Table Of Contents

Configuring the DHCP Server On-Demand Address Pool Manager

Contents

Prerequisites for Configuring the DHCP Server On-Demand Address Pool Manager

Restrictions for Configuring the DHCP Server On-Demand Address Pool Manager

Information About the DHCP Server On-Demand Address Pool Manager

ODAP Manager Operation

Subnet Allocation Server Operation

Benefits of Using ODAPs

How to Configure the DHCP Server On-Demand Address Pool Manager

Defining DHCP ODAPs as the Global Default Mechanism

Defining DHCP ODAPs on an Interface

Configuring the DHCP Pool as an ODAP

Configuring ODAPs to Obtain Subnets Through IPCP Negotiation

Configuring AAA

Configuring RADIUS

Disabling ODAPs

Verifying ODAP Operation

Troubleshooting Tips

Monitoring and Maintaining the ODAP

How to Configure DHCP ODAP Subnet Allocation Server Support

Configuring a Global Pool on a Subnet Allocation Server

Global Subnet Pools

Configuring a VRF Subnet Pool on a Subnet Allocation Server

VRF Subnet Pools

Prerequisites

Using a VPN ID to Configure a VRF Subnet Pool on a Subnet Allocation Server

VRF Pools and VPN IDs

Prerequisites

Verifying the Subnet Allocation and DHCP Bindings

Troubleshooting the DHCP ODAP Subnet Allocation Server

Configuration Examples for DHCP Server On-Demand Address Pool Manager

Defining DHCP ODAPs as the Global Default Mechanism: Example

Defining DHCP ODAPs on an Interface: Example

Configuring the DHCP Pool as an ODAP: Example

Configuring the DHCP Pool as an ODAP for Non-MPLS VPNs: Example

IPCP Subnet Mask Delivery: Example

Configuring AAA and RADIUS: Example

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

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Glossary

Feature Information for the DHCP Server On-Demand Address Pool Manager

Configuring the DHCP Server On-Demand Address Pool Manager

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The Cisco IOS DHCP server on-demand address pool (ODAP) manager is 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. A DHCP pool configured in the router can also be used as an IP address pooling mechanism. The IP address pooling mechanism is configured in the router to specify the source of IP addresses for PPP peers.

Module History

This module was first published on May 2, 2005, and last updated on February 27, 2006.

Finding Feature Information in This Module

Your Cisco IOS software release may not support all features. To find information about feature support and configuration, use the "Feature Information for the DHCP Server On-Demand Address Pool Manager" section.

Contents

•Prerequisites for Configuring the DHCP Server On-Demand Address Pool Manager

•Restrictions for Configuring the DHCP Server On-Demand Address Pool Manager

•Information About the DHCP Server On-Demand Address Pool Manager

•How to Configure the DHCP Server On-Demand Address Pool Manager

•How to Configure DHCP ODAP Subnet Allocation Server Support

•Configuration Examples for DHCP Server On-Demand Address Pool Manager

•Additional References

•Glossary

•Feature Information for the DHCP Server On-Demand Address Pool Manager

Prerequisites for Configuring the DHCP Server On-Demand Address Pool Manager

Before you configure the ODAP manager, you should understand the concepts documented in the "DHCP Overview" module.

You must configure standard Multiprotocol Label Switching (MPLS) Virtual Private Networks (VPNs) unless you intend to use non-MPLS VPNs.

In order for the IP address pooling mechanism to work correctly, the VPN routing and forwarding instance (VRF) of the PPP session must match that configured on the pool. Typically this matching is done either by configuring the ip vrf forwarding vrf-name command on the virtual template interface, or if AAA is used to authorize the PPP user, it can be part of the user's profile configuration.

Restrictions for Configuring the DHCP Server On-Demand Address Pool Manager

•The ip dhcp excluded-address global configuration command cannot be used to exclude addresses from VRF associated pools.

•The vrf DHCP pool configuration command is currently not supported for host pools.

•Attribute inheritance is not supported on VRF pools.

•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 the DHCP Server On-Demand Address Pool Manager

Before you configure an ODAP, you should understand the following concepts:

•ODAP Manager Operation

•Subnet Allocation Server Operation

•Benefits of Using ODAPs

ODAP Manager Operation

ODAPs enable pools of IP addresses to be dynamically increased or reduced in size depending on the address utilization level. Once configured, the ODAP is populated with one or more subnets leased from a source server and is ready to serve address requests from DHCP clients or from PPP sessions. The source server can be a remote DHCP server or a RADIUS server (via AAA). Currently, only the Cisco Access Registrar RADIUS server supports ODAPs. Subnets can be added to the pool when a certain utilization level (high utilization mark) is achieved. When the utilization level falls below a certain level (low utilization mark), a subnet can be returned to the server from which it was originally leased. Summarized routes for each leased subnet must be inserted or removed from the related VRF with each addition or removal of subnets into the ODAP.

ODAPs support address assignment using DHCP for customers using private addresses such as in MPLS VPNs. VPNs allow the possibility that two pools in separate networks can have the same address space, with private network addresses, served by the same DHCP server. These IP addresses can be distinguished by a VPN identifier to help select the VPN to which the client belongs.

Each ODAP is configured and associated with a particular MPLS VPN. Cisco IOS software also supports non-MPLS VPN address pools by adding pool name support to the peer default ip address dhcp-pool pool-name command.

For MPLS VPNs, each VPN is associated with one or more VRFs. The VRF is a key element in the VPN technology because it maintains the routing information that defines a customer VPN site. 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.

A PPP session belonging to a specific VPN is only allocated an address from the ODAP associated with that VPN. These PPP sessions are terminated on a Virtual Home Gateway (VHG)/PE router where the ODAP is configured. The VHG/PE router maps the remote user to the corresponding MPLS VPNs.

For PPP sessions, individual address allocation from an ODAP follows a First Leased subnet First (FLF) policy. FLF searches for a free address beginning on the first leased subnet, followed by a search on the second leased subnet if no free address is available in the first subnet, and so on. This policy provides the benefit of grouping the leased addresses over time to a set of subnets, which allows an efficient subnet release and route summarization.

However, the FLF policy differs from the normal DHCP address selection policy. Normal DHCP address selection takes into account the IP address of the receiving interface or the gateway address if it is nonzero. To support both policies, the DHCP server needs to be able to distinguish between a normal DHCP address request and an address request for a PPP client. The ODAP manager uses an IP address pooling mechanism for PPP that allows the DHCP server to distinguish between a normal DHCP address request and a request from a PPP client.

Subnet release from an ODAP follows a Last Leased subnet First (LLF) policy, which prefers the last leased subnet to be released first. This LLF policy searches for a releasable subnet (a subnet with no addresses currently being leased) starting with the last leased subnet. If a releasable subnet is found (candidate subnet), it is released, and the summarized route for that subnet is removed. If more than one releasable subnet exists at that time, only the most recently allocated is released. If there are no releasable subnets, no action is taken. If by releasing the candidate subnet, the high utilization mark is reached, the subnet is not released. The first leased subnet is never released (regardless of the instantaneous utilization level) until the ODAP is disabled.

When a DHCP pool receives multiple subnets from an upstream DHCP server, an address from each subnet is automatically configured on the client connected interface so that the addresses within the subnets can be requested by DHCP clients.

The first address in the first subnet is automatically assigned to the primary address on the interface. The first address of each subsequent subnet is assigned to secondary addresses on the interface. In addition, as client addresses are reclaimed, the count of lease addresses for that subnet is decremented. Once a lease counter for a subnet reaches zero (that is, lease expiry), the subnet is returned to the pool. The previous address on the interface is removed and the first secondary address on the interface is promoted as the primary address of the interface.

Figure 1 shows an ODAP manager configured on the Cisco IOS DHCP server. The ODAP requests an initial pool from the AAA server. Clients make DHCP requests and the DHCP server fulfills requests from the pool. When the utilization rate meets 90 percent, the ODAP manager requests an expansion and the AAA server allocates another subnet from which the ODAP manager can allocate addresses.

Figure 1 ODAP Address Pool Management for MPLS VPNs

Subnet Allocation Server Operation

You can also configure the ODAP manager to allocate subnets instead of individual IP addresses.

This capability allows the network operator to configure a Cisco IOS router as a subnet allocation server. The operation of a subnet allocation server is 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 Common InterDomain Routing (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. In Figure 2, Router B is the subnet allocation server and allocates subnets to the ODAP manager based on the demand for IP addresses and subnet availability. Router B is configured to allocate an initial amount of address space in the form of subnets to the ODAP manager. 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.

Figure 2 Subnet Allocation Server Topology

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 removed 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 also be associated with a VRF. A VRF consists of an IP routing table, a derived 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.

Benefits of Using ODAPs

Efficient Address Management

The ODAP manager allows customers to optimize their use of IP addresses, thus conserving address space.

Efficient Route Summarization and Update

The ODAP manager inserts a summarized route when a subnet is added to the ODAP.

Multiple VRF and Independent Private Addressing Support

The ODAP manager automatically injects subnet routing information into the appropriate VRF.

How to Configure the DHCP Server On-Demand Address Pool Manager

This procedure contains the following tasks:

•Defining DHCP ODAPs as the Global Default Mechanism (required)

•Defining DHCP ODAPs on an Interface (optional)

•Configuring the DHCP Pool as an ODAP (required)

•Configuring ODAPs to Obtain Subnets Through IPCP Negotiation (optional)

•Configuring AAA (required)

•Configuring RADIUS (required)

•Disabling ODAPs (optional)

•Verifying ODAP Operation (optional)

•Monitoring and Maintaining the ODAP (optional)

Defining DHCP ODAPs as the Global Default Mechanism

Perform this task to specify that the global default mechanism to use is on-demand address pooling.

IP addressing allows configuration of a global default address pooling mechanism. The DHCP server needs to be able to distinguish between a normal DHCP address request and an address request for a PPP client.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip address-pool dhcp-pool

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip address-pool dhcp-pool Example: Router(config)# ip address-pool dhcp-pool	Enables on-demand address pooling as the global default IP address mechanism. •For remote access (PPP) sessions into MPLS VPNs, IP addresses are obtained from locally configured VRF-associated DHCP pools.

Defining DHCP ODAPs on an Interface

Perform this task to configure on-demand address pools on an interface.

The interface on-demand address pooling configuration overrides the global default mechanism on that interface.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. peer default ip address dhcp-pool [pool-name]

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	interface type number Example: Router(config)# interface Virtual-Template1	Specifies the interface and enters interface configuration mode.
Step 4	peer default ip address dhcp-pool [pool-name] Example: Router(config)# peer default ip address dhcp-pool mypool	Specifies an IP address from an on-demand address pool to be returned to a remote peer connecting to this interface. •The pool-name argument supports non-MPLS VPNs and is mandatory if the session is not associated with any VRF. Multiple pool names can be accepted but must be separated by white space.

Configuring the DHCP Pool as an ODAP

Perform this task to configure a DHCP address pool as an ODAP pool.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip dhcp pool pool-name

4. vrf name

5. origin {dhcp | aaa | ipcp} [subnet size initial size [autogrow size]]

6. utilization mark low percentage-number

7. utilization mark high percentage-number

8. end

9. show ip dhcp pool [pool-name]

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip dhcp pool pool-name Example: Router(config)# ip dhcp pool red-pool	Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode.
Step 4	vrf name Example: Router(dhcp-config)# vrf red	(Optional) Associates the address pool with a VRF name. •Only use this command for MPLS VPNs.
Step 5	origin {dhcp | aaa | ipcp} [subnet size initial size [autogrow size]] Example: Router(dhcp-config)# origin dhcp subnet size initial /16 autogrow /16	Configures an address pool as an on-demand address pool. •If you do not configure the pool as an autogrow pool, the pool will not request additional subnets if one subnet is already in the pool. •You can enter size as either the subnet mask (nnnn.nnnn.nnnn.nnnn) or prefix size (/nn). The valid values are /0 and /4 to /30. •When a DHCP pool receives multiple subnets from an upstream DHCP server, an address from each subnet is automatically configured on the client connected interface so that the addresses within the subnets can be requested by DHCP clients. The first address in the first subnet is automatically assigned to the primary address on the interface. The first address of each subsequent subnet is assigned to secondary addresses on the interface. In addition, as client addresses are reclaimed, the count of lease addresses for that subnet is decremented. Once a lease counter for a subnet reaches zero (that is, lease expiry), the subnet is returned to the pool. The previous address on the interface is removed and the first secondary address on the interface is promoted as the primary address of the interface. •If the origin aaa option is configured, AAA must be configured.
Step 6	utilization mark low percentage-number Example: Router(dhcp-config)# utilization mark low 40	Sets the low utilization mark of the pool size. •This command cannot be used unless the autogrow size option of the origin command is configured. •The default value is 0 percent.
Step 7	utilization mark high percentage-number Example: Router(dhcp-config)# utilization mark high 60	Sets the high utilization mark of the pool size. •This command cannot be used unless the autogrow size option of the origin command is configured. •The default value is 100 percent.
Step 8	end Example: Router(dhcp-config)# end	Returns to global configuration mode.
Step 9	show ip dhcp pool [pool-name] Example: Router# show ip dhcp pool	(Optional) Displays information about DHCP address pools. •Information about the primary and secondary interface address assignment is also displayed.

Configuring ODAPs to Obtain Subnets Through IPCP Negotiation

Perform this task to configure your router to use subnets obtained through IP Control Protocol (IPCP) negotiation.

You can assign IP address pools to customer premises equipment (CPE) devices, which, in turn, assign IP addresses to the CPE and to a DHCP pool. This functionality has three requirements:

•The Cisco IOS CPE device must be able to request and use the subnet.

•The RADIUS server (via AAA) must be able to provide that subnet and insert the framed route into the proper VRF table.

•The PE router must be able to facilitate providing the subnet through (IPCP) negotiation.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip dhcp pool pool-name

4. import all

5. origin ipcp

6. exit

7. interface type number

8. ip address pool pool-name

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip dhcp pool pool-name Example: Router(config)# ip dhcp pool red-pool	Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode.
Step 4	import all Example: Router(dhcp-config)# import all	Imports option parameters into the Cisco IOS DHCP server database.
Step 5	origin ipcp Example: Router(dhcp-config)# origin ipcp	Configures an address pool as an on-demand address pool using IPCP as the subnet allocation protocol.
Step 6	exit Example: Router(dhcp-config)# exit	Exits DHCP pool configuration mode.
Step 7	interface type number Example: Router(config)# interface ethernet 0	Specifies the interface and enters interface configuration mode.
Step 8	ip address pool pool-name Example: Router(config-if)# ip address pool red-pool	Specifies that the interface IP address will be automatically configured from the named pool, when the pool is populated with a subnet from IPCP.

Configuring AAA

Perform this task to configure AAA.

To allow ODAP to obtain subnets from the RADIUS server, the AAA client must be configured on the VHG/PE router.

SUMMARY STEPS

1. enable

2. configure terminal

3. aaa new-model

4. aaa authorization configuration default group radius

5. aaa accounting network default start-stop group radius
or
aaa accounting network default stop-only group radius

6. aaa session-id common

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	aaa new-model Example: Router(config)# aaa new-model	Enables AAA access control.
Step 4	aaa authorization configuration default group radius Example: Router(config)# aaa authorization configuration default group radius	Downloads static route configuration information from the AAA server using RADIUS.
Step 5	aaa accounting network default start-stop group radius or aaa accounting network default stop-only group radius Example: Router(config)# aaa accounting network default start-stop group radius or Example: Router(config)# aaa accounting network default stop-only group radius	Enables AAA accounting of requested services for billing or security purposes when you use RADIUS. Sends a "start" accounting notice at the beginning of a process. or Enables AAA accounting of requested services for billing or security purposes when you use RADIUS. Sends a "stop" accounting notice at the end of the requested user process.
Step 6	aaa session-id common Example: Router(config)# aaa session-id common	Ensures that the same session ID will be used for each AAA accounting service type within a call.

Configuring RADIUS

Perform this task to configure RADIUS.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip radius source-interface subinterface-name

4. radius-server host ip-address auth-port port-number acct-port port-number

5. radius server attribute 32 include-in-access-req

6. radius server attribute 44 include-in-access-req

7. radius-server vsa send accounting

8. radius-server vsa send authentication

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip radius source-interface subinterface-name Example: Router(config)# ip radius source-interface Ethernet1/1	Forces RADIUS to use the IP address of a specified interface for all outgoing RADIUS packets.
Step 4	radius-server host ip-address auth-port port-number acct-port port-number Example: Router(config)# radius-server host 172.16.1.1 auth-port 1645 acct-port 1646	Specifies a RADIUS server host. •The ip-address argument specifies the IP address of the RADIUS server host.
Step 5	radius server attribute 32 include-in-access-req Example: Router(config)# radius server attribute 32 include-in-access-req	Sends RADIUS attribute 32 (NAS-Identifier) in an access request or accounting request.
Step 6	radius server attribute 44 include-in-access-req Example: Router(config)# radius server attribute 44 include-in-access-req	Sends RADIUS attribute 44 (Accounting Session ID) in an access request or accounting request.
Step 7	radius-server vsa send accounting Example: Router(config)# radius-server vsa send accounting	Configures the network access server (NAS) to recognize and use vendor-specific accounting attributes.
Step 8	Router(config)# radius-server vsa send authentication Example: Router(config)# radius-server vsa send authentication	Configures the NAS to recognize and use vendor-specific authentication attributes.

Disabling ODAPs

This task shows how to disable an ODAP from a DHCP pool.

When an ODAP is disabled, all leased subnets are released. If active PPP sessions are using addresses from the released subnets, those sessions will be reset. DHCP clients leasing addresses from the released subnets will not be able to renew their leases.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip dhcp pool pool-name

4. no origin {dhcp | aaa | ipcp}

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip dhcp pool pool-name Example: Router(config)# ip dhcp pool red-pool	Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode.
Step 4	no origin {dhcp | aaa | ipcp} Example: Router(dhcp-config)# no origin dhcp	Disables the ODAP.

Verifying ODAP Operation

Perform this task to verify ODAP operation.

SUMMARY STEPS

1. enable

2. show ip dhcp pool [pool-name]

3. show ip dhcp binding

DETAILED STEPS

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Step 1 enable

Enables privileged EXEC mode. Enter your password if prompted.

Router> enable

Step 2 show ip dhcp pool [pool-name]

The following output is for two DHCP pools: Green and Global. Pool Green is configured with a high utilization mark of 50 and a low utilization mark of 30. The pool is also configured to obtain more subnets when the high utilization mark is reached (autogrow). The Subnet size field indicates the values configured in the origin command as the initial and incremental subnet sizes that would be requested by the pool named Green. The Total addresses field is a count of all the usable addresses in the pool. The Leased addresses field is a total count of how many bindings were created from the pool. The Pending event field shows subnet request, which means that a subnet request is pending for the pool. The subnet request was scheduled because the Leased addresses count has exceeded the high utilization level of the pool. Subnets currently added to pool Green are shown in sequence. The Current index column shows the address that would be allocated next from this subnet. The IP address range column shows the range of usable addresses from the subnet. The Leased addresses column shows individual count of bindings created from each subnet. Three subnets are currently added to pool Green. The first two subnets have used all their addresses and thus the Current index is showing 0.0.0.0.

Notice that pool Green and pool Global can have the same subnet (172.16.0.1-172.16.0.6) because pool Green is configured to be in VRF Green, while pool Global is configured to be in the global address space.

Router# show ip dhcp pool 

 
Pool Green :

 Utilization mark (high/low)    : 50 / 30

 Subnet size (first/next)       : 24 / 24 (autogrow)

 VRF name                       : Green

 Total addresses                : 18

 Leased addresses               : 13

 Pending event                  : subnet request

 3 subnets are currently in the pool :

 Current index        IP address range                    Leased addresses

 0.0.0.0              172.16.0.1       - 172.16.0.6        6

 0.0.0.0              172.16.0.9       - 172.16.0.14       6

 172.16.0.18          172.16.0.17      - 172.16.0.22       1

Pool Global :

 Utilization mark (high/low)    : 100 / 0 

 Subnet size (first/next)       : 24 / 24 (autogrow)

 Total addresses                : 6

 Leased addresses               : 0

 Pending event                  : none

 1 subnet is currently in the pool :

 Current index        IP address range                    Leased addresses

 172.16.0.1           172.16.0.1       - 172.16.0.6        0

Step 3 show ip dhcp binding

The following output shows the bindings from pool Green. The Type field shows On-demand, which indicates that the address binding was created for a PPP session. The Lease expiration field shows Infinite, which means that the binding is valid as long as the session is up. If a subnet must be released back to the leasing server while the session is still up, the session is reset so that it will be forced to obtain a new IP address. The Hardware address column for an On-demand entry shows the identifier for the session as detected by PPP. There are no bindings shown under the Bindings from all pools not associated with VRF field because the Global pool has not allocated any addresses.

Router# show ip dhcp binding  

Bindings from all pools not associated with VRF:

IP address       Hardware address        Lease expiration        Type

Bindings from VRF pool Green:

IP address       Hardware address        Lease expiration        Type

172.16.0.1       5674.312d.7465.7374.    Infinite                On-demand

                 2d38.3930.39

172.16.0.2       5674.312d.7465.7374.    Infinite                On-demand

                 2d38.3839.31

172.16.0.3       5674.312d.7465.7374.    Infinite                On-demand

                 2d36.3432.34

172.16.0.4       5674.312d.7465.7374.    Infinite                On-demand

                 2d38.3236.34

172.16.0.5       5674.312d.7465.7374.    Infinite                On-demand

                 2d34.3331.37

172.16.0.6       5674.312d.7465.7374.    Infinite                On-demand

                 2d37.3237.39

172.16.0.9       5674.312d.7465.7374.    Infinite                On-demand

                 2d39.3732.36

172.16.0.10      5674.312d.7465.7374.    Infinite                On-demand

                 2d31.3637

172.16.0.11      5674.312d.7465.7374.    Infinite                On-demand

                 2d39.3137.36

172.16.0.12      5674.312d.7465.7374.    Infinite                On-demand

                 2d37.3838.30

172.16.0.13      5674.312d.7465.7374.    Infinite                On-demand

                 2d32.3339.37

172.16.0.14      5674.312d.7465.7374.    Infinite                On-demand

                 2d31.3038.31

172.16.0.17      5674.312d.7465.7374.    Infinite                On-demand

                 2d38.3832.38

172.16.0.18      5674.312d.7465.7374.    Infinite                On-demand

                 2d32.3735.31

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Troubleshooting Tips

By default, the Cisco IOS DHCP server on which the ODAP manager is based attempts to verify an address availability by performing a ping operation to the address before allocation. The default DHCP ping configuration will wait for 2 seconds for an ICMP echo reply. This default configuration results in the DHCP server servicing one address request every 2 seconds. The number of ping packets being sent and the ping timeout are configurable. Thus, to reduce the address allocation time, you can reduce either the timeout or the number of ping packets sent. Reducing the timeout or the ping packets being sent will improve the address allocation time, at the cost of less ability to detect duplicate addresses.

Each ODAP will make a finite number of attempts (up to four retries) to obtain a subnet from DHCP or AAA. If these attempts are not successful, the subnet request from the pool automatically starts when there is another individual address request to the pool (for example, from a newly brought up PPP session). If a pool has not been allocated any subnets, you can force restarting the subnet request process by using the clear ip dhcp pool pool-name subnet * EXEC command.

Monitoring and Maintaining the ODAP

This task shows how to monitor and maintain the ODAP.

Note the following behavior for the clear ip dhcp binding, clear ip dhcp conflict, and clear ip dhcp subnet commands:

•If you do not specify the pool pool-name option and an IP address is specified, it is assumed that the IP address is an address in the global address space and will look among all the non-VRF DHCP pools for the specified binding/conflict/subnet.

•If you do not specify the pool pool-name option and the * option is specified, it is assumed that all automatic/ or on-demand bindings/conflicts/subnets in all VRF and non-VRF pools are to be deleted.

•If you specify both the pool pool-name option and the * option, all automatic or on-demand bindings/conflicts/subnets in the specified pool only will be cleared.

•If you specify the pool pool-name option and an IP address, the specified binding/conflict or the subnet containing the specified IP address will be deleted from the specified pool.

SUMMARY STEPS

1. enable

2. clear ip dhcp [pool pool-name] binding {* | address}

3. clear ip dhcp [pool pool-name] conflict {* | address}

4. clear ip dhcp [pool pool-name] subnet {* | address}

5. debug dhcp details

6. debug ip dhcp server events

7. show ip dhcp import

8. show ip interface [type number]

9. show ip dhcp pool pool-name

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	clear ip dhcp [pool pool-name] binding {* | address} Example: Router# clear ip dhcp binding *	Deletes an automatic address binding or objects from a specific pool from the DHCP server database.
Step 3	clear ip dhcp [pool pool-name] conflict {* | address} Example: Router# clear ip dhcp conflict *	Clears an address conflict or conflicts from a specific pool from the DHCP server database.
Step 4	clear ip dhcp [pool pool-name] subnet {* | address} Example: Router# clear ip dhcp subnet *	Clears all currently leased subnets in the named DHCP pool or all DHCP pools if name is not specified.
Step 5	debug dhcp details Example: Router# debug dhcp details	Monitors the subnet allocation/releasing in the on-demand address pools.
Step 6	debug ip dhcp server events Example: Router# debug ip dhcp server events	Reports DHCP server events, like address assignments and database updates.
Step 7	show ip dhcp import Example: Router# show ip dhcp import	Displays the option parameters that were imported into the DHCP server database.
Step 8	show ip interface [type number] Example: Router# show ip interface	Displays the usability status of interfaces configured for IP.
Step 9	show ip dhcp pool pool-name Example: Router# show ip dhcp pool green	Displays DHCP address pool information.

How to Configure DHCP ODAP Subnet Allocation Server Support

This procedure contains the following tasks:

•Configuring a Global Pool on a Subnet Allocation Server (required)

•Configuring a VRF Subnet Pool on a Subnet Allocation Server (optional)

•Using a VPN ID to Configure a VRF Subnet Pool on a Subnet Allocation Server (optional)

•Verifying the Subnet Allocation and DHCP Bindings (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

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip dhcp pool pool-name Example: Router(config)# ip dhcp pool GLOBAL-POOL	Enters DHCP pool configuration mode and specifies the subnet pool name.
Step 4	network network-number [mask | /prefix-length] Example: Router(dhcp-config)# network 10.0.0.0 255.255.255.0	Configures the subnet number and mask for a DHCP address pool on a Cisco IOS DHCP server. •The subnet mask or the prefix length can be configured in this step. The values that can be configured for the prefix-length argument follow CIDR bit count notation. The forward slash character must be used when configuring the prefix-length argument.
Step 5	subnet prefix-length prefix-length Example: Router(dhcp-config)# subnet prefix-length 8	Configures the subnet prefix length. The range of the prefix-length argument is from 1 to 31. •This command configures the number of IP addresses that each subnet is configured to allocate from the subnet pool. The values that can be configured for the prefix-length argument follow CIDR bit count notation format.

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

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip dhcp pool pool-name Example: Router(config)# ip dhcp pool VRF-POOL	Enters DHCP pool configuration mode and specifies the subnet pool name.
Step 4	vrf vrf-name Example: Router(dhcp-config)# vrf RED	Associates the on-demand address pool with a VPN routing and forwarding (VRF) instance name (or tag). •The vrf keyword and vrf-name argument are used to specify the VPN for the VRF pool. The vrf-name argument must match the VRF name (or tag) that is configured for the client.
Step 5	network network-number [mask |/prefix-length] Example: Router(dhcp-config)# network 10.1.1.0 /24	Configures the subnet number and mask for a DHCP address pool on a Cisco IOS DHCP server. •The subnet mask or the prefix length can be configured in this step. The values that can be configured for the prefix-length argument follow CIDR bit count notation. The forward slash character must be used when configuring the prefix-length argument.
Step 6	subnet prefix-length prefix-length Example: Router(dhcp-config)# subnet prefix-length 16	Configures the subnet prefix length. The range of the prefix-length argument is from 1 to 31. •This command configures the number of IP addresses that each subnet is configured to allocate from the subnet pool. The values that can be configured for the prefix-length argument follow CIDR bit count notation format.

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

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip vrf vrf-name Example: Router(config)#ip vrf RED	Creates a VRF routing table and specifies the VRF name (or tag). •The vrf-name argument must match the VRF name that is configured for the client and VRF pool in Step 9.
Step 4	rd route-distinguisher Example: Router(config-vrf)# rd 100:1	Creates routing and forwarding tables for a VRF instance created in Step 3. •There are two formats for configuring the route distinguisher argument. It can be configured in the as-number:network number (ASN:nn) format, as shown in the example, or it can be configured in the IP address:network number format (IP-address:nn).
Step 5	route-target both route-target-number Example: Router(config-vrf)# route-target both 100:1	Creates a route-target extended community for the VRF instance that was created in Step 3. •The both keyword is used to specify which routes should be imported and exported to the target VPN extended community (or the ODAP manager in this configuration). •The route-target-number argument follows the same format as the route-distinguisher argument in Step 4. These two arguments must match.
Step 6	vpn id vpn-id Example: Router(config-vrf)# vpn id 1234:123456	Configures the VPN ID. •This command is only used if the client (ODAP manager) is also configured with or assigned a VPN ID.
Step 7	exit Example: Router(config-vrf)# exit	Exits VRF configuration mode and enters global configuration mode.
Step 8	ip dhcp pool pool-name Example: Router(config)# ip dhcp pool VPN-POOL	Enters DHCP pool configuration mode and specifies the subnet pool name. •The VRF keyword and vrf-name argument are used to specify the VPN for the VRF pool. The vrf-name argument must match the VRF name (or tag) that is configured for the client.
Step 9	vrf vrf-name Example: Router(dhcp-config)#vrf RED	Associates the on-demand address pool with a VRF instance name. •The vrf-name argument must match the vrf-name argument that was configured in Step 3.
Step 10	network network-number [mask |/prefix-length] Example: Router(dhcp-config)# network 192.168.0.0 /24	Configures the subnet number and mask for a DHCP address pool on a Cisco IOS DHCP server. •The subnet mask or the prefix length can be configured in this step. The values that can be configured for the prefix-length argument follow CIDR bit count notation. The forward slash character must be used when configuring the prefix-length argument.
Step 11	subnet prefix-length prefix-length Example: Router(dhcp-config)# subnet prefix-length 16	Configures the subnet prefix length. •The range of the prefix-length argument is from 1 to 31. •This command configures the number of IP addresses that each subnet is configured to allocate from the subnet pool. The values that can be configured for the prefix-length argument follow CIDR bit count notation format.

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

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	show running-config | begin dhcp Example: Router# show running-config | begin dhcp	Used to display the local configuration of the router. •The configuration of the subnet prefix-length command will be displayed under the DHCP pools, for which subnet lease allocation has been configured. The subnet allocation size will be shown, following this command, in CIDR bit count notation. •The sample output is filtered with the begin keyword to start displaying output at the DHCP section of the running configuration.
Step 3	show ip dhcp pool [pool-name] Example: Router# show ip dhcp pool	Displays information about DHCP pools. •This command can be used to verify subnet allocation pool configuration on both the subnet allocation server and the ODAP manager. •The output of this command displays specific address pool information, including the name of the pool, utilization of address space, subnet size, number of total addresses, number of leased address, and pending events.
Step 4	show ip dhcp binding [ip-address] Example: Router# show ip dhcp binding	Displays information about DHCP bindings. •This command can be used to display subnet allocation to DHCP binding mapping information. •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.

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

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	debug dhcp [detail] Example: Router# debug dhcp detail	Displays debugging information about DHCP client activities and monitors the status of DHCP packets. •This example is issued with the detail keyword on the ODAP manager. The detail keyword is used to display and monitor the lease entry structure of the client and the state transitions of lease entries. This command also displays the values of the op, htype, hlen, hops, server identifier option, xid, secs, flags, ciaddr, yiaddr, siaddr, and giaddr fields of the DHCP packet that are shown in addition to the length of the options field.
Step 3	debug ip dhcp server {events | packets | linkage} Example: Router# debug ip dhcp server packets Router# debug ip dhcp server events	Enables DHCP server debugging. •This example is issued with the packets and events keywords on the subnet allocation server. The output displays lease transition and reception, as well as database information.

Configuration Examples for DHCP Server On-Demand Address Pool Manager

This section provides the following configuration examples:

•Defining DHCP ODAPs as the Global Default Mechanism: Example

•Defining DHCP ODAPs on an Interface: Example

•Configuring the DHCP Pool as an ODAP: Example

•Configuring the DHCP Pool as an ODAP for Non-MPLS VPNs: Example

•IPCP Subnet Mask Delivery: Example

•Configuring AAA and RADIUS: Example

•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

Defining DHCP ODAPs as the Global Default Mechanism: Example

The following example shows how to configure the on-demand address pooling mechanism to be used to serve an address request from a PPP client.

ip address-pool dhcp-pool

!

ip dhcp pool Green-pool

Defining DHCP ODAPs on an Interface: Example

The following example shows how to configure an interface to retrieve an IP address from an on-demand address pool:

interface Virtual-Template1

 ip vrf forwarding green

 ip unnumbered loopback1

 ppp authentication chap

 peer default ip address dhcp-pool

!

Configuring the DHCP Pool as an ODAP: Example

The following example shows two ODAPs configured to obtain their subnets from an external DHCP server:

Router# show run

Building configuration...

Current configuration : 3943 bytes

!

version 12.2

service timestamps debug uptime

service timestamps log uptime

no service password-encryption

!

hostname Router

!

no logging console

enable password lab

!

username vpn_green_net1 password 0 lab

username vpn_red_net1 password 0 lab

ip subnet-zero

!

ip dhcp pool green_pool

   vrf Green

   utilization mark high 60

   utilization mark low 40

   origin dhcp subnet size initial /24 autogrow /24

!

ip dhcp pool red_pool

   vrf Red

   origin dhcp

!

ip vrf Green

 rd 200:1

 route-target export 200:1

 route-target import 200:1

!

ip vrf Red

 rd 300:1

 route-target export 300:1

 route-target import 300:1

ip cef

ip address-pool dhcp-pool

!

no voice hpi capture buffer

no voice hpi capture destination 

!

interface Loopback0

 ip address 1.1.1.1 255.255.255.255

!

interface Loopback1

 ip vrf forwarding Green

 ip address 100.10.10.1 255.255.255.255

!

interface Loopback2

 ip vrf forwarding Red

 ip address 110.10.10.1 255.255.255.255

!

interface ATM2/0

 no ip address

 shutdown

 no atm ilmi-keepalive

!

interface ATM3/0

 no ip address

 no atm ilmi-keepalive

!

interface Ethernet4/0

 ip address 10.0.105.12 255.255.255.224

 duplex half

!

interface Ethernet4/1

 ip address 150.10.10.1 255.255.255.0

 duplex half

!

interface Ethernet4/2

 ip address 120.10.10.1 255.255.255.0

 duplex half

 tag-switching ip

!

interface Virtual-Template1

 ip vrf forwarding Green

 ip unnumbered Loopback1

 ppp authentication chap

!

interface Virtual-Template2

 ip vrf forwarding Green

 ip unnumbered Loopback1

 ppp authentication chap

!

interface Virtual-Template3

 ip vrf forwarding Green

 ip unnumbered Loopback1

 ppp authentication chap

!

interface Virtual-Template4

 ip vrf forwarding Red

 ip unnumbered Loopback2

 ppp authentication chap

!

interface Virtual-Template5

 ip vrf forwarding Red

 ip unnumbered Loopback2

 ppp authentication chap

!

interface Virtual-Template6

 ip vrf forwarding Red

 ip unnumbered Loopback2

 ppp authentication chap

!

router ospf 100

 log-adjacency-changes

 redistribute connected

 network 1.1.1.1 0.0.0.0 area 0

 network 120.10.10.0 0.0.0.255 area 0

 network 150.10.10.0 0.0.0.255 area 0

!

router bgp 100

 no synchronization

 bgp log-neighbor-changes

 neighbor 3.3.3.3 remote-as 100

 neighbor 3.3.3.3 update-source Loopback0

 !

 address-family ipv4 vrf Red

 redistribute connected

 redistribute static

 no auto-summary

 no synchronization

 network 110.0.0.0

 exit-address-family

 !

 address-family ipv4 vrf Green

 redistribute connected

 redistribute static

 no auto-summary

 no synchronization

 network 100.0.0.0

 exit-address-family

 !

 address-family vpnv4

 neighbor 3.3.3.3 activate

 neighbor 3.3.3.3 send-community extended

 exit-address-family

!

ip classless

ip route 172.19.0.0 255.255.0.0 10.0.105.1

no ip http server

ip pim bidir-enable

!

call rsvp-sync

!

mgcp profile default

!

dial-peer cor custom

!

gatekeeper

 shutdown

!

line con 0

 exec-timeout 0 0

line aux 0

line vty 0 4

 password lab

 login

!

end

Configuring the DHCP Pool as an ODAP for Non-MPLS VPNs: Example

The following example shows how to configure an interface to retrieve an IP address from an on-demand address pool. In this example, two non-VRF ODAPs are configured. There are two virtual-templates and two DHCP address pools, usergroup1 and usergroup2. Each virtual-template interface is configured to obtain IP addresses for the peer from the associated address pool.

!

ip dhcp pool usergroup1

 origin dhcp subnet size initial /24 autogrow /24

 lease 0 1

!

ip dhcp pool usergroup2

 origin dhcp subnet size initial /24 autogrow /24

 lease 0 1

!

interface virtual-template1

 ip unnumbered loopback1

 peer default ip address dhcp-pool usergroup1

!

interface virtual-template2

 ip unnumbered loopback1

 peer default ip address dhcp-pool usergroup2

IPCP Subnet Mask Delivery: Example

The following example shows a Cisco 827 router configured to use IPCP subnet masks:

Router# show run

 Building configuration...

 Current configuration :1479 bytes

 !

 version 12.2

 no service single-slot-reload-enable

 no service pad

 service timestamps debug datetime msec

 service timestamps log uptime

 no service password-encryption

 !

 hostname Router

 !

 no logging buffered

 logging rate-limit console 10 except errors

 !

 username 6400-nrp2 password 0 lab

 ip subnet-zero

 ip dhcp smart-relay

 !

 ip dhcp pool IPPOOLTEST

    import all

    origin ipcp

 !

 no ip dhcp-client network-discovery

 !

 interface Ethernet0

  ip address pool IPPOOLTEST

  ip verify unicast reverse-path

  hold-queue 32 in

 !

 interface ATM0

  no ip address

  atm ilmi-keepalive

  bundle-enable

  dsl operating-mode auto

  hold-queue 224 in

 !

 interface ATM0.1 point-to-point

  pvc 1/40 

   no ilmi manage

   encapsulation aal5mux ppp dialer

   dialer pool-member 1

  !

 !

 interface Dialer0

  ip unnumbered Ethernet0

  ip verify unicast reverse-path

  encapsulation ppp

  dialer pool 1

  dialer-group 1

  no cdp enable

  ppp authentication chap callin

  ppp chap hostname Router

  ppp chap password 7 12150415

  ppp ipcp accept-address

  ppp ipcp dns request

  ppp ipcp wins request

  ppp ipcp mask request

 !

 ip classless

 ip route 0.0.0.0 0.0.0.0 Dialer0

 no ip http server

 !

 dialer-list 1 protocol ip permit

 line con 0

  exec-timeout 0 0

  transport input none

  stopbits 1

 line vty 0 4

  login

 !

 scheduler max-task-time 5000

 end

Configuring AAA and RADIUS: Example

The following example shows one pool "Green" configured to obtain its subnets from the AAA (RADIUS) server located at IP address 172.16.1.1:

!

aaa new-model

!

aaa authorization configuration default group radius 

aaa accounting network default start-stop group radius

aaa session-id common

!

ip subnet-zero

!

ip dhcp ping packets 0

!

ip dhcp pool Green

   vrf Green

   utilization mark high 50

   utilization mark low 30

   origin aaa subnet size initial /28 autogrow /28

!

ip vrf Green

 rd 300:1

 route-target export 300:1

 route-target import 300:1

!

interface Ethernet1/1

 ip address 172.16.1.12 255.255.255.0

 duplex half

!

interface Virtual-Template1

 ip vrf forwarding Green

 no ip address

!

ip radius source-interface Ethernet1/1

!

!IP address of the RADIUS server host

radius-server host 172.16.1.1 auth-port 1645 acct-port 1646

radius-server retransmit 3

radius-server attribute 32 include-in-access-req 

radius-server attribute 44 include-in-access-req

radius-server key cisco

radius-server vsa send accounting

radius-server vsa send authentication

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-POOL

 network 10.0.0.0 255.255.255.0

 subnet 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-POOL 

 vrf RED

 network 172.16.0.0 /16

 subnet 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 RED

 rd 100:1

 route-target both 100:1 

 vpn id 1234:123456

 exit

 ip dhcp pool VPN-POOL

  vrf RED

  network 192.168.0.0 /24

  subnet prefix-length /27

  exit

Verifying 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 dhcp

ip dhcp pool GLOBAL-POOL

   network 10.0.0.0 255.255.255.0

   subnet 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-1

Pool ISP-1 :

 Utilization mark (high/low)    :100 / 0

 Subnet size (first/next)       :24 / 24 (autogrow)

 Total addresses                :0

 Leased addresses               :0

 Pending event                  :subnet request

 0 subnet is currently in the pool

The 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-ALLOC

Pool SUBNET-ALLOC :

 Utilization mark (high/low)    :100 / 0

 Subnet size (first/next)       :24 / 24 (autogrow)

 VRF name                       :RED

 Total addresses                :254

 Leased addresses               :0

 Pending event                  :none

 1 subnet is currently in the pool :

 Current index        IP address range                    Leased addresses

 10.0.0.1              10.0.0.1          - 10.0.0.254         0

Verifying 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 binding

Bindings from all pools not associated with VRF:

IP address          Client-ID/              Lease expiration        Type

                    Hardware address/

                    User name

10.0.0.0/26         0063.6973.636f.2d64.    Mar 29 2003 04:36 AM    Automatic

                    656d.6574.6572.2d47.

                    4c4f.4241.4c

Additional References

The following sections provide references related to configuring the DHCP ODAP manager.

Related Documents

Related Topic	Document Title
DHCP commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples	Cisco IOS IP Addressing and Services Command Reference, Release 12.4 T
DHCP conceptual information	"DHCP Overview" module
DHCP server configuration	"Configuring the Cisco IOS DHCP Server" module
DHCP client configuration	"Configuring the Cisco IOS DHCP Client" module
DHCP relay agent configuration	"Configuring the Cisco IOS DHCP Relay Agent" module
DHCP advanced features	"Configuring DHCP Services for Accounting and Security" module
DHCP enhancements for edge-session management	"Configuring DHCP Enhancements for Edge-Session Management" module
DHCP options	"DHCP Options" appendix in the Network Registrar User's Guide, Release 6.1.1

Standards

Standards	Title
No new or modified standards are supported by this functionality.	—

MIBs

MIBs	MIBs Link
No new or modified MIBs are supported by this feature.	To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: http://www.cisco.com/go/mibs

RFCs

RFCs	Title
RFC 951	Bootstrap Protocol (BOOTP)
RFC 1542	Clarifications and Extensions for the Bootstrap Protocol
RFC 2131	Dynamic Host Configuration Protocol
RFC 2685	Virtual Private Networks Identifier
RFC 3046	DHCP Relay Information Option

Technical Assistance

Description	Link
Technical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.	http://www.cisco.com/public/support/tac/home.shtml

Glossary

AAA—authentication, authorization, and accounting. Suite of network security services that provide the primary framework through which access control can be set up on your Cisco router or access server.

Cisco Access Registrar—A RADIUS server that supports service provider deployment of access services by centralizing AAA information and simplifying provisioning and management.

client—A host trying to configure its interface (obtain an IP address) using DHCP or BOOTP protocols.

DHCP—Dynamic Host Configuration Protocol.

incremental subnet size—The desired size of the second and subsequent subnets requested for an on-demand pool.

initial subnet size—The desired size of the first subnet requested for an on-demand pool.

IPCP—IP Control Protocol. Protocol that establishes and configures IP over PPP.

MPLS—Multiprotocol Label Switching. Emerging industry standard upon which tag switching is based.

ODAP—on-demand address pool.

PE router—provider edge router.

PPP—Point-to-Point Protocol.

RADIUS— Remote Authentication Dial-In User Service. Database for authenticating modem and ISDN connections and for tracking connection time.

relay agent—A router that forwards DHCP and BOOTP messages between a server and a client on different subnets.

releasable subnet—A leased subnet that has no address leased from it.

server—DHCP or BOOTP server.

VHG—Virtual Home Gateway. A Cisco IOS software component that terminates PPP sessions. It is owned and managed by the service provider on behalf of its customer to provide access to remote users of that customers network. A single service provider device (router) can host multiple VHGs of different customers. A VHG can be dynamically brought up and down based on the access pattern of the remote users. Note that there is no single IOS feature called the VHG; it is a collection of function and features.

VHG/PE router—A device that terminates PPP sessions and maps the remote users to the corresponding MPLS VPNs.

VPN—Virtual Private Network. Enables IP traffic to use tunneling to travel securely over a public TCP/IP network.

VPN information—In this document, VPN information refers to VRF name or VPN ID.

VRF—VPN routing and forwarding instance. A VRF consists of an IP routing table, a derived forwarding table, a set of interfaces that use the forwarding table, and a set of rules and routing protocols that determine what goes into the forwarding table. In general, a VRF includes the routing information that defines a customer VPN site that is attached to a PE router. Each VPN instantiated on the PE router has its own VRF.

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Note See Internetworking Terms and Acronyms for terms not included in this glossary.

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Feature Information for the DHCP Server On-Demand Address Pool Manager

Table 1 lists the features in this module and provides links to specific configuration information. Only features that were introduced or modified in Cisco IOS Releases 12.2(1) or a later release appear in the table.

Not all commands may be available in your Cisco IOS software release. For details on when support for specific commands was introduced, see the command reference documents.

For information on a feature in this technology that is not documented here, see the "DHCP Features Roadmap".

Cisco IOS software images are specific to a Cisco IOS software release, a feature set, and a platform. 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.

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Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

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Table 1 Feature Information for the DHCP On-Demand Address Pool Manager 

Feature Name	Releases	Feature Configuration Information
DHCP Server On-Demand Address Pool Manager for Non-MPLS VPNs	12.2(15)T 12.2(28)SB	This feature was enhanced to provide ODAP support for non-MPLS VPNs. The following section provides information about this feature: •How to Configure the DHCP Server On-Demand Address Pool Manager The following command was modified by this feature: peer default ip address
DHCP ODAP Server Support	12.2(15)T 12.2(28)SB	This feature introduces the capability to configure a DHCP server (or router) as a subnet allocation server. This capability allows the Cisco IOS DHCP server to be configured with a pool of subnets for lease to ODAP clients. The following section provides information about this feature: •How to Configure DHCP ODAP Subnet Allocation Server Support The following command was introduced by this feature: subnet prefix-length. The following command was modified by this feature: show ip dhcp binding.
DHCP Server On-Demand Address Pool Manager	12.2(8)T 12.28(SB)	The ODAP manager is 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 following section provides information about this feature: •How to Configure the DHCP Server On-Demand Address Pool Manager The following commands were introduced by this feature: aaa session-id, clear ip dhcp subnet, ip address pool, ip dhcp aaa default username, origin, show ip dhcp pool, utilization mark high, utilization mark low, vrf. The following commands were modified by this feature: clear ip dhcp binding, clear ip dhcp conflict, ip address-pool, peer default ip address.

Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.

Copyright © 2006 Cisco Systems, Inc. All rights reserved.
This module first published May 2, 2005. Last updated February 27, 2006.