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Table Of Contents
Configuring DHCP Enhancements for Edge-Session Management
Information About DHCP Enhancements for Edge-Session Management
On-Demand Address Pool Management
Design of the DHCP Enhancements for Edge-Session Management Feature
DHCP Server Co-Resident with the SG
DHCP Relay Agent Co-Resident with the SG
Benefits of the DHCP Enhancements for Edge-Session Management
How to Configure DHCP Enhancements for Edge-Session Management
Configuring the DHCP Address Pool and a Class Name
Configuring a Relay Pool with a Relay Source and Destination
Configuring a Relay Pool for a Remote DHCP Server
Configuring Other Types of Relay Pools
Configuring Relay Information for an Address Pool
Configuring Multiple Relay Sources for a Relay Pool
Configuration Examples for DHCP Enhancements for Edge Session Management
DHCP Address Range and Class Name Configuration: Example
DHCP Server Co-Resident with SG Configuration: Example
DHCP Relay Agent Co-Resident with SG Configuration: Example
Multiple DHCP Pools and Different ISPs Configuration: Example
Multiple Relay Sources and Destinations Configuration: Example
SG-Supplied Class Name Configuration: Example
Feature Information for DHCP Enhancements for Edge-Session Management
Configuring DHCP Enhancements for Edge-Session Management
The DHCP Enhancements for Edge-Session Management feature provides the capability of simultaneous service by multiple Internet Service Providers (ISPs) to customers using one network infrastructure. The end-user customer may change ISPs at any time.
The DHCP enhancements evolved out of the Service Gateways (SGs) requirement to receive information from the DHCP server about when client DISCOVER packets (session initiation) are received, when an address has been allocated to a client, and when a client has released a DHCP lease or the lease has expired (session termination).
Module History
This module was first published on March 29, 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 DHCP Enhancements for Edge-Session Management" section.
Contents
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Information About DHCP Enhancements for Edge-Session Management
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Information About DHCP Enhancements for Edge-Session Management
To configure the DHCP Enhancements for Edge-Session Management feature, you should understand the following concepts:
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DHCP Servers and Relay Agents
DHCP provides a framework for passing configuration information dynamically to hosts on a TCP/IP network. A DHCP client is an Internet host using DHCP to obtain configuration parameters such as an IP address.
A DHCP relay agent is any host that forwards DHCP packets between clients and servers. Relay agents are used to forward requests and replies between clients and servers when they are not on the same physical subnet. Relay agent forwarding is distinct from the normal forwarding of an IP router, where IP datagrams are switched between networks somewhat transparently. By contrast, relay agents receive DHCP messages and then generate a new DHCP message to send on another interface.
For more information, refer to the DHCP modules in the Cisco IOS IP Addressing Services Configuration Guide, Release 12.4.
On-Demand Address Pool Management
An On-Demand Address Pool (ODAP) is used to centralize the management of large pools of addresses and simplifies the configuration of large networks. ODAP provides a central management point for the allocation and assignment of IP addresses.
When a Cisco 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 Remote Authentication Dial-In User Service (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 and large-sized networks.
For more information, see the "Configuring the DHCP Server On-Demand Address Pool Manager" module.
Design of the DHCP Enhancements for Edge-Session Management Feature
With the DHCP Enhancements for Edge-Session Management feature, a DHCP server and relay agent are separate, but closely coupled. The basic design of the feature encompasses two types of configuration at the edge of an ISP network as follows:
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DHCP Server Co-Resident with the SG
With this configuration, the DHCP server is in the same device as the SG and allocates addresses from locally configured address pools or acquires a subnet of addresses to allocate from some other system in the network. There are no changes to the server address allocation function to support the configuration.
This configuration enables the DHCP server to notify the SG that it has received a broadcast sent by the end-user DHCP client. The SG passes the MAC address and other information to the DHCP server. The SG also passes a class name (for example, the name of the ISP), which is used by the DHCP server to match a pool-class definition.
Lease-state notifications are always made by the DHCP server to the SG, because the information is already present.
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DHCP Relay Agent Co-Resident with the SG
With this configuration, the relay agent is in the same device as the SG and intercedes in DHCP sessions to appear as the DHCP server to the DHCP client. As the server, the relay agent may obtain enough information about the DHCP session to notify the SG of all events (for example, lease termination).
Appearing to be the DHCP server is performed by using the DHCP functionality that is currently in use on unnumbered interfaces. This functionality enables the relay agent to substitute its own IP address for the server.
The packet is passed by the relay agent to the DHCP server and the SG is notified of the receipt. Following the notification, an inquiry is made by the relay agent to the SG about which DHCP class name to use. Then, the packet is passed by the relay agent to the selected DHCP server.
The end-user DHCP client MAC address and other pertinent information is passed to the SG. The SG returns the DHCP class name to use when matching a DHCP pool if the SG is configured to do so. If the DHCP relay agent is not acting as a server, it relays the packet to the DHCP server.
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Benefits of the DHCP Enhancements for Edge-Session Management
The benefits of the DHCP Enhancements for Edge-Session Management feature are as follows:
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How to Configure DHCP Enhancements for Edge-Session Management
This section contains the following procedures:
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Configuring the DHCP Address Pool and a Class Name
Perform this task to configure a DHCP server that assigns addresses from an address pool for a specific class name that has been assigned by an SG that is co-resident with the DHCP server at the edge.
If a DHCP server is resident in the same device as an SG and both are at the edge, a class name and address pool should be configured. In this case, the DHCP server notifies an SG of a DISCOVER broadcast received from a client and the SG returns a class name. The returned class name designates an address range of an address pool. The DHCP server sends the MAC address and IP address of the incoming interface or the specified relay-agent address to the SG.
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If dynamic allocation of the address pool is required using ODAP, the origin command is specified.
Prerequisites
The specification of the class name is required in the DHCP address-pool configuration and in the SG system itself to designate each DHCP client class name. A default class name should be configured if a user does not have one.
Each address pool should be associated with one or more DHCP classes (address-provider ISPs). When the DHCP client selects an ISP, the selection becomes the class name designated by the SG.
SUMMARY STEPS
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DETAILED STEPS
Step 1
enable
Example:Router> enable
Enables privileged EXEC mode.
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Step 2
configure terminal
Example:Router# configure terminal
Enters global configuration mode.
Step 3
ip dhcp pool name
Example:Router(config)# ip dhcp pool abc-pool
Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode. The name argument is the name of the pool and may either be a symbolic string (such as engineering) or an integer (such as 0).
Step 4
origin {dhcp | file url}
Example:Router(dhcp-config)# origin dhcp
(Optional) Configures an address pool as an On-Demand Address Pool (ODAP) or static mapping pool. The argument and keywords are as follows:
Step 5
network network-number [mask | prefix-length]
Example:Router(dhcp-config)# network 10.10.0.0 255.255.0.0
Configures the subnet number and mask for a DHCP address pool on a Cisco IOS DHCP server. The arguments are as follows:
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Step 6
class class-name
Example:Router(dhcp-config)# class abc-pool
Associates a class with a DHCP address pool and enters DHCP pool-class configuration mode. The class-name argument is the name of the class. It should match the DHCP address pool name.
Repeat this step to specify a default class name if required by the SG.
Step 7
address range start-ip end-ip
Example:Router(config-dhcp-pool-class)# address range 10.10.5.0 10.99.99.99
(Optional) Configures an IP address range from which the DHCP server would allocate the IP addresses. If an SG returned an IP address that is not configured, no action is taken.
This step enables the allocation of an address from a range for the class name specified in the previous step.
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Step 8
Repeat Steps 3, 5, and 6.
If there is an interface configured with multiple subnets and different ISPs, repeat this step to match the number of subnets. See the "Multiple DHCP Pools and Different ISPs Configuration: Example" section.
Step 9
exit
Example:Router(config-dhcp-pool-class)# exit
Exits to DHCP pool configuration mode.
Configuring a Relay Pool with a Relay Source and Destination
Perform this task to configure a relay pool when the DHCP relay and SG are resident in the same device at the edge, and all end users will obtain addresses from one pool. This task replaces the IP helper-address interface configuration.
If the SG notifies the relay agent that DHCP session notifications are required for a particular DHCP client, the relay agent will retain enough information about the DHCP session to notify the SG of all events (for example, lease termination). The relay intercedes DHCP sessions and assumes the role of the DHCP server. The IP address configuration becomes a dynamically changing value depending on the DHCP client information and the SG device policy information.
Restrictions
If a relay agent is interceding in DHCP sessions and assuming the role of the DHCP server, the use of DHCP authentication is not possible.
SUMMARY STEPS
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DETAILED STEPS
Step 1
enable
Example:Router> enable
Enables privileged EXEC mode.
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Step 2
configure terminal
Example:Router# configure terminal
Enters global configuration mode.
Step 3
ip dhcp pool name
Example:Router(config)# ip dhcp pool abc-pool
Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode. The name argument is the name of the pool and may either be a symbolic string (such as engineering) or an integer (such as 0). More than one name may be configured.
Step 4
update arp
Example:Router(dhcp-config)# update arp
(Optional) Configures secure and dynamic Address Resolution Protocol (ARP) entries in the ARP table to their corresponding DHCP bindings.
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Step 5
relay source ip-address subnet-mask
Example:Router(dhcp-config)# relay source 10.0.0.0 255.0.0.0
Configures the relay source. The ip-address and subnet-mask arguments are the IP address and subnet mask for the relay source.
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Step 6
relay destination [vrf vrf-name | global] ip-address
Example:Router(dhcp-config)# relay destination 10.5.5.0
Configures the IPv4 address of a remote DHCP server to which DHCP client packets are sent. The arguments and keywords are as follows:
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Step 7
accounting method-list-name
Example:Router(dhcp-config)# accounting RADIUS-GROUP1
(Optional) Enables DHCP accounting if the specified server group is configured to run RADIUS accounting.
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Step 8
exit
Example:Router(dhcp-config)# exit
Exits to global configuration mode.
Configuring a Relay Pool for a Remote DHCP Server
Perform this task to use an SG-supplied class name when selecting the remote DHCP server in a configured relay pool, which is used to specify how DHCP client packets should be relayed. Multiple configurations of relay targets may appear in a pool-class definition in which case all addresses are used for relay purposes.
Restrictions
The relay source command cannot be used with the network command or origin command since those commands implicitly designate the incoming interface and are used to define a different type of pool. It associates the relay only with an interface in the same way that the ip helper-address command does by its presence as an interface configuration command.
SUMMARY STEPS
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9.
DETAILED STEPS
Step 1
enable
Example:Router> enable
Enables privileged EXEC mode.
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Step 2
configure terminal
Example:Router# configure terminal
Enters global configuration mode.
Step 3
ip dhcp pool name
Example:Router(config)# ip dhcp pool abc-pool
Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode. The name argument is the name of the pool and may either be a symbolic string (such as engineering) or an integer (such as 0). You may specify more than one DHCP address pool.
Step 4
relay source ip-address subnet-mask
Example:Router(dhcp-config)# relay source 10.0.0.0 255.0.0.0
Configures the relay source. The ip-address and subnet-mask arguments are the IP address and subnet mask for the relay source.
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Step 5
relay destination [vrf vrf-name | global] ip-address
Example:Router(dhcp-config)# relay destination 10.5.5.0
Configures the IPv4 address of a remote DHCP server to which DHCP client packets are sent. The arguments and keywords are as follows:
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Step 6
accounting method-list-name
Example:Router(dhcp-config)# accounting RADIUS-GROUP1
(Optional) Enables DHCP accounting if the specified server group is configured to run RADIUS accounting.
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Step 7
class class-name
Example:Router(dhcp-config)# class abc-pool
Associates a class with a DHCP address pool and enters DHCP pool-class configuration mode. The class-name argument is the name of the class. You may configure more than one class name.
Step 8
relay target [vrf vrf-name | global] ip-address
Example:Router(config-dhcp-pool-class)# relay target 10.0.0.0
Configures the relay target IP address. The arguments and keywords are as follows:
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Step 9
exit
Example:Router(config-dhcp-pool-class)# exit
Exits to DHCP pool configuration mode.
Configuring Other Types of Relay Pools
This section contains the following procedures:
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Configuring Relay Information for an Address Pool
Perform this task to configure relay information for an address pool. In this configuration, the SG sends one class name that results in the DISCOVER packet being relayed to a server at the IP address configured using the relay target command. If the SG sends a class name that is not configured as being associated with the address pool, then no action is taken.
Restrictions
Specifying the address range command and relay target command in a pool-class definition is not possible, because this would allocate an address and relay for the same packet.
SUMMARY STEPS
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DETAILED STEPS
Configuring Multiple Relay Sources for a Relay Pool
Perform this task to configure multiple relay sources for a relay pool. The configuration is similar to configuring an IP helper address on multiple interfaces. Pools are matched to the IP addresses on an incoming interface in the order in which the interfaces display when the show running-config command is used. Once a relay is found or an address allocation is found, the search stops.
SUMMARY STEPS
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DETAILED STEPS
Step 1
enable
Example:Router> enable
Enables privileged EXEC mode.
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Step 2
configure terminal
Example:Router# configure terminal
Enters global configuration mode.
Step 3
interface type number
Example:Router(config)# interface ethernet1
Configures an interface and enters interface configuration mode. The arguments are as follows:
Step 4
ip address ip-address mask [secondary]
Example:Router(config-if)# ip address 10.0.0.0 255.0.0.0
Sets a primary or secondary IP address for an interface.
Step 5
exit
Example:Router(config-if)# exit
Exits to global configuration mode.
Step 6
ip dhcp pool name
Example:Router(config)# ip dhcp pool abc-pool1
Configures a DHCP address pool on a DHCP server and enters DHCP pool configuration mode. The name argument is the name of the pool and may either be a symbolic string (such as engineering) or an integer (such as 0). More than one pool may be assigned.
Step 7
relay source ip-address subnet-mask
Example:Router(dhcp-config)# relay source 10.0.0.0 255.0.0.0
Configures the relay source. The ip-address and subnet-mask arguments are the IP address and subnet mask for the relay source.
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Step 8
relay destination [vrf vrf-name | global] ip-address
Example:Router(dhcp-config)# relay destination 10.5.5.0
Configures the IPv4 address of a remote DHCP server to which DHCP client packets are sent. The arguments and keywords are as follows:
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Step 9
accounting method-list-name
Example:Router(dhcp-config)# accounting RADIUS-GROUP1
(Optional) Enables DHCP accounting if the specified server group is configured to run RADIUS accounting.
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Step 10
Repeat Steps 6 and 7 for each configured DHCP pool.
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Step 11
exit
Example:Router(dhcp-config)# exit
Exits to global configuration mode.
Configuration Examples for DHCP Enhancements for Edge Session Management
This section provides the following configuration examples:
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DHCP Address Range and Class Name Configuration: Example
The following example shows how to configure an address range for a particular network and class name for a DHCP pool.
ip dhcp pool abc-poolnetwork 10.10.0.0 255.255.0.0class abc-pooladdress range 10.10.5.0 10.10.5.99DHCP Server Co-Resident with SG Configuration: Example
In the following example, the ISPs are ABC and DEF companies. The ABC company has its addresses assigned from an address pool that is dynamically allocated using ODAP. The DEF company has its customer addresses assigned from the address pool 10.100.0.0/16. Customers not associated with any ISP will have an address allocated from the address pool 10.1.0.0/16 and the lease time is set to 10 minutes.
!Interface configurationinterface ethernet1ip address 10.20.0.1. 255.255.0.0ip address 10.1.0.1 255.255.0.0 secondaryip address 10.100.0.1 255.255.0.0 secondary!Address pool for ABC customersip dhcp pool abc-poolnetwork 20.1.0.0 255.255.0.0class abc!!Address pool for DEF customersip dhcp pool def-poolnetwork 10.100.0.0 255.255.0.0class def!Address pool for customers without an ISPip dhcp pool tempnetwork 10.1.0.0 255.255.0.0lease 0 0 10class defaultDHCP Relay Agent Co-Resident with SG Configuration: Example
In the following example, there are two ISPs: abcpool and defpool. The abcpool ISP and its customers are allowed to have addresses in the ranges 10.1.0.0/16 and 30.1.0.0/16 and are relayed to the DHCP server at 10.55.10.1. The defpool ISP and its customers are allowed to have addresses in the ranges 20.1.0.0/16 and 40.4.0.0/16 and are relayed to the DHCP server at 12.10.2.1.
!Address ranges:interface ethernet1ip address 10.1.0.0 255.255.0.0ip address 10.2.0.0 255.255.0.0 secondaryinterface ethernet2ip address 10.3.0.0 255.255.0.0ip address 10.4.0.0 255.255.0.0 secondary!Address pools for abcpool1 and abcpool2:ip dhcp pool abcpool1relay source 10.1.0.0 255.255.0.0class abcpoolrelay target 10.5.10.1!Address pool for abcpool2:ip dhcp pool abcpool2relay source 10.1.0.0 255.255.0.0class abcpoolrelay target 10.55.10.1!Address pools for defpool1 and defpool2:ip dhcp pool defpool1relay source 10.1.0.0 255.255.0.0class defpoolrelay target 10.10.2.1ip dhcp pool defpool2relay source 10.4.0.0 255.255.0.0class defpoolrelay target 10.10.2.1Multiple DHCP Pools and Different ISPs Configuration: Example
The following example shows how to configure one interface and multiple DHCP pools that have different ISPs by using the network command.
interface ethernet1ip address 10.0.0.1 255.0.0.0ip address 10.1.0.1 255.0.0.0!ip dhcp pool xnetwork 10.0.0.0 255.0.0.0class ISP1!ip dhcp pool ynetwork 10.1.0.0 255.0.0.0class ISP2Multiple Relay Sources and Destinations Configuration: Example
In the following example, multiple relay sources and destinations may be configured for a relay pool. This is similar the ip helper-address configuration on multiple interfaces. Pools are matched to the (possibly multiple) IP addresses on an incoming interface in the order in which they appear when using the show running-config command to display information about that interface. Once either a relay is found or an address allocation is found, the search stops. For example, given the following configuration:
interface ethernet1ip address 10.0.0.1 255.0.0.0ip address 10.0.0.5 255.0.0.0 secondaryip dhcp pool xrelay source 10.0.0.0 255.0.0.0relay destination 10.0.0.1ip dhcp pool yrelay source 10.0.0.0 255.0.0.0relay destination 10.0.0.1In the following example, the DHCP client packet would be relayed to 10.0.0.1, if the SG specified ISP1 as the class name, and would be relayed to 10.0.0.5, if the SG specified ISP2 as the class name.
interface ethernet1ip address 10.0.0.1 255.0.0.0ip address 10.0.0.5 255.0.0.0 secondaryip dhcp pool xrelay source 10.0.0.0 255.0.0.0relay destination 10.2.0.0 255.0.0.0class ISP1relay target 10.0.0.1class ISP2relay target 10.0.0.5SG-Supplied Class Name Configuration: Example
In the following example, an SG-supplied class name is to be used in selecting the remote DHCP server to which packets should be relayed.
ip dhcp pool abc-pool-1relay source 10.1.0.0 255.255.0.0relay destination 10.1.0.0class classname1relay target 10.20.10.1class classname2relay target 10.0.10.1class classname3In the example above, an SG-supplied class name, called classname1, would relay the DHCP DISCOVER packet to the server at the relay target IP address 10.20.10.1, while SG classname2 would relay the DHCP DISCOVER packet to the server at the relay target IP address 10.0.10.1. This configuration relays the packet to destination IP address 10.0.0.1, because the pool matches the first configured address on the interface. If the SG returns a classname3, then the default pool is the default address specified as the relay destination. If the SG returns any class name other than classname1, classname2, or classname3, then no relay action is taken.
Additional References
The following sections provide references related to configuring DHCP Enhancements for Edge-Session Management.
Related Documents
Standards
MIBs
RFCs
Technical Assistance
Feature Information for DHCP Enhancements for Edge-Session Management
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 Release 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 a specific command was introduced, see the command reference documentation.
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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Table 1 Feature Information for DHCP Enhancements for Edge-Session Management
DHCP Relay Accounting
12.4(6)T
The DHCP Relay Accounting feature allows a Cisco IOS DHCP relay agent to send a RADIUS accounting start packet when an address is assigned to a client and a RADIUS accounting stop packet when the address is released. This feature is enabled by using the accounting command with relay pools that use the relay destination command in DHCP pool configuration mode.
The following sections provide information about this feature:
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No new commands were introduced by this feature.
DHCP Enhancements for Edge-Session Management
12.3(14)T
12.2(28)SB
The DHCP Enhancements for Edge-Session Management feature provides the capability of simultaneous service by multiple ISPs to customers using one network infrastructure. The end-user customer may change ISPs at any time.
All sections in this module provide information about this feature.
The following commands were introduced by this feature: relay destination, relay source, and relay target.
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 March 29, 2005. Last updated February 27, 2006.
