Pool Primary Site Assignment

Table Of Contents

Configuring the Cisco IOS DHCP Server

Contents

Prerequisites for Configuring the DHCP Server

Information About the Cisco IOS DHCP Server

Overview of the DHCP Server

DHCP Server Address Allocation Using Option 82

How to Configure the Cisco IOS DHCP Server

Configuring a DHCP Database Agent or Disabling Conflict Logging

Database Agents

Address Conflicts

Restrictions

Excluding IP Addresses

Configuring a DHCP Address Pool

DHCP Address Pool Conventions

DHCP Address Pool Selection

DHCP Server Address Pool with Multiple Disjoint Subnets

Prerequisites

Restrictions

Configuring Manual Bindings

Address Bindings

Restrictions

Troubleshooting Tips

Configuring DHCP Static Mapping

DHCP Database

Creating the Static Mapping Text File

Configuring the DHCP Server to Read a Static Mapping Text File

Examples

Customizing DHCP Server Operation

Ping Packet Settings

Option to Ignore All BOOTP Requests

Configuring a Remote Router to Import DHCP Server Options from a Central DHCP Server

Configuring the Central DHCP Server to Update DHCP Options

Configuring the Remote Router to Import DHCP Options

Configuring DHCP Address Allocation Using Option 82

DHCP Address Allocation Using Option 82 Feature Design

Usage Scenario for DHCP Address Allocation Using Option 82

DHCP Class Capability

Restrictions for DHCP Address Allocation Using Option 82

Enabling Option 82 for DHCP Address Allocation

Troubleshooting Tips

Defining the DHCP Class and Relay Agent Information Patterns

Prerequisites

Troubleshooting Tips

Defining the DHCP Address Pool

Configuring a Static Route with the Next-Hop Dynamically Obtained Through DHCP

Prerequisites

Restrictions

Clearing DHCP Server Variables

Configuration Examples for the Cisco IOS DHCP Server

DHCP Database Agent Configuration: Example

DHCP Address Pool Configuration: Example

DHCP Address Pool Configuration with Multiple Disjoint Subnets: Example

Excluding IP Addresses: Example

Manual Bindings Configuration: Example

Static Mapping Configuration: Example

Option to Ignore all BOOTP Requests: Example

DHCP Server Options Import: Example

DHCP Address Allocation Using Option 82: Example

Static Routes Using a DHCP Default Gateway: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for the Cisco IOS DHCP Server


Configuring the Cisco IOS DHCP Server


Cisco routers running Cisco IOS software include Dynamic Host Configuration Protocol (DHCP) server and relay agent software. The Cisco IOS DHCP server is a full DHCP server implementation that assigns and manages IP addresses from specified address pools within the router to DHCP clients. The DHCP server can be configured to assign additional parameters such as the IP address of the domain name system (DNS) server and the default router.

This module describes the concepts and the tasks needed to configure the Cisco IOS DHCP server.

Module History

This module was first published on May 2, 2005, and last updated on June 28, 2007.

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 Cisco IOS DHCP Server" section.

Contents

Prerequisites for Configuring the DHCP Server

Information About the Cisco IOS DHCP Server

How to Configure the Cisco IOS DHCP Server

Configuration Examples for the Cisco IOS DHCP Server

Additional References

Feature Information for the Cisco IOS DHCP Server

Prerequisites for Configuring the DHCP Server

Before you configure the Cisco IOS DHCP server, you should understand the concepts documented in the "DHCP Overview" module.

The Cisco IOS DHCP server and relay agent are enabled by default. You can verify if they have been disabled by checking your configuration file. If they have been disabled, the no service dhcp command will appear in the configuration file. Use the service dhcp command to reenable the functionality if necessary.

The Cisco IOS DHCP relay agent will be enabled on an interface only when the ip helper-address is configured. This command enables the DHCP broadcast to be forwarded to the configured DHCP server.

Information About the Cisco IOS DHCP Server

Before you configure the DHCP server, you should understand the following concepts:

Overview of the DHCP Server

DHCP Server Address Allocation Using Option 82

Overview of the DHCP Server

The Cisco IOS DHCP server accepts address assignment requests and renewals and assigns the addresses from predefined groups of addresses contained within DHCP address pools. These address pools can also be configured to supply additional information to the requesting client such as the IP address of the DNS server, the default router, and other configuration parameters. The Cisco IOS DHCP server can accept broadcasts from locally attached LAN segments or from DHCP requests that have been forwarded by other DHCP relay agents within the network.

DHCP Server Address Allocation Using Option 82

The Cisco IOS DHCP server can allocate dynamic IP addresses based on the relay information option (option 82) information sent by the relay agent.

Automatic DHCP address allocation is typically based on an IP address, whether it be the gateway address (giaddr field of the DHCP packet) or the incoming interface IP address. In some networks, it is necessary to use additional information to further determine which IP addresses to allocate. By using option 82, the Cisco IOS relay agent has long been able to include additional information about itself when forwarding client-originated DHCP packets to a DHCP server. The Cisco IOS DHCP server can also use option 82 as a means to provide additional information to properly allocate IP addresses to DHCP clients.

How to Configure the Cisco IOS DHCP Server

This section contains the following tasks:

Configuring a DHCP Database Agent or Disabling Conflict Logging (required)

Excluding IP Addresses (optional)

Configuring a DHCP Address Pool (required)

Configuring Manual Bindings (optional)

Configuring DHCP Static Mapping (optional)

Customizing DHCP Server Operation (optional)

Configuring a Remote Router to Import DHCP Server Options from a Central DHCP Server (optional)

Configuring DHCP Address Allocation Using Option 82 (optional)

Configuring a Static Route with the Next-Hop Dynamically Obtained Through DHCP (optional)

Clearing DHCP Server Variables (optional)

Configuring a DHCP Database Agent or Disabling Conflict Logging

Perform this task to configure a DHCP database agent.

Database Agents

A DHCP database agent is any host (for example, an FTP, TFTP, or rcp server) or storage media on the DHCP server (for example, disk0) that stores the DHCP bindings database. You can configure multiple DHCP database agents, and you can configure the interval between database updates and transfers for each agent.

Automatic bindings are IP addresses that have been automatically mapped to the MAC addresses of hosts that are found in the DHCP database. Automatic binding information (such as lease expiration date and time, interface index, and VPN routing and forwarding [VRF] name) is stored on a database agent. The bindings are saved as text records for easy maintenance.

Address Conflicts

An address conflict occurs when two hosts use the same IP address. During address assignment, DHCP checks for conflicts using ping and gratuitous Address Resolution Protocol (ARP). If a conflict is detected, the address is removed from the pool. The address will not be assigned until the administrator resolves the conflict.

Restrictions

We strongly recommend using database agents. However, the Cisco IOS server can run without them. If you choose not to configure a DHCP database agent, disable the recording of DHCP address conflicts on the DHCP server by using the no ip dhcp conflict logging command in global configuration mode. If there is conflict logging but no database agent configured, bindings are lost across router reboots. Possible false conflicts can occur causing the address to be removed from the address pool until the network administrator intervenes.

SUMMARY STEPS

1. enable

2. configureterminal

3. ip dhcp database url [timeout seconds |write-delay seconds]
or
no ip dhcp conflict logging

DETAILED STEPS

 

Command or Action

Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

ip dhcp database url [timeoutseconds | write-delayseconds]

or

no ip dhcp conflict logging

Example:

Router(config)# ip dhcp database ftp://user:password@172.16.1.1/router-dhcp timeout 80

or

Example:

Router(config)# no ip dhcp conflict logging

Configures a DHCP server to save automatic bindings on a remote host called a database agent.

or

Disables DHCP address conflict logging.

Choose this option only if you do not configure a DHCP database agent. See the "Restrictions" section for guidelines.

Excluding IP Addresses

Perform this task to specify IP addresses (excluded addresses) that the DHCP server should not assign to clients.

The IP address configured on the router interface is automatically excluded from the DHCP address pool. The DHCP server assumes that all other IP addresses in a DHCP address pool subnet are available for assigning to DHCP clients.

You need to exclude addresses from the pool if the DHCP server should not allocate those IP addresses. An example usage scenario is when two DHCP servers are set up to service the same network segment (subnet) for redundancy. If the two DHCP servers do not coordinate their services with each other using a protocol such as DHCP failover, then each DHCP server must be configured to allocate from a non-overlapping set of addresses in the shared subnet. See the "Excluding IP Addresses: Example" for a configuration example.

SUMMARY STEPS

1. enable

2. configureterminal

3. ip dhcp excluded-address low-address [high-address]

DETAILED STEPS

 

Command or Action

Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

ip dhcp excluded-address low-address [high-address]

Example:

Router(config)# ip dhcp excluded-address 172.16.1.100 172.16.1.103

Specifies the IP addresses that the DHCP server should not assign to DHCP clients.

Configuring a DHCP Address Pool

Perform this task to configure a DHCP address pool. On a per-address pool basis, specify DHCP options for the client as necessary.

DHCP Address Pool Conventions

You can configure a DHCP address pool with a name that is a symbolic string (such as "engineering") or an integer (such as 0). Configuring a DHCP address pool also puts the router into DHCP pool configuration mode—identified by the (dhcp-config)# prompt—from which you can configure pool parameters (for example, the IP subnet number and default router list).

DHCP Address Pool Selection

DHCP defines a process by which the DHCP server knows the IP subnet in which the DHCP client resides, and it can assign an IP address from a pool of valid IP addresses in that subnet. The process by which the DHCP server identifies which DHCP address pool to use to service a client request is described in the "DHCP Address Pool Selection" section.

The DHCP server identifies which DHCP address pool to use to service a client request as follows:

If the client is not directly connected (the giaddr field of the DHCPDISCOVER broadcast message is non-zero), the DHCP server matches the DHCPDISCOVER with a DHCP pool that has the subnet that contains the IP address in the giaddr field.

If the client is directly connected (the giaddr field is zero), the DHCP server matches the DHCPDISCOVER with DHCP pool(s) that contain the subnet(s) configured on the receiving interface. If the interface has secondary IP addresses, the subnets associated with the secondary IP addresses are examined for possible allocation only after the subnet associated with the primary IP address (on the interface) is exhausted.

Cisco IOS DHCP server software supports advanced capabilities for IP address allocation. See the "Configuring DHCP Address Allocation Using Option 82" section for more information.

DHCP Server Address Pool with Multiple Disjoint Subnets

For any DHCP pool, you can configure a primary subnet and any number of secondary subnets. Each subnet is a range of IP addresses that the router uses to allocate an IP address to a DHCP client. The DHCP server multiple subnet functionality enables a Cisco IOS DHCP server address pool to manage additional IP addresses by adding the addresses to a secondary subnet of an existing DHCP address pool (instead of using a separate address pool).

Secondary Subnet Conventions

Configuring a secondary DHCP subnetwork places the router in DHCP pool secondary subnet configuration mode—identified by the (config-dhcp-subnet-secondary)# prompt—from which you can configure a default address list that is specific to the secondary subnet.

IP Address Allocation from a DHCP Server Address Pool with Secondary Subnets

If the DHCP server selects an address pool that contains multiple subnets, the DHCP server allocates an IP address from the subnets as follows:

When the DHCP server receives an address assignment request, it looks for a free address in the primary subnet.

When the primary subnet is exhausted, the DHCP server automatically looks for a free address in any secondary subnets maintained by the DHCP server (even though the giaddr does not necessarily match the secondary subnet). The server inspects the subnets for address availability in the order in which the subnets were added to the pool.

If the giaddr matches a secondary subnet in the pool, the DHCP server allocates an IP address from that secondary subnet (even if IP addresses are available in the primary subnet and irrespective of the order in which secondary subnets where added).

Prerequisites

Before you configure the DHCP address pool, you need to:

Identify DHCP options for devices where necessary, including the following:

Default boot image name

Default routers

Domain Name System (DNS) servers

NetBIOS name server

Primary subnet

Secondary subnets and subnet-specific default router lists

Decide on a NetBIOS node type (b, p, m, or h).

Decide on a DNS domain name.

Restrictions

You cannot configure manual bindings within the same pool that is configured with the network DHCP pool configuration command. To configure manual bindings, see the "Configuring Manual Bindings" section.

SUMMARY STEPS

1. enable

2. configureterminal

3. ip dhcp pool name

4. network network-number [mask | /prefix-length]

5. domain-namedomain

6. dns-serveraddress [address2 ... address8]

7. bootfile filename

8. next-server address [address2 ... address8]

9. netbios-name-serveraddress [address2 ... address8]

10. netbios-node-typetype

11. default-router address [address2 ... address8]

12. optioncode[instancenumber] {asciistring | hexstring | ip-address}

13. lease {days[hours][minutes]|infinite}

14. network network-number [{mask | /prefix-length} [secondary]]

15. override default-routeraddress [address2 ... address8]

16. end

17. show ip dhcp binding[address]

18. show ip dhcp conflict[address]

19. show ip dhcp database[url]

20. show ip dhcp server statistics

DETAILED STEPS

 

Command or Action

Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

ip dhcp pool name

Example:

Router(config)# ip dhcp pool 1

Creates a name for the DHCP server address pool and enters DHCP pool configuration mode.

Step 4 

network network-number [mask | /prefix-length]

Example:

Router(dhcp-config)# network 172.16.0.0 /16

Specifies the subnet network number and mask of the DHCP address pool.

Step 5 

domain-name domain

Example:

Router(dhcp-config)# domain-name cisco.com

Specifies the domain name for the client.

Step 6 

dns-server address [address2 ... address8]

Example:

Router(dhcp-config)# dns server 172.16.1.103 172.16.2.103

Specifies the IP address of a DNS server that is available to a DHCP client.

One IP address is required; however, you can specify up to eight IP addresses in one command line.

Servers should be listed in order of preference.

Step 7 

bootfile filename

Example:

Router(dhcp-config)# bootfile xllboot

(Optional) Specifies the name of the default boot image for a DHCP client.

The boot file is used to store the boot image for the client. The boot image is generally the operating system the client uses to load.

Step 8 

next-server address [address2 ... address8]

Example:

Router(dhcp-config)# next-server 172.17.1.103 172.17.2.103

(Optional) Configures the next server in the boot process of a DHCP client.

If multiple servers are specified, DHCP assigns them to clients in round-robin order. The first client gets address 1, the next client gets address 2, and so on.

If this command is not configured, DHCP uses the server specified by the ip helper address command as the boot server.

Step 9 

netbios-name-server address [address2 ... address8]

Example:

Router(dhcp-config)# netbios-name-server 172.16.1.103 172.16.2.103

(Optional) Specifies the NetBIOS Windows Internet Naming Service (WINS) server that is available to a Microsoft DHCP client.

One address is required; however, you can specify up to eight addresses in one command line.

Servers should be listed in order of preference.

Step 10 

netbios-node-type type

Example:

Router(dhcp-config)# netbios-node-type h-node

(Optional) Specifies the NetBIOS node type for a Microsoft DHCP client.

Step 11 

default-router address [address2 ... address8]

Example:

Router(dhcp-config)# default-router 172.16.1.100 172.16.1.101

(Optional) Specifies the IP address of the default router for a DHCP client.

The IP address should be on the same subnet as the client.

One IP address is required; however, you can specify a up to eight IP addresses in one command line. These default routers are listed in order of preference; that is, address is the most preferred router, address2 is the next most preferred router, and so on.

When a DHCP client requests an IP address, the router—acting as a DHCP server—accesses the default router list to select another router that the DHCP client is to use as the first hop for forwarding messages. After a DHCP client has booted, the client begins sending packets to its default router.

Step 12 

option code[instancenumber] {asciistring | hexstring | ip-address}

Example:

Router(dhcp-config)# option 19 hex 01

(Optional) Configures DHCP server options.

Step 13 

lease {days [hours] [minutes]| infinite}

Example:

Router(dhcp-config)# lease 30

(Optional) Specifies the duration of the lease.

The default is a one-day lease.

The infinite keyword specifies that the duration of the lease is unlimited.

Step 14 

networknetwork-number [{mask | /prefix-length} [secondary]]

Example:

Router(dhcp-config)# network 10.10.0.0 255.255.0.0 secondary

(Optional) Specifies the network number and mask of a secondary DHCP server address pool. Any number ofsecondary subnets can be added to the DHCP server address pool.

During execution of this command, the configuration mode changes to DHCP pool secondary subnet configuration mode, which is identified by the (config-dhcp-subnet-secondary)# prompt. In this mode, the administrator can configure a default router list that is specific to the subnet.

Step 15 

override default-routeraddress [address2 ... address8]

Example:

Router(config-dhcp-subnet-secondary)# override default-router 10.10.0.100 10.10.0.101

(Optional) Specifies the default router list that is used when an IP address is assigned to a DHCP client from this secondary subnet.

If this subnet-specific override value is configured, it is used when assigning an IP address from the subnet; the network-wide default router list is used only to set the gateway router for the primary subnet.

If this subnet-specific override value is not configured, the network-wide default router list is used when assigning an IP address from the subnet.

Step 16 

end

Example:

Router(dhcp-config)# end

Returns to global configuration mode.

Step 17 

show ip dhcp binding [address]

Example:

Router# show ip dhcp binding

(Optional) Displays a list of all bindings created on a specific DHCP server.

Use the show ip dhcp binding command to display the IP addresses that have already been assigned. Verify that the address pool has not been exhausted. If necessary, re-create the pool to create a larger pool of addresses.

Use the show ip dhcp binding command to display the lease expiration date and time of the IP address of the host.

Step 18 

show ip dhcp conflict [address]

Example:

Router# show ip dhcp conflict

(Optional) Displays a list of all address conflicts.

Step 19 

show ip dhcp database [url]

Example:

Router# show ip dhcp database

(Optional) Displays recent activity on the DHCP database.

Step 20 

show ip dhcp server statistics

Example:

Router# show ip dhcp server statistics

(Optional) Displays count information about server statistics and messages sent and received.

Configuring Manual Bindings

Perform this task to configure manual bindings.

Address Bindings

An address binding is a mapping between the IP address and MAC address of a client. The IP address of a client can be assigned manually by an administrator or assigned automatically from a pool by a DHCP server.

Manual bindings are IP addresses that have been manually mapped to the MAC addresses of hosts that are found in the DHCP database. Manual bindings are stored in NVRAM on the DHCP server. Manual bindings are just special address pools. There is no limit on the number of manual bindings, but you can only configure one manual binding per host pool.

Automatic bindings are IP addresses that have been automatically mapped to the MAC addresses of hosts that are found in the DHCP database. Because the bindings are stored in volatile memory on the DHCP server, binding information is lost in the event of a power failure or upon router reload for any other reason. To prevent the loss of automatic binding information in such an event, a copy of the automatic binding information can be stored on a remote host called a DHCP database agent. The bindings are periodically written to the database agent. If the router reloads, the bindings are read back from the database agent to the DHCP database on the DHCP server.


Note We strongly recommend using database agents. However, the Cisco IOS DHCP server can function without database agents.


All DHCP clients send a client identifier (DHCP option 61) in the DHCP packet. To configure manual bindings, you must enter the client-identifier DHCP pool configuration command with the appropriate hexadecimal values identifying the DHCP client.

Restrictions

You cannot configure manual bindings within the same pool that is configured with the network command in DHCP pool configuration mode. See the "Configuring a DHCP Address Pool" section for information about DHCP address pools and the network command.

SUMMARY STEPS

1. enable

2. configureterminal

3. ip dhcp pool pool-name

4. host address[mask |/prefix-length]

5. client-identifier unique-identifier

6. hardware-address hardware-address type

7. client-name name

DETAILED STEPS

 

Command or Action

Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

ip dhcp pool pool-name

Example:

Router(config)# ip dhcp pool pool1

Creates a name for the DHCP server address pool and places you in DHCP pool configuration mode—identified by the (dhcp-config)# prompt.

Step 4 

host address[mask |/prefix-length]

Example:

Router(dhcp-config)# host

Specifies the IP address and subnet mask of the client.

There is no limit on the number of manual bindings but you can only configure one manual binding per host pool.

Step 5 

client-identifier unique-identifier

Example:

Router(dhcp-config)# client-identifier01b7.0813.8811.66

Specifies the unique identifier for DHCP clients. This command is used for DHCP requests.

DHCP clients require client identifiers. The unique identification of the client is specified in dotted hexadecimal notation, for example, 01b7.0813.8811.66, where 01 represents the Ethernet media type.

See "Troubleshooting Tips" below for information on how to determine the client identifier of the DHCP client.

Step 6 

hardware-address hardware-address type

Example:

Router(dhcp-config)# hardware-addressb708.1388.f166 ieee802

(Optional) Specifies a hardware address for the client. This command is used for BOOTP requests.

Step 7 

client-namename

Example:

Router(dhcp-config)#client-nameclient1

(Optional) Specifies the name of the client using any standard ASCII character.

The client name should not include the domain name. For example, the name mars should not be specified as mars.cisco.com.

Troubleshooting Tips

You can determine the client identifier by using the debug ip dhcp server packet command. In the following example, the client is identified by the value 0b07.1134.a029.

Router# debug ip dhcp server packet
DHCPD:DHCPDISCOVER received from client 0b07.1134.a029 through relay 10.1.0.253.
DHCPD:assigned IP address 10.1.0.3 to client 0b07.1134.a029.

Configuring DHCP Static Mapping

The DHCP—Static Mapping feature enables assignment of static IP addresses without creating numerous host pools with manual bindings by using a customer-created text file that the DHCP server reads. The benefit of this feature is that it eliminates the need for a long configuration file and reduces the space required in NVRAM to maintain address pools.

DHCP Database

A DHCP database contains the mappings between a client IP address and hardware address, referred to as a binding. There are two types of bindings: manual bindings that map a single hardware address to a single IP address, and automatic bindings that dynamically map a hardware address to an IP address from a pool of IP addresses. Manual (also known as static) bindings can be configured individually directly on the router or, by using the DHCP—Static Mapping feature, these static bindings can be read from a separate static mapping text file. The static mapping text files are read when a router reloads or the DHCP service restarts. These files are read-only.

The read static bindings are treated just like the manual bindings, in that they are:

Retained across DHCPRELEASEs from the clients.

Not timed out.

Deleted only upon deletion of the pool.

Provided appropriate exclusions for the contained addresses, which are created at the time of the read.

Just like automatic bindings and manual bindings, the static bindings from the static mapping text file are also displayed by using the show ip dhcp binding command.

This section contains the following tasks:

Creating the Static Mapping Text File (required)

Configuring the DHCP Server to Read a Static Mapping Text File (required)

Creating the Static Mapping Text File

Perform this task to create the static mapping text file. You will input your addresses in the text file, which is stored in the DHCP database for the DHCP server to read. There is no limit on the number of addresses in the file. The file format has the following elements:

Time the file was created

Database version number

IP address

Hardware type

Hardware address

Lease expiration

End-of-file designator

See Table 1 for more details about the format of the text file.

The following is a sample static mapping text file:

*time* Jan 21 2005 03:52 PM
!IP address    Type    Hardware address     Lease expiration
10.0.0.4 /24   1       0090.bff6.081e       Infinite
10.0.0.5 /28   id      00b7.0813.88f1.66    Infinite
10.0.0.2 /21   1       0090.bff6.081d       Infinite

Field

Description

*time*

Specifies the time the file was created. This field allows DHCP to differentiate between newer and older database versions when multiple agents are configured. The valid format of the time is Mmm dd yyyy hh:mm AM/PM.

*version* 2

Database version number.

IP address

Static IP address. If the subnet mask is not specified, a natural mask is assumed depending on the IP address. There must be a space between the IP address and mask.

Type

Specifies the hardware type. For example, type "1" indicates Ethernet. The type "id" indicates that the field is a DHCP client identifier. Legal values can be found online at http://www.iana.org/assignments/arp-parameters in the "Number Hardware Type" list.

Hardware address

Specifies the hardware address.

When the type is numeric, it refers to the hardware media. Legal values can be found online at http://www.iana.org/assignments/arp-parameters in the "Number Hardware Type" list.

When the type is "id," this means that we are matching on the client identifier.

For more information about the client identifier, please see RFC 2132, DHCP Options and BOOTP Vendor Extensions, section 9.14, located at http://www.ietf.org/rfc/rfc2132.txt.

or the client-identifier command reference page located at http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcr/tiad_r/adr_a1ht.htm#wp1125872.

If you are unsure what client identifier to match on, use the debug dhcp detail command to display the client identifier being sent to the DHCP server from the client.

Lease expiration

Specifies the expiration of the lease. "Infinite" specifies that the duration of the lease is unlimited.

*end*

End of file. DHCP uses the *end* designator to detect file truncation.


Configuring the DHCP Server to Read a Static Mapping Text File

Perform this task to configure the DHCP server to read the static mapping text file.

Prerequisites

The administrator should create the static mapping text file in the correct format and configure the address pools before performing this task.

Before editing the file, you must disable the DHCP server using the no service dhcp command.

Restrictions

The static bindings must not be deleted when a DHCPRELEASE is received or must not be timed out by the DHCP timer. The static bindings should be treated just like manual bindings created by using the ip dhcp pool command.

SUMMARY STEPS

1. enable

2. configureterminal

3. ip dhcp pool name

4. origin fileurl

5. end

6. show ip dhcp binding[address]

DETAILED STEPS

 

Command or Action

Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

ip dhcp pool name

Example:

Router(config)# ip dhcp pool pool1

Assigns a name to a DHCP pool and enters DHCP configuration mode.

Note If you have already configured the IP DHCP pool name using the ip dhcp pool command and the static file URL using the origin file command, you must perform a fresh read using the no service dhcp command and service dhcp command.

Step 4 

origin fileurl

Example:

Router(dhcp-config)# origin file tftp://10.1.0.1/static-bindings

Specifies the URL from which the DHCP server can locate the text file.

Step 5 

end

Example:

Router(dhcp-config)# end

Returns to privileged EXEC mode.

Step 6 

show ip dhcp binding [address]

Example:

Router# show ip dhcp binding

(Optional) Displays a list of all bindings created on a specific DHCP server.

Examples

The following example shows the address bindings that have been configured:

Router# show ip dhcp binding
00:05:14:%SYS-5-CONFIG_I: Configured from console by console
Bindings from all pools not associated with VRF:
IP address  Client-ID/            Ls expir   Type    Hw address           User name
10.9.9.4/8  0063.7363.2d30.3036.  Infinite   Static  302e.3762.2e39.3634. 632d.4574.8892.
10.9.9.1/24 0063.6973.636f.2d30.  Infinite   Static  3036.302e.3437.3165. 2e64.6462.342d.

The following sample shows each entry in the static mapping text file:

*time* Jan 21 2005 22:52 PM
!IP address Type        Hardware address                              Lease expiration
10.19.9.1 /24    id          0063.6973.636f.2d30.3036.302e.3437
10.9.9.4         id          0063.7363.2d30.3036.302e.3762.2e39.3634.632d  Infinite

The following sample debug output shows the reading of the static mapping text file from the TFTP server:

Router# debug ip dhcp server
Loading abc/static_pool from 10.19.192.33 (via Ethernet0):
*May 26 23:14:21.259: DHCPD: contacting agent tftp://10.19.192.33/abc/static_pool (attempt 0)

 

Pools

Introduction to pools

In a typical client-server scenario, a client request goes to the destination IP address specified in the header of the request. For sites with a large amount of incoming traffic, the destination server can quickly become overloaded as it tries to service a large number of requests. To solve this problem, BIG-IP®Local Traffic ManagerTM distributes client requests to multiple servers instead of to the specified destination IP address only. You configure Local Traffic Manager to do this when you create a load balancing pool.

What is a load balancing pool?

A load balancing pool is a logical set of devices, such as web servers, that you group together to receive and process traffic. Instead of sending client traffic to the destination IP address specified in the client request, Local Traffic Manager sends the request to any of the servers that are members of that pool. This helps to efficiently distribute the load on your server resources.

When you create a pool, you assign pool members to the pool. A pool member is a logical object that represents a physical node (server), on the network. You then associate the pool with a virtual server on the BIG-IP system. Once you have assigned a pool to a virtual server, Local Traffic Manager directs traffic coming into the virtual server to a member of that pool. An individual pool member can belong to one or multiple pools, depending on how you want to manage your network traffic.

The specific pool member to which Local Traffic Manager chooses to send the request is determined by the load balancing method that you have assigned to that pool. A load balancing method is an algorithm that Local Traffic Manager uses to select a pool member for processing a request. For example, the default load balancing method is Round Robin, which causes Local Traffic Manager to send each incoming request to the next available member of the pool, thereby distributing requests evenly across the servers in the pool.

To configure and manage pools, log in to the BIG-IP Configuration utility, and on the Main tab, expand Local Traffic, and click Pools.

Pool features

You can configure Local Traffic Manager to perform a number of different operations for a pool. For example, you can:

You use the Configuration utility to create a load balancing pool, or to modify a pool and its members. When you create a pool, LTM® automatically assigns a group of default settings to that pool and its members. You can retain these default settings or modify them. Also, you can modify the settings at a later time, after you have created the pool.

Pool settings

Table 4.1 lists the settings that you can configure for a pool. Following this table is a more detailed description of each setting.

Health monitor association

Health monitors are a key feature of Local Traffic Manager. Health monitors help to ensure that a server is in an up state and able to receive traffic. When you want to associate a monitor with an entire pool of servers, you do not need to explicitly associate that monitor with each individual server. Instead, you can simply assign the monitor to the pool itself. Local Traffic Manager then automatically monitors each member of the pool.

Local Traffic Manager contains many different pre-configured monitors that you can associate with pools, depending on the type of traffic you want to monitor. You can also create your own custom monitors and associate them with pools. The only monitor types that are not available for associating with pools are monitors that are specifically designed to monitor nodes and not pools or pool members. That is, the destination address in the monitor specifies an IP address only, rather than an IP address and a service port. These monitor types are:

With Local Traffic Manager, you can configure your monitor associations in many useful ways:

When a server that is designated as a pool member allows multiple processes to exist on the same IP address and port, you can check the health or status of each process. To do this, you can add the server to multiple pools, and then within each pool, associate a monitor with the that server. The monitor you associate with each server checks the health of the process running on that server.

When associating a monitor with an entire pool, you can exclude an individual pool member from being associated with that monitor. In this case, you can associate a different monitor for that particular pool member, or you can exclude that pool member from health monitoring altogether. For example, you can associate pool members A, B, and D with the http monitor, while you associate pool member C with the https monitor.

Pool member availability

You can specify a minimum number of health monitors. Before Local Traffic Manager can report the pool member as being in an up state, this number of monitors, at a minimum, must report a pool member as being available to receive traffic.

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