Cisco 10000-2P2-2DC Software Guide - Page 288

Overlapping IP Address Pools Chapter 10 Configuring Address Pools Command Router# show ip interface [type number] Router# show ip dhcp pool name Purpose Displays the usability status of interfaces configured for IP. 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. 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 10-16 Cisco 10000 Series Router Software Configuration Guide OL-2226-23