Table Of Contents
Prerequisites for DHCP ODAP Server Support
Restrictions for DHCP ODAP Server Support
Information About DHCP ODAP Server Support
On-Demand Address Pool Management
How to Configure DHCP ODAP Subnet Allocation Server Support
Configuring a Global Pool on a Subnet Allocation Server
Configuring a VRF Subnet Pool on a Subnet Allocation Server
Using a VPN ID to Configure a VRF Subnet Pool on a Subnet Allocation Server
Verifying the Subnet Allocation and DHCP Bindings
Troubleshooting the DHCP ODAP Subnet Allocation Server
Configuration Examples for DHCP ODAP Server Support
Configuring a Global Pool for a Subnet Allocation Server: Example
Configuring a VRF Pool for a Subnet Allocation Server: Example
Using a VPN ID to Configure a VRF Pool on a Subnet Allocation Server: Example
Verifying Local Configuration on a Subnet Allocation Server: Example
Verifying Address Pool Allocation Information: Example
Verifying Subnet Allocation and DHCP Bindings: Example
DHCP ODAP Server Support
The DHCP ODAP Server Support feature introduces the capability to configure a Cisco IOS Dynamic Host Configuration Protocol (DHCP) server (or router) as a subnet allocation server. This capability allows the IOS DHCP server to be configured with a pool of subnets for lease to On-Demand Address Pool (ODAP) clients. Subnet pools can be configured for global ODAP clients or Multiprotocol Label Switched (MPLS) Virtual Private Network (VPN) ODAP clients on a per-client basis. The DHCP subnet allocation server creates bindings for the subnet leases and stores these leases in the DHCP database. This feature also supports database agents for subnet lease recovery.
Feature Specifications for the DHCP ODAP Server Support Feature
Feature History Release Modification12.2(15)T
This feature was introduced.
12.2(27)SB
This feature was integrated into Cisco IOS Release 12.2(27)SB.
Finding Support Information for Platforms and Cisco IOS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.
Contents
•
Prerequisites for DHCP ODAP Server Support
•
Restrictions for DHCP ODAP Server Support
•
Information About DHCP ODAP Server Support
•
How to Configure DHCP ODAP Subnet Allocation Server Support
•
Configuration Examples for DHCP ODAP Server Support
Prerequisites for DHCP ODAP Server Support
Your network should be configured to run DHCP. You will also need to complete the following tasks before you can configure this feature:
•
Identify an external FTP, TFTP, or remote copy protocol (rcp) server that you will use to store the DHCP bindings database.
•
Configure an ODAP manager in the network.
Restrictions for DHCP ODAP Server Support
A router can be configured as a subnet allocation server and a DHCP server at the same time with one restriction: separate pools must be created for subnet allocation and IP address assignment. An address pool cannot be used by DHCP for both subnet allocation and IP address assignment.
Information About DHCP ODAP Server Support
To configure this feature, you must understand the following concepts
•
On-Demand Address Pool Management
On-Demand Address Pool Management
ODAPs are used to centralize the management of large pools of addresses and simplify the configuration of large networks. ODAP provides a central management point for the allocation and assignment of IP addresses. When a Cisco IOS router is configured as an ODAP manager, pools of IP addresses are dynamically increased or reduced in size depending on the address utilization level. The ODAP manager is supported by centralized RADIUS or DHCP servers and is configured to request an initial pool of addresses from either the RADIUS or DHCP server. The ODAP manager controls IP address assignment and will allocate additional IP addresses as necessary. This method of address allocation and assignment optimizes the use of available address space and simplifies the configuration of medium-sized and large networks.
ODAP Manager Support
The ODAP Server Support feature introduces functionality that allows the ODAP manager to allocate address space on a per-subnet basis. This feature provides the network operator with the capability to configure a Cisco IOS router as a subnet allocation server. The operation of a subnet allocation server is very similar to the operation of a DHCP server, except that pools of subnets are created and assigned instead of pools of IP addresses. Subnet allocation pools are created and configured by using the subnet prefix-length command in DHCP pool configuration mode. The size of each assigned or allocated subnet is set by the prefix-length argument, using standard CIDR bit count notation to determine the number of addresses that are configured in each subnet lease.
When a DHCP server is configured as a subnet allocation server, it provides subnet allocation pools for ODAP manager allocation. The ODAP manager allocates subnets from the subnet allocation server based on the demand for IP addresses and subnet availability. The ODAP manager is configured to allocate an initial amount of address space in the form of subnets. The size of the subnet allocated by the ODAP manager is determined by the subnet size that is configured on the subnet allocation server. The ODAP manager will then assign addresses to clients from these subnets and allocate more subnets as the need for address space increases.
When the ODAP manager allocates a subnet, the subnet allocation server creates a subnet binding. This binding is stored in the DHCP database for as long as the ODAP manager requires the address space. The binding is destroyed and the subnet is returned to the subnet pool only when the ODAP manager releases the subnet as address space utilization decreases.
The subnet allocation server can be configured to assign subnets from subnet pools for global space and from VPN pools for MPLS VPN clients. VPN routes between the ODAP manager and the subnet allocation server are configured based on VRF name or VPN ID configuration. The VRF and VPN ID are configured to maintain routing information that defines customer VPN sites. This customer site is attached to a provider edge (PE) router. A VRF consists of an IP routing table, a derived Cisco Express Forwarding (CEF) table, a set of interfaces that use the forwarding table, and a set of rules and routing protocol parameters that control the information that is included in the routing table.
For more information about ODAP Manager configuration, refer to the DHCP Server—On-Demand Address Pool Manager feature released in 12.2(8)T:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t8/ftondhcp.htm
How to Configure DHCP ODAP Subnet Allocation Server Support
This procedure contains the following tasks:
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Configuring a Global Pool on a Subnet Allocation Server, page 17 (required)
•
Configuring a VRF Subnet Pool on a Subnet Allocation Server, page 19 (optional)
•
Using a VPN ID to Configure a VRF Subnet Pool on a Subnet Allocation Server, page 21 (optional)
•
Verifying the Subnet Allocation and DHCP Bindings, page 23 (optional)
•
Troubleshooting the DHCP ODAP Subnet Allocation Server (optional)
Configuring a Global Pool on a Subnet Allocation Server
Perform this task to configure a global subnet pool on a subnet allocation server.
Global Subnet Pools
Global subnet pools are created in a centralized network. The ODAP manager allocates subnets from the subnet allocation server based on subnet availability. When the ODAP manager allocates a subnet, the subnet allocation server creates a subnet binding. This binding is stored in the DHCP database for as long as the ODAP manager requires the address space. The binding is destroyed and the subnet is returned to the subnet pool only when the ODAP manager releases the subnet as address space utilization decreases.
SUMMARY STEPS
1.
enable
2.
configure terminal
3.
ip dhcp pool pool-name
4.
network network-number [mask | /prefix-length]
5.
subnet prefix-length prefix-length
DETAILED STEPS
Configuring a VRF Subnet Pool on a Subnet Allocation Server
This task shows how to configure a VRF subnet pool on a subnet allocation server.
VRF Subnet Pools
A subnet allocation server can be configured to assign subnets from VRF subnet allocation pools for MPLS VPN clients. VPN routes between the ODAP manager and the subnet allocation server are configured based on VRF name or VPN ID configuration. The VRF and VPN ID are configured to maintain routing information that defines customer VPN sites. The VPN customer site (or Customer Equipment [CE]) is attached to a provider edge (PE) router. The VRF is used to specify the VPN and consists of an IP routing table, a derived Cisco Express Forwarding (CEF) table, a set of interfaces that use the forwarding table, and a set of rules and routing protocol parameters that control the information that is included in the routing table.
Prerequisites
The VRF name and VPN ID can be configured on the ODAP manager and subnet allocation server prior to the configuration of the subnet allocation pool.
SUMMARY STEPS
1.
enable
2.
configure terminal
3.
ip dhcp pool pool-name
4.
vrf vrf-name
5.
network network-number [mask | /prefix-length]
6.
subnet prefix-length prefix-length
DETAILED STEPS
Using a VPN ID to Configure a VRF Subnet Pool on a Subnet Allocation Server
Perform this task to configure a VRF subnet pool, using a VPN ID, on a subnet allocation server.
VRF Pools and VPN IDs
A subnet allocation server can also be configured to assign subnets from VPN subnet allocation pools based on the VPN ID of a client. The VPN ID (or Organizational Unique Identifier [OUI]) is a unique identifier assigned by the IEEE.
Prerequisites
The VRF name and VPN ID can be configured on the ODAP manager and subnet allocation server prior to the configuration of the subnet allocation pool.
SUMMARY STEPS
1.
enable
2.
configure terminal
3.
ip vrf vrf-name
4.
rd route-distinguisher
5.
route-target both route-target-number
6.
vpn id vpn-id
7.
exit
8.
ip dhcp pool pool-name
9.
vrf vrf-name
10.
network network-number [mask | /prefix-length]
11.
subnet prefix-length prefix-length
DETAILED STEPS
Verifying the Subnet Allocation and DHCP Bindings
Perform this task to verify subnet allocation and DHCP bindings.
The show ip dhcp pool and show ip dhcp binding commands do not need to be issued together or even in the same session as there are differences in the information that is provided. These commands, however, can be used to display and verify subnet allocation and DHCP bindings. The show running-config | begin dhcp command is used to display the local configuration of DHCP and the configuration of the subnet prefix-length command.
SUMMARY STEPS
1.
enable
2.
show running-config | begin dhcp
3.
show ip dhcp pool
4.
show ip dhcp binding
DETAILED STEPS
Troubleshooting the DHCP ODAP Subnet Allocation Server
Perform this task to troubleshoot the DHCP ODAP subnet allocation server.
SUMMARY STEPS
1.
enable
2.
debug dhcp [detail]
3.
debug ip dhcp server
DETAILED STEPS
Configuration Examples for DHCP ODAP Server Support
This section provides the following configuration examples:
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Configuring a Global Pool for a Subnet Allocation Server: Example
•
Configuring a VRF Pool for a Subnet Allocation Server: Example
•
Using a VPN ID to Configure a VRF Pool on a Subnet Allocation Server: Example
•
Verifying Local Configuration on a Subnet Allocation Server: Example
•
Verifying Address Pool Allocation Information: Example
•
Verifying Subnet Allocation and DHCP Bindings: Example
Configuring a Global Pool for a Subnet Allocation Server: Example
The following example shows how to configure a router to be a subnet allocation server and create a global subnet allocation pool named "GLOBAL-POOL" that allocates subnets from the 10.0.0.0/24 network. The configuration of the subnet prefix-length command in this example configures the size of each subnet that is allocated from the subnet pool to support 254 host IP addresses.
ip dhcp pool GLOBAL-POOLnetwork 10.0.0.0 255.255.255.0subnet prefix-length 24!Configuring a VRF Pool for a Subnet Allocation Server: Example
The following example shows how to configure a router to be a subnet allocation server and create a VRF subnet allocation pool named "VRF-POOL" that allocates subnets from the 172.16.0.0/16 network and configures the VPN to match the VRF named "RED." The configuration of the subnet prefix-length command in this example configures the size of each subnet that is allocated from the subnet pool to support 62 host IP addresses.
ip dhcp pool VRF-POOLvrf REDnetwork 172.16.0.0 /16subnet prefix-length 26!Using a VPN ID to Configure a VRF Pool on a Subnet Allocation Server: Example
The following example shows how to configure a router to be a subnet allocation server and create a VRF subnet allocation pool named "VRF-POOL" that allocates subnets from the 192.168.0.0/24 network and configures the VRF named "RED." The VPN ID must match the unique identifier that is assigned to the client site. The route target and route distinguisher are configured in the as-number:network-number format. The route target and route distinguisher must match. The configuration of the subnet prefix-length command in this example configures the size of each subnet that is allocated from the subnet pool to support 30 host IP addresses.
ip vrf REDrd 100:1route-target both 100:1vpn id 1234:123456exitip dhcp pool VPN-POOLvrf REDnetwork 192.168.0.0 /24subnet prefix-length /27exitVerifying Local Configuration on a Subnet Allocation Server: Example
The following example is output from the show running-config command. This command can be used to verify the local configuration on a subnet allocation server. The output from this command displays the configuration of the subnet prefix-length command under the DHCP pool named "GLOBAL-POOL." The total size of the subnet allocation pool is set to 254 addresses with the network command. The configuration of the subnet prefix-length command configures this pool to allocate a subnet that will support 254 host IP addresses. Because the total pool size supports only 254 addresses, only one subnet can be allocated from this pool.
Router# show running-config | begin dhcpip dhcp pool GLOBAL-POOLnetwork 10.0.0.0 255.255.255.0subnet prefix-length 24!Verifying Address Pool Allocation Information: Example
The following examples are output from the show ip dhcp pool command. This command can be used to verify subnet allocation pool configuration on the subnet allocation server and the ODAP manager. The output from this command displays information about the address pool name, utilization level, configured subnet size, total number of addresses (from subnet), pending events, and specific subnet lease information.
The following sample output shows that the configured subnet allocation size is /24 (254 IP addresses), that there is a pending subnet allocation request, and there are no subnets in the pool:
Router> show ip dhcp pool ISP-1Pool ISP-1 :Utilization mark (high/low) :100 / 0Subnet size (first/next) :24 / 24 (autogrow)Total addresses :0Leased addresses :0Pending event :subnet request0 subnet is currently in the poolThe next example shows that the configured subnet allocation size is /24 (254 IP address), the configured VRF name is "RED", and a subnet containing 254 IP addresses has been allocated but no IP addresses have been leased from the subnet:
Router> show ip dhcp pool SUBNET-ALLOCPool SUBNET-ALLOC :Utilization mark (high/low) :100 / 0Subnet size (first/next) :24 / 24 (autogrow)VRF name :REDTotal addresses :254Leased addresses :0Pending event :none1 subnet is currently in the pool :Current index IP address range Leased addresses10.0.0.1 10.0.0.1 - 10.0.0.254 0Verifying Subnet Allocation and DHCP Bindings: Example
The following example is from the show ip dhcp binding command. This command can be used to display subnet allocation to DHCP binding mapping information. The output of this command shows the subnet lease to MAC address mapping, the lease expiration, and the lease type (subnet lease bindings are configured to be automatically created and released by default). The output that is generated for DHCP IP address assignment and subnet allocation is almost identical, except that subnet leases display an IP address followed by the subnet mask (which shows the size of the allocated subnet) in CIDR bit count notation. Bindings for individual IP address only display an IP address and are not followed by a subnet mask.
Router# show ip dhcp bindingBindings from all pools not associated with VRF:IP address Client-ID/ Lease expiration TypeHardware address/User name10.0.0.0/26 0063.6973.636f.2d64. Mar 29 2003 04:36 AM Automatic656d.6574.6572.2d47.4c4f.4241.4cAdditional References
For additional information related to the DHCP ODAP Server Support feature, refer to the following references:
Related Documents
Related Topic Document TitleDHCP commands
Cisco IOS IP Command Reference, Volume 1 of 3: Addressing and Services, Release 12.2
DHCP configuration tasks
Cisco IOS IP Configuration Guide, Release 12.2
ODAP manager configuration tasks
DHCP Server—On-Demand Address Pool Manager, Release 12.2(15)T
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t15/ftondhcp.htm
Standards
Standards TitleNo new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
—
MIBs
RFCs
RFCs 1 TitleRFC 2131
Dynamic Host Configuration Protocol
RFC 2132
DHCP Options and BOOTP Vendor Extensions
draft-ietf-dhc-agent-vpn-id-02.txt
VPN Identifier sub-option for the Relay Agent Information Option
draft-ietf-dhc-subnet-alloc-00.txt
Subnet Allocation using DHCP
draft-ietf-dhc-vpn-option-02.txt
DHCP VPN Information option
1 Not all supported RFCs are listed.
Technical Assistance
Command Reference
This section documents new and modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.2 command reference publications.
subnet prefix-length
To configure a subnet allocation pool and determine the size subnets that are allocated from the pool, use the subnet prefix-length command in DHCP pool configuration mode. To unconfigure subnet pool allocation, use the no form of this command.
subnet prefix-length prefix-length
no subnet prefix-length prefix-length
Syntax Description
prefix-length
Configures the IP subnet prefix length in classless interdomain routing (CIDR) bit count notation. The range is from 1 to 31.
Defaults
No default behavior or values.
Command Modes
DHCP pool configuration
Command History
Release Modification12.2(15)T
This command was introduced.
12.2(27)SBA
This command was integrated.
Usage Guidelines
This command is used to configure a Cisco IOS router as a subnet allocation server for a centralized or remote VPN on-demand address pool (ODAP) manager. This command is configured under a DHCP pool. The prefix-length argument is used to determine the size of the subnets that are allocated from the subnet allocation pool. The values that can be configured for the prefix-length argument follow CIDR bit count notation format.
Configuring Global Subnet Pools
Global subnet pools are created in a centralized network. The ODAP server allocates subnets from the subnet allocation server based on subnet availability. When the ODAP manager allocates a subnet, the subnet allocation server creates a subnet binding. This binding is stored in the DHCP database for as long as the ODAP server requires the address space. The binding is destroyed and the subnet is returned to the subnet pool only when the ODAP server releases the subnet as address space utilization decreases.
Configuring VPN Subnet Pools
A subnet allocation server can be configured to assign subnets from VPN subnet allocation pools for MPLS VPN clients. VPN routes between the ODAP manager and the subnet allocation server are configured based on VRF name or VPN ID configuration. The VRF and VPN ID are configured to maintain routing information that defines customer VPN sites. This customer site is attached to a provider edge (PE) router. A VRF consists of an IP routing table, a derived Cisco Express Forwarding (CEF) table, a set of interfaces that use the forwarding table, and a set of rules and routing protocol parameters that control the information that is included in the routing table.
Configuring VPN Subnet Pools for VPN clients with VPN IDs
A subnet allocation server can also be configured to assign subnets from VPN subnet allocation pools based on the VPN ID of a client. The VPN ID (or Organizational Unique Identifier [OUI]) is a unique identifier assigned by the IEEE. VPN routes between the ODAP manager and the subnet allocation server are enabled by configuring the DHCP pool with a VPN ID that matches the VPN ID that is configured for the VPN client.
Examples
Global Configuration Example
The following example configures a router to be a subnet allocation server and creates a global subnet allocation pool named GLOBAL-POOL from the 10.0.0.0 network. The configuration of the subnet prefix-length command in this example configures each subnet that is allocated from the subnet pool to support 254 host IP addresses.
Router(config)# ip dhcp pool GLOBAL-POOLRouter(dhcp-config)# network 10.0.0.0 255.255.255.0Router(dhcp-config)# subnet prefix-length 24!VPN Configuration Example
The following example configures a router to be a subnet allocation server and creates a VRF subnet allocation pool named VRF-POOL from the 172.16.0.0 network and configures the VPN to match the VRF named RED. The configuration of the subnet prefix-length command in this example configures each subnet that is allocated from the subnet pool to support 62 host IP addresses.
Router(config)# ip dhcp pool VRF-POOLRouter(dhcp-config)# vrf REDRouter(dhcp-config)# network 172.16.0.0 /16Router(dhcp-config)# subnet prefix-length 26!VPN ID Configuration Example
The following example configures a router to be a subnet allocation server and creates a VRF subnet allocation pool named VRF-POOL from the 192.168.0.0 network and configures the VRF named RED. The VPN ID must match the unique identifier that is assigned to the client site. The route target and route distinguisher are configured in the as-number:network number format. The route target and route distinguisher must match. The configuration of the subnet prefix-length command in this example configures each subnet that is allocated from the subnet pool to support 30 host IP addresses.
Router(config)# ip vrf REDRouter(config-vrf)# rd 100:1Router(config-vrf)# route-target both 100:1Router(config-vrf)# vpn id 1234:123456Router(config-vrf)# exitRouter(config)# ip dhcp pool VPN-POOLRouter(dhcp-config)# vrf REDRouter(dhcp-config)# network 192.168.0.0 /24Router(dhcp-config)# subnet prefix-length /27Router(dhcp-config)# exitRelated Commands
show ip dhcp binding
To display address bindings on the Cisco IOS Dynamic Host Configuration Protocol (DHCP) server, use the show ip dhcp binding command in user or privileged EXEC mode.
show ip dhcp binding [ip-address]
Syntax Description
ip-address
(Optional) Specifies the IP address of the DHCP client for which bindings will be displayed.
Command Modes
User EXEC
Privileged EXECCommand History
Release Modification12.0(1)T
This command was introduced.
12.2(15)T
Support to display allocated subnets was added to the output.
12.2(27)SBA
This command was integrated.
Usage Guidelines
This command is used to display DHCP binding information for IP address assignment and subnet allocation. If the address is not specified, all address bindings are shown. Otherwise, only the binding for the specified client is displayed. The output from this command displays binding information for individual IP address assignment and allocated subnets. The output that is generated for DHCP IP address assignment and subnet allocation is almost identical, except that subnet leases display an IP address followed by the subnet mask (which shows the size of the allocated subnet). Bindings for individual IP address only display an IP address and are not followed by a subnet mask.
Examples
IP Address Assignment Example
The following examples show the DHCP binding address parameters, including an IP address, an associated MAC address, a lease expiration date, and the type of address assignment that have occurred. Table 1 lists descriptions of the fields in each example.
Router#show ip dhcp binding 172.16.1.11IP address Hardware address Lease expiration Type172.16.1.11 00a0.9802.32de Feb 01 1998 12:00 AM AutomaticRouter#show ip dhcp binding 172.16.3.254IP address Hardware address Lease expiration Type172.16.3.254 02c7.f800.0422 Infinite Manual
Subnet Allocation Example
The following example shows the subnet lease to MAC address mapping, the lease expiration, and the lease type (subnet lease bindings are configured to be automatically created and released by default). The output that is generated for DHCP IP address assignment and subnet allocation is almost identical, except that subnet leases display an IP address followed by the subnet mask (which shows the size of the allocated subnet) in CIDR bit count notation. Bindings for an individual IP address only display an IP address and are not followed by a subnet mask. Table 2 lists descriptions of the fields in each example.
Router# show ip dhcp bindingBindings from all pools not associated with VRF:IP address Client-ID/ Lease expiration TypeHardware address/User name10.0.0.0/26 0063.6973.636f.2d64. Mar 29 2003 04:36 AM Automatic656d.6574.6572.2d47.4c4f.4241.4c
Related Commands
Command Descriptionclear ip dhcp binding
Deletes an automatic address binding from the Cisco IOS DHCP server database.
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