can configure the number of ping packets sent
and the ping timeout timer. To reduce the address allocation time, reduce either the timeout timer
value or the number of ping packets sent.
Note
While reducing the address allocation time improves address allocation, the reduced time
inhibits the DHCP server’s ability to detect duplicate addresses.
•
Each ODAP retries up to four times to obtain a subnet from the DHCP server or the RADIUS server.
If unsuccessful, the subnet request automatically starts when another individual address request is
made to the pool (for example, a newly brought up PPP session makes an address request). If the
address allocation server has not allocated any subnets to a pool, you can force the subnet request
process to restart by using the
clear ip dhcp pool name subnet *
command in privileged EXEC
mode.
Overlapping IP Address Pools
The Overlapping IP Address Pools feature enables you to use multiple IP address spaces and reuse IP
addresses among different VPNs supported on the Cisco 10000 router. Duplicate IP addresses cannot
reside in the same IP address space.
To uniquely place IP addresses within a given IP address space, multiple address spaces are assigned to
IP address groups. This also allows for the verification of nonoverlapping IP address pools within an IP
address group. Within the Cisco 10000 router, use unique pool names. Each pool name has an implicit
group identifier to ensure that it is associated with only one group.
The Cisco 10000 router considers pools without an explicit group name as members of a base system
group and processes these pools as if the IP addresses belong to a single IP address space. You cannot
assign a given IP address multiple times from the pool of a single IP address space.
Existing configurations are not affected by the Overlapping IP Address Pools feature. The processing of
pools that are not specified as a member of a group is unchanged from the existing implementation.
The Overlapping IP Address Pools feature is useful in the following deployment models:
•
Managed L2TP Network Server
•
PPP Terminated Aggregation (PTA) to VRF
•
Remote Access (RA) to MPLS VPN
Router#
show ip interface
[
type number
]
Displays the usability status of interfaces configured for IP.
Router#
show ip dhcp pool
name
Displays DHCP address pool information. Use this command to
check that the DHCP pool assigns an IP address for each
incoming PPP session and associates the address with the correct
VRF.
Command
Purpose
