DHCP Commands

Use the commands in this chapter to configure and monitor Dynamic Host Configuration Protocol (DHCP). For DHCP configuration information and examples, refer to the "Configuring DHCP" chapter of the Cisco IOS IP and IP Routing Configuration Guide.

bootfile

To specify the name of the default boot image for a Dynamic Host Configuration Protocol (DHCP) client, use the bootfile DHCP pool configuration command. To delete the boot image name, use the no form of this command.

bootfile filename

no bootfile

Syntax Description

filename

Specifies the name of the file that is used as a boot image.

filename	Specifies the name of the file that is used as a boot image.

Defaults

No default behavior or values.

Command Modes

DHCP pool configuration

Command History

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12.0(1)T

This command was introduced.

Release	Modification
12.0(1)T	This command was introduced.

Examples

The following example specifies xllboot as the name of the boot file:

bootfile xllboot

Related Commands

Command Description

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

next-server

Configures the next server in a DHCP client's boot process.

Command	Description
ip dhcp pool	Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.
next-server	Configures the next server in a DHCP client's boot process.

clear ip dhcp binding

To delete an automatic address binding from the Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server database, use the clear ip dhcp binding privileged EXEC command.

clear ip dhcp binding {address | * }

Syntax Description

address

The address of the binding you want to clear.

*

Clears all automatic bindings.

address	The address of the binding you want to clear.
*	Clears all automatic bindings.

Command Modes

Privileged EXEC

Command History

Release Modification

12.0(1)T

This command was introduced.

Release	Modification
12.0(1)T	This command was introduced.

Usage Guidelines

Typically, the address denotes the client's IP address. If the asterisk (*) character is used as the address parameter, DHCP clears all automatic bindings.

Use the no ip dhcp pool global configuration command to delete a manual binding.

Examples

The following example deletes the address binding 10.12.1.99 from a DHCP server database:

clear ip dhcp binding 10.12.1.99

Related Commands

Command Description

show ip dhcp binding

Displays address bindings on the Cisco IOS DHCP Server.

Command	Description
show ip dhcp binding	Displays address bindings on the Cisco IOS DHCP Server.

clear ip dhcp conflict

To clear an address conflict from the Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server database, use the clear ip dhcp conflict privileged EXEC command.

clear ip dhcp conflict {address | *}

Syntax Description

address

The IP address of the host that contains the conflicting address you want to clear.

*

Clears all address conflicts.

address	The IP address of the host that contains the conflicting address you want to clear.
*	Clears all address conflicts.

Command Modes

Privileged EXEC

Command History

Release Modification

12.0(1)T

This command was introduced.

Release	Modification
12.0(1)T	This command was introduced.

Usage Guidelines

The server detects conflicts using a ping session. The client detects conflicts using gratuitous Address Resolution Protocol (ARP). If the asterisk (*) character is used as the address parameter, DHCP clears all conflicts.

Examples

The following example shows an address conflict of 10.12.1.99 being deleted from the DHCP server database:

clear ip dhcp conflict 10.12.1.99

Related Commands

Command Description

show ip dhcp conflict

Displays address conflicts found by a Cisco IOS DHCP Server when addresses are offered to the client.

Command	Description
show ip dhcp conflict	Displays address conflicts found by a Cisco IOS DHCP Server when addresses are offered to the client.

clear ip dhcp server statistics

To reset all Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server counters, use the clear ip dhcp server statistics privileged EXEC command.

clear ip dhcp server statistics

Syntax Description

This command has no arguments or keywords.

Command Modes

Privileged EXEC

Command History

Release Modification

12.0(1)T

This command was introduced.

Release	Modification
12.0(1)T	This command was introduced.

Usage Guidelines

The show ip dhcp server statistics command displays DHCP counters. All counters are cumulative. The counters will be initialized, or set to zero, with this command.

Examples

The following example resets all DHCP counters to zero:

clear ip dhcp server statistics

Related Commands

Command Description

show ip dhcp server statistics

Displays Cisco IOS DHCP Server statistics.

Command	Description
show ip dhcp server statistics	Displays Cisco IOS DHCP Server statistics.

client-identifier

To specify the unique identifier (in dotted-hexadecimal notation) for a Microsoft Dynamic Host Configuration Protocol (DHCP) client, use the client-identifier DHCP pool configuration command. It is valid for manual bindings only. To delete the client identifier, use the no form of this command.

client-identifier unique-identifier

no client-identifier

Syntax Description

unique-identifier

The distinct identification of the client in dotted-hexadecimal notation, for example, 01b7.0813.8811.66.

unique-identifier	The distinct identification of the client in dotted-hexadecimal notation, for example, 01b7.0813.8811.66.

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Release	Modification
12.0(1)T	This command was introduced.

Usage Guidelines

Microsoft DHCP clients require client identifiers instead of hardware addresses. The client identifier is formed by concatenating the media type and the MAC address. For example, the Microsoft client identifier for Ethernet address b708.1388.f166 is 01b7.0813.88f1.66, where 01 represents the Ethernet media type. For a list of media type codes, refer to the "Address Resolution Protocol Parameters" section of RFC 1700, Assigned Numbers.

Examples

The following example specifies the client identifier for Mac address b7.0813.8811.66 in dotted-hexadecimal notation:

client-identifier 01b7.0813.8811.66

Related Commands

Command Description

hardware-address

Specifies the hardware address of a DHCP client.

host

Specifies the IP address and network mask for a manual binding to a DHCP client.

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

Command	Description
hardware-address	Specifies the hardware address of a DHCP client.
host	Specifies the IP address and network mask for a manual binding to a DHCP client.
ip dhcp pool	Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

client-name

To specify the name of a Dynamic Host Configuration Protocol (DHCP) client, use the client-name DHCP pool configuration command. The client name should not include the domain name. To remove the client name, use the no form of this command.

client-name name

no client-name

Syntax Description

name

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.

name	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.

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Release	Modification
12.0(1)T	This command was introduced.

Examples

The following example specifies a string client1 that will be the name of the client:

client-name client1

Related Commands

Command Description

host

Specifies the IP address and network mask for a manual binding to a DHCP client.

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

Command	Description
host	Specifies the IP address and network mask for a manual binding to a DHCP client.
ip dhcp pool	Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

default-router

To specify the default router list for a Dynamic Host Configuration Protocol (DHCP) client, use the default-router DHCP pool configuration command. To remove the default router list, use the no form of this command.

default-router address [address2...address8]

no default-router

Syntax Description

address

Specifies the IP address of a router. One IP address is required, although you can specify up to eight addresses in one command line.

address2...address8

(Optional) Specifies up to eight addresses in the command line.

address	Specifies the IP address of a router. One IP address is required, although you can specify up to eight addresses in one command line.
address2...address8	(Optional) Specifies up to eight addresses in the command line.

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Release	Modification
12.0(1)T	This command was introduced.

Usage Guidelines

The IP address of the router should be on the same subnet as the client subnet. You can specify up to eight routers in the list. Routers are listed in order of preference (address1 is the most preferred router, address2 is the next most preferred router, and so on).

Examples

The following example specifies 10.12.1.99 as the IP address of the default router:

default-router 10.12.1.99

Related Commands

Command Description

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

Command	Description
ip dhcp pool	Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

dns-server

To specify the Domain Name System (DNS) IP servers available to a Dynamic Host Configuration Protocol (DHCP) client, use the dns-server DHCP pool configuration command. To remove the DNS server list, use the no form of this command.

dns-server address [address2...address8]

no dns-server

Syntax Description

address

Specifies the IP address of a DNS server. One IP address is required, although you can specify up to eight addresses in one command line.

address2...address8

(Optional) Specifies up to eight addresses in the command line.

address	Specifies the IP address of a DNS server. One IP address is required, although you can specify up to eight addresses in one command line.
address2...address8	(Optional) Specifies up to eight addresses in the command line.

Defaults

If DNS IP servers are not configured for a DHCP client, the client cannot correlate host names to IP addresses.

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Release	Modification
12.0(1)T	This command was introduced.

Usage Guidelines

Servers are listed in order of preference (address1 is the most preferred server, address2 is the next most preferred server, and so on).

Examples

The following example specifies 10.12.1.99 as the IP address of the domain name server of the client:

dns-server 10.12.1.99

Related Commands

Command Description

domain-name

Specifies the domain name for a DHCP client.

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

Command	Description
domain-name	Specifies the domain name for a DHCP client.
ip dhcp pool	Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

domain-name

To specify the domain name for a Dynamic Host Configuration Protocol (DHCP) client, use the domain-name DHCP pool configuration command. To remove the domain name, use the no form of this command.

domain-name domain

no domain-name

Syntax Description

domain

Specifies the domain name string of the client.

domain	Specifies the domain name string of the client.

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Release	Modification
12.0(1)T	This command was introduced.

Examples

The following example specifies cisco.com as the domain name of the client:

domain-name cisco.com

Related Commands

Command Description

dns-server

Specifies the DNS IP servers available to a DHCP client.

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

hardware-address

To specify the hardware address of a Dynamic Host Configuration Protocol (DHCP) client, use the hardware-address DHCP pool configuration command. It is valid for manual bindings only. To remove the hardware address, use the no form of this command.

hardware-address hardware-address type

no hardware-address

Syntax Description

hardware-address

Specifies the MAC address of the client's hardware platform.

type

Indicates the protocol of the hardware platform. Strings and values are acceptable. The string options are:

ethernet

ieee802

The value options are:

1 10Mb Ethernet

6 IEEE 802

If no type is specified, the default protocol is Ethernet.

Defaults

Ethernet is the default type if none is specified.

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Examples

The following example specifies b708.1388.f166 as the MAC address of the client:

hardware-address b708.1388.f166

Related Commands

Command Description

client-identifier

Specifies a Microsoft DHCP client's unique identifier (in dotted-hexadecimal notation).

host

Specifies the IP address and network mask for a manual binding to a DHCP client.

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

host

To specify the IP address and network mask for a manual binding to a Dynamic Host Configuration Protocol (DHCP) client, use the host DHCP pool configuration command. To remove the IP address of the client, use the no form of this command.

host address [mask | prefix-length]

no host

Syntax Description

address

Specifies the IP address of the client.

mask

(Optional) Specifies the network mask of the client.

prefix-length

(Optional) Specifies the number of bits that comprise the address prefix. The prefix is an alternative way of specifying the network mask of the client. The prefix length must be preceded by a forward slash (/).

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

If the mask and prefix length are unspecified, DHCP examines its address pools. If no mask is found in the pool database, the Class A, B, or C natural mask is used. This command is valid for manual bindings only.

Examples

The following example specifies 10.12.1.99 as the client's IP address and 255.255.248.0 as the subnet mask:

host 10.12.1.99 255.255.248.0

Related Commands

Command Description

client-identifier

Specifies a Microsoft DHCP client's unique identifier (in dotted-hexadecimal notation).

hardware-address

Specifies the hardware address of a DHCP client.

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places you in DHCP pool configuration mode.

network (DHCP)

Configures the subnet number and mask for a DHCP address pool on a Cisco IOS DHCP Server.

ip dhcp conflict logging

To enable conflict logging on a Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server, use the ip dhcp conflict logging global configuration command. To disable conflict logging, use the no form of this command.

ip dhcp conflict logging

no ip dhcp conflict logging

Syntax Description

This command has no arguments or keywords.

Defaults

Conflict logging is enabled.

Command Modes

Global configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

Cisco recommends using a DHCP server database agent to store automatic bindings. If you decide not to use a DHCP server database agent to store automatic bindings, use the no ip dhcp conflict logging command to disable the recording of address conflicts. By default, the Cisco IOS DHCP server records DHCP address conflicts in a log file.

Examples

The following example disables the recording of DHCP address conflicts:

no ip dhcp conflict logging

Related Commands

Command Description

clear ip dhcp conflict

Clears an address conflict from the Cisco IOS DHCP Server database.

ip dhcp database

Configures a Cisco IOS DHCP Server to save automatic bindings on a remote host called a database agent.

show ip dhcp conflict

Displays address conflicts found by a Cisco IOS DHCP Server when addresses are offered to the client.

ip dhcp database

You can configure a Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server to save automatic bindings on a remote host called a database agent. To configure a DHCP server database agent and database agent parameters, use the ip dhcp database global configuration command. To remove the database agent, use the no form of this command.

ip dhcp database url [timeout seconds | write-delay seconds]

no ip dhcp database url

Syntax Description

url

Specifies the remote file used to store the automatic bindings. Following are the acceptable URL file formats:

tftp://host/filename

ftp://user:password@host/filename

rcp://user@host/filename

timeout seconds

(Optional) Specifies how long, in seconds, the DHCP server should wait before aborting a database transfer. Transfers that exceed the timeout period are aborted. By default, DHCP waits 300 seconds before aborting a database transfer. Infinity is defined as 0 seconds.

write-delay seconds

(Optional) Specifies how soon the DHCP server should send database updates. By default, DHCP waits 300 seconds (5 minutes) before sending database changes. The minimum delay is 60 seconds.

Defaults

DHCP waits 300 seconds for both a write delay and a timeout.

Command Modes

Global configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

The administrator may configure multiple database agents. Bindings are transferred by using the File Transfer Protocol (FTP), Trivial File Transport Protocol (TFTP), or remote copy protocol (RCP).

Examples

The following example specifies the DHCP database transfer timeout value at 80 seconds:

ip dhcp database ftp://user:password@172.16.1.1/router-dhcp timeout 80

The following example specifies the DHCP database update delay value at 100 seconds:

ip dhcp database tftp://172.16.1.1/router-dhcp write-delay 100

Related Commands

Command Description

show ip dhcp database

Displays Cisco IOS DHCP Server database agent information.

ip dhcp excluded-address

To specify IP addresses that a Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server should not assign to DHCP clients, use the ip dhcp excluded-address global configuration command. To remove the excluded IP addresses, use the no form of this command.

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

no ip dhcp excluded-address low-address [high-address]

Syntax Description

low-address

The excluded IP address, or first IP address in an excluded address range.

high-address

(Optional) The last IP address in the excluded address range.

Defaults

All IP pool addresses are assignable.

Command Modes

Global configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

The DHCP server assumes that all pool addresses may be assigned to clients. Use this command to exclude a single IP address or a range of IP addresses.

Examples

The following example configures an excluded IP address range from 172.16.1.100 through 172.16.1.199:

ip dhcp excluded-address 172.16.1.100 172.16.1.199

Related Commands

Command Description

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

network (DHCP)

Configures the subnet number and mask for a DHCP address pool on a Cisco IOS DHCP Server.

ip dhcp ping packets

To specify the number of packets a Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server sends to a pool address as part of a ping operation, use the ip dhcp ping packets global configuration command. To prevent the server from pinging pool addresses, use the no form of this command.

ip dhcp ping packets count

no ip dhcp ping packets

Syntax Description

count

Indicates the number of ping packets that are sent before assigning the address to a requesting client. The default value is two packets.

Defaults

Two packets

Command Modes

Global configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

The DHCP server pings a pool address before assigning the address to a requesting client. If the ping is unanswered, the DHCP server assumes (with a high probability) that the address is not in use and assigns the address to the requesting client.

Examples

The following example specifies five ping attempts by the DHCP server before ceasing any further ping attempts:

ip dhcp ping packets 5

Related Commands

Command Description

clear ip dhcp conflict

Clears an address conflict from the Cisco IOS DHCP Server database.

ip dhcp ping timeout

Specifies how long a Cisco IOS DHCP Server waits for a ping reply from an address pool.

show ip dhcp conflict

Displays address conflicts found by a Cisco IOS DHCP Server when addresses are offered to the client.

ip dhcp ping timeout

To specify how long a Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server waits for a ping reply from an address pool, use the ip dhcp ping timeout global configuration command. To restore the default number of milliseconds (500) of the timeout, use the no form of this command.

ip dhcp ping timeout milliseconds

no ip dhcp ping timeout

Syntax Description

milliseconds

The amount of time in milliseconds that the DHCP server waits for a ping reply before it stops attempting to reach a pool address for client assignment. The maximum timeout is 10000 milliseconds (10 seconds). The default timeout is 500 milliseconds.

Defaults

500 milliseconds

Command Modes

Global configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

This command specifies how long to wait for a ping reply in milliseconds.

Examples

The following example specifies that the DHCP server will wait 800 milliseconds for a ping reply before considering the ping a failure:

ip dhcp ping timeout 800

Related Commands

Command Description

clear ip dhcp conflict

Clears an address conflict from the Cisco IOS DHCP Server database.

ip dhcp ping packets

Specifies the number of packets a Cisco IOS DHCP Server sends to a pool address as part of a ping operation.

show ip dhcp conflict

Displays address conflicts found by a Cisco IOS DHCP Server when addresses are offered to the client.

ip dhcp pool

To configure a Dynamic Host Configuration Protocol (DHCP) address pool on a Cisco IOS DHCP Server and enter DHCP pool configuration mode, use the ip dhcp pool global configuration command. To remove the address pool, use the no form of this command.

ip dhcp pool name

no ip dhcp pool name

Syntax Description

name

Can either be a symbolic string (such as "engineering") or an integer (such as 0).

Defaults

DHCP address pools are not configured.

Command Modes

Global configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

During execution, the configuration mode changes to DHCP pool configuration mode, identified by the (config-dhcp)# prompt. In this mode, the administrator can configure pool parameters, like the IP subnet number and default router list.

Examples

The following example configures pool1 as the DHCP address pool:

ip dhcp pool pool1

Related Commands

Command Description

host

Specifies the IP address and network mask for a manual binding to a DHCP client.

ip dhcp excluded-address

Specifies IP addresses that a Cisco IOS DHCP Server should not assign to DHCP clients.

network (DHCP)

Configures the subnet number and mask for a DHCP address pool on a Cisco IOS DHCP Server.

ip dhcp relay information check

To configure a Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server to validate the relay agent information option in forwarded BOOTREPLY messages, use the ip dhcp relay information check global configuration command. To disable an information check, use the no form of this command.

ip dhcp relay information check

no ip dhcp relay information check

Syntax Description

This command has no arguments or keywords.

Defaults

The DHCP server checks relay information. Invalid messages are dropped.

Command Modes

Global configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

This command is used by cable modem termination systems. By default, DHCP checks relay information. Invalid messages are dropped.

Examples

The following example configures the DHCP server to check that the relay agent information option in forwarded BOOTREPLY messages is valid:

ip dhcp relay information check

Related Commands

Command Description

ip dhcp relay information option

Configures a Cisco IOS DHCP Server to insert the DHCP relay agent information option in forwarded BOOTREQUEST messages.

ip dhcp relay information policy

Configures a DHCP relay agent's information reforwarding policy (what a DHCP relay agent should do if a message already contains relay information).

ip dhcp relay information option

To configure a Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server to insert the DHCP relay agent information option in forwarded BOOTREQUEST messages, use the ip dhcp relay information option global configuration command. To disable inserting relay information into forwarded BOOTREQUEST messages, use the no form of this command.

ip dhcp relay information option

no ip dhcp relay information option

Syntax Description

This command has no arguments or keywords.

Defaults

The DHCP server does not insert relay information.

Command Modes

Global configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

This command is used by cable modem termination systems. By default, DHCP does not insert relay information.

Examples

The following example configures a DHCP server to insert the DHCP relay agent information option in forwarded BOOTREQUEST messages:

ip dhcp relay information option

Related Commands

Command Description

ip dhcp relay information check

Configures a Cisco IOS DHCP Server to validate the relay agent information option in forwarded BOOTREPLY messages.

ip dhcp relay information policy

Configures a DHCP relay agent's information reforwarding policy (what a DHCP relay agent should do if a message already contains relay information).

ip dhcp relay information policy

To configure the information reforwarding policy for a Dynamic Host Configuration Protocol (DHCP) relay agent (what a relay agent should do if a message already contains relay information), use the ip dhcp relay information policy global configuration command. To restore the default relay information policy, use the no form of this command .

ip dhcp relay information policy {drop | keep | replace}

no ip dhcp relay information policy

Syntax Description

drop

Directs the DHCP relay agent to discard messages with existing relay information if the relay information option is already present.

keep

Indicates that existing information is left unchanged on the DHCP relay agent.

replace

Indicates that existing information is overwritten on the DHCP relay agent.

Defaults

The DHCP server replaces existing relay information.

Command Modes

Global configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

This command is used by cable modem termination systems. When a DHCP relay agent receives a message from a another DHCP relay agent, relay information might already be present in the message. By default, the relay information from the previous relay agent is replaced.

Examples

The following examples configure a DHCP relay agent to drop messages with existing relay information, keep existing information, and replace existing information:

ip dhcp relay information policy drop
 
ip dhcp relay information policy keep
 
ip dhcp relay information policy replace

Related Commands

Command Description

ip dhcp relay information check

Configures a Cisco IOS DHCP Server to validate the relay agent information option in forwarded BOOTREPLY messages.

ip dhcp relay information option

Configures a Cisco IOS DHCP Server to insert the DHCP relay agent information option in forwarded BOOTREQUEST messages.

lease

To configure the duration of the lease for an IP address that is assigned from a Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server to a DHCP client, use the lease DHCP pool configuration command. To restore the default value, use the no form of this command.

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

no lease

Syntax Description

days

Specifies the duration of the lease in numbers of days.

hours

(Optional) Specifies the number of hours in the lease. A days value must be supplied before you can configure an hours value.

minutes

(Optional) Specifies the number of minutes in the lease. A days value and an hours value must be supplied before you can configure a minutes value.

infinite

Specifies the duration of the lease is unlimited.

Defaults

One day

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Examples

The following example shows a one-day lease:

lease 1

The following example shows a one-hour lease:

lease 0 1

The following example shows a one-minute lease:

lease 0 0 1

The following example shows an infinite (unlimited) lease:

lease infinite

Related Commands

Command Description

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places you in DHCP pool configuration mode.

netbios-name-server

To configure NetBIOS Windows Internet Naming Service (WINS) name servers that are available to Microsoft Dynamic Host Configuration Protocol (DHCP) clients, use the netbios-name-server DHCP pool configuration command. To remove the NetBIOS name server list, use the no form of this command.

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

no netbios-name-server

Syntax Description

address

Specifies the IP address of the NetBIOS WINS name server. One IP address is required, although you can specify up to eight addresses in one command line.

address2...address8

(Optional) Specifies up to eight addresses in the command line.

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

One IP address is required, although you can specify up to eight addresses in one command line. Servers are listed in order of preference (address1 is the most preferred server, address2 is the next most preferred server, and so on).

Examples

The following example specifies the IP address of a NetBIOS name server available to the client:

netbios-name-server 10.12.1.90

Related Commands

Command Description

dns-server

Specifies the DNS IP servers available to a DHCP client.

domain-name

Specifies the domain name for a DHCP client.

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places you in DHCP pool configuration mode.

netbios-node-type

Configures the NetBIOS node type for Microsoft DHCP clients.

netbios-node-type

To configure the NetBIOS node type for Microsoft Dynamic Host Configuration Protocol (DHCP) clients, use the netbios-node-type DHCP pool configuration command. To remove the NetBIOS node type, use the no form of this command.

netbios-node-type type

no netbios-node-type

Syntax Description

type

Specifies the NetBIOS node type. Valid types are:

b-node Broadcast

p-node Peer-to-peer

m-node Mixed

h-node Hybrid (recommended)

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

The recommended type is h-node (hybrid).

Examples

The following example specifies the client's NetBIOS type as hybrid:

netbios node-type h-node

Related Commands

Command Description

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places you in DHCP pool configuration mode.

netbios-name-server

Configures NetBIOS WINS name servers that are available to Microsoft DHCP clients.

network (DHCP)

To configure the subnet number and mask for a Dynamic Host Configuration Protocol (DHCP) address pool on a Cisco IOS DHCP Server, use the network DHCP pool configuration command. To remove the subnet number and mask, use the no form of this command.

network network-number [mask | prefix-length]

no network

Syntax Description

network-number

The IP address of the DHCP address pool.

mask

(Optional) The bit combination that renders which portion of the address of the DHCP address pool refers to the network or subnet and which part refers to the host.

prefix-length

(Optional) Specifies the number of bits that comprise the address prefix. The prefix is an alternative way of specifying the network mask of the client. The prefix length must be proceeded by a forward slash (/).

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

This command is valid for DHCP subnetwork address pools only. If the mask or prefix length is not specified, the class A, B, or C natural mask is used. The DHCP server assumes that all host addresses are available. The system administrator can exclude subsets of the address space by using the ip dhcp excluded-address command.

Examples

The following example configures 172.16.0.0/16 as the DHCP pool's subnetwork number and mask:

network 172.16.0.0 /16

Related Commands

Command Description

host

Specifies the IP address and network mask for a manual binding to a DHCP client.

ip dhcp excluded-address

Specifies IP addresses that a Cisco IOS DHCP Server should not assign to DHCP clients.

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places you in DHCP pool configuration mode.

next-server

To configure the next server in the boot process of a Dynamic Host Configuration Protocol (DHCP) client, use the next-server DHCP pool configuration command. To remove the boot server list, use the no form of this command.

next-server address [address2...address8]

no next-server address

Syntax Description

address

Specifies the IP address of the next server in the boot process, which is typically a Trivial File Transfer Protocol (TFTP) server. One IP address is required, although you can specify up to eight addresses in one command line.

address2...address8

(Optional) Specifies up to eight addresses in the command line.

Defaults

If the next-server command is not used to configure a boot server list, the DHCP server uses inbound interface helper addresses as boot servers.

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

You can specify up to eight servers in the list. Servers are listed in order of preference (address1 is the most preferred server, address2 is the next most preferred server, and so on).

Examples

The following example specifies 10.12.1.99 as the IP address of the next server in the boot process:

next-server 10.12.1.99

Related Commands

Command Description

bootfile

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

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places you in DHCP pool configuration mode.

ip helper-address

Forwards UDP broadcasts, including BOOTP, received on an interface.

option

Configures Cisco IOS DHCP Server options.

option

To configure Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server options, use the option DHCP pool configuration command. To remove the options, use the no form of this command.

option code [instance number] {ascii string | hex string | ip address}

no option code [instance number]

Syntax Description

code

Specifies the DHCP option code.

instance number

(Optional) Specifies a number from 0 to 255.

ascii string

Specifies an NVT ASCII character string. ASCII character strings that contain white space must be deliminated by quotation marks.

hex string

Specifies dotted-hexadecimal data. Each byte in hexidecimal character strings is two hexidecimal digits---each byte can be separated by a period, colon, or white space.

ip address

Specifies an IP address.

Defaults

The default instance number is 0.

Command Modes

DHCP pool configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

DHCP provides a framework for passing configuration information to hosts on a TCP/IP network. Configuration parameters and other control information are carried in tagged data items that are stored in the options field of the DHCP message. The data items themselves are also called options. The current set of DHCP options are documented in RFC 2131, Dynamic Host Configuration Protocol.

Examples

The following example configures DHCP option 19, which specifies whether the client should configure its IP layer for packet forwarding. A value of 0 means disable IP forwarding; a value of 1 means enable IP forwarding. IP forwarding is enabled in the following example:

option 19 hex 01

The following example configures DHCP option 72, which specifies the World Wide Web servers for DHCP clients. World Wide Web servers 172.16.3.252 and 172.16.3.253 are configured in the following example:

option 72 ip 172.16.3.252 172.16.3.253

Related Commands

Command Description

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP Server and places you in DHCP pool configuration mode.

service dhcp

To enable the Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server feature on your router, use the service dhcp global configuration command. To disable the Cisco IOS DHCP Server feature, use the no form of this command.

service dhcp

no service dhcp

Syntax Description

This command has no arguments or keywords.

Defaults

Enabled

Command Modes

Global configuration

Command History

Release Modification

12.0(1)T

This command was introduced.

Examples

The following example enables DHCP services on the DHCP server:

service dhcp

show ip dhcp binding

To display address bindings on the Cisco IOS Dynamic Host Configuration Protocol (DHCP) server, use the show ip dhcp binding EXEC command.

show ip dhcp binding [address]

Syntax Description

address

(Optional) Specifies the IP address of the DHCP client for which bindings will be displayed.

Command Modes

EXEC

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

If the address is not specified, all address bindings are shown. Otherwise, only the binding for the specified client is displayed.

Examples

The following examples show the DHCP binding address parameters, including an IP address, an associated MAC address, a lease expiration date, and the type of address assignment that have occurred. Table 11 lists descriptions of the fields in each example.

Router> show ip dhcp binding 172.16.1.11
 
IP address    Hardware address    Lease expiration        Type
172.16.1.11   00a0.9802.32de      Feb 01 1998 12:00 AM    Automatic
 
Router> show ip dhcp binding 172.16.3.254
 
IP address    Hardware address    Lease expiration        Type
172.16.2.254  02c7.f800.0422      Infinite                Manual

Table 11: show ip dhcp binding Field Descriptions

Field Description

IP address

The IP address of the host as recorded on the DHCP server.

Hardware address

The MAC address or client identifier of the host as recorded on the DHCP server.

Lease expiration

The lease expiration date of the IP address of the host.

Type

The manner in which the IP address was assigned to the host.

Related Commands

Command Description

clear ip dhcp binding

Deletes an automatic address binding from the Cisco IOS DHCP Server database.

show ip dhcp conflict

To display address conflicts found by a Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server when addresses are offered to the client, use the show ip dhcp conflict EXEC command.

show ip dhcp conflict [address]

Syntax Description

address

(Optional) Specifies the IP address of the conflict found.

Command Modes

EXEC

Command History

Release Modification

12.0(1)T

This command was introduced.

Usage Guidelines

The server detects conflicts using ping. The client detects conflicts using gratuitous Address Resolution Protocol (ARP). If an address conflict is detected, the address is removed from the pool and the address will not be assigned until an administrator resolves the conflict.

Examples

The following example displays the detection method and detection time for all IP addresses the DHCP server has offered that have conflicts with other devices. Table 12 lists descriptions of the fields in the example.

Router> show ip dhcp conflict
 
IP address    Detection Method     Detection time
172.16.1.32   Ping                 Feb 16 1998 12:28 PM
172.16.1.64   Gratuitous ARP       Feb 23 1998 08:12 AM

Table 12: show ip dhcp conflict Field Descriptions

Field Description

IP Address

The IP address of the host as recorded on the DHCP server.

Detection Method

The manner in which the IP address of the hosts were found on the DHCP server. Can be a ping or a gratuitous ARP.

Detection time

The time when the conflict was found.

Related Commands

Command Description

clear ip dhcp conflict

Clears an address conflict from the Cisco IOS DHCP Server database.

ip dhcp ping packets

Specifies the number of packets a Cisco IOS DHCP Server sends to a pool address as part of a ping operation.

ip dhcp ping timeout

Specifies how long a Cisco IOS DHCP Server waits for a ping reply from an address pool.

show ip dhcp database

To display Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server database agent information, use the show ip dhcp database Privileged EXEC command.

show ip dhcp database [url]

Syntax Description

url

(Optional) Specifies the remote file used to store automatic DHCP bindings. Following are the acceptable URL file formats:

tftp://host/filename

ftp://user:password@host/filename

rcp://user@host/filename

Defaults

If a URL is not specified, all database agent records are shown. Otherwise, only information about the specified agent is displayed.

Command Modes

Privileged EXEC

Command History

Release Modification

12.0(1)T

This command was introduced.

Examples

The following example shows all DHCP server database agent information. Table 13 lists descriptions for each field in the example.

Router# show ip dhcp database
 
URL       :    ftp://user:password@172.16.4.253/router-dhcp
Read      :    Dec 01 1997 12:01 AM
Written   :    Never
Status    :    Last read succeeded. Bindings have been loaded in RAM.
Delay     :    300 seconds
Timeout   :    300 seconds
Failures  :    0
Successes :    1

Table 13: show ip dhcp database Field Descriptions

Field Description

URL

Specifies the remote file used to store automatic DHCP bindings. Following are the acceptable URL file formats:

tftp://host/filename

ftp://user:password@host/filename

rcp://user@host/filename

Read

The last time bindings were read from the file server.

Written

The last time bindings were written to the file server.

Status

Indication of whether the last read or write of host bindings was successful.

Delay

The amount of time to wait before updating the database.

Timeout

The amount of time before the file transfer is aborted.

Failures

The number of failed file transfers.

Successes

The number of successful file transfers.

Related Commands

Command Description

ip dhcp database

Configures a Cisco IOS DHCP Server to save automatic bindings on a remote host called a database agent.

show ip dhcp server statistics

To display Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server statistics, use the show ip dhcp server statistics EXEC command.

show ip dhcp server statistics

Syntax Description

This command has no arguments or keywords.

Command Modes

EXEC

Command History

Release Modification

12.0(1)T

This command was introduced.

Examples

The following example displays DHCP server statistics. Table 14 lists descriptions for each field in the example.

Router> show ip dhcp server statistics
 
Memory usage          40392
Address pools         3
Database agents       1
Automatic bindings    190
Manual bindings       1
Expired bindings      3
Malformed messages    0
 
Message               Received
BOOTREQUEST           12
DHCPDISCOVER          200
DHCPREQUEST           178
DHCPDECLINE           0
DHCPRELEASE           0
DHCPINFORM            0
 
Message               Sent
BOOTREPLY             12
DHCPOFFER             190
DHCPACK               172
DHCPNAK               6

Table 14: show ip dhcp server statistics Field Descriptions

Field Description

Memory usage

The number of bytes of RAM allocated by the DHCP server.

Address pools

The number of configured address pools in the DHCP database.

Database agents

The number of database agents configured in the DHCP database.

Automatic bindings

The number of IP addresses that have been automatically mapped to the MAC addresses of hosts that are found in the DHCP database.

Manual bindings

The number of IP addresses that have been manually mapped to the MAC addresses of hosts that are found in the DHCP database.

Expired bindings

The number of expired leases.

Malformed messages

The number of truncated or corrupted messages that were received by the DHCP server.

Message

The DHCP message type that was received by the DHCP server.

Received

The number of DHCP messages that were received by the DHCP server.

Sent

The number of DHCP messages that were sent by the DHCP server.

Related Commands

Command Description

clear ip dhcp server statistics

Resets all Cisco IOS DHCP Server counters.

Command	Description
dns-server	Specifies the DNS IP servers available to a DHCP client.
ip dhcp pool	Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

hardware-address	Specifies the MAC address of the client's hardware platform.
type	Indicates the protocol of the hardware platform. Strings and values are acceptable. The string options are: ethernet ieee802 The value options are: 1 10Mb Ethernet 6 IEEE 802 If no type is specified, the default protocol is Ethernet.

Command	Description
client-identifier	Specifies a Microsoft DHCP client's unique identifier (in dotted-hexadecimal notation).
host	Specifies the IP address and network mask for a manual binding to a DHCP client.
ip dhcp pool	Configures a DHCP address pool on a Cisco IOS DHCP Server and places the routing device in DHCP pool configuration mode.

address	Specifies the IP address of the client.
mask	(Optional) Specifies the network mask of the client.
prefix-length	(Optional) Specifies the number of bits that comprise the address prefix. The prefix is an alternative way of specifying the network mask of the client. The prefix length must be preceded by a forward slash (/).

Command	Description
clear ip dhcp conflict	Clears an address conflict from the Cisco IOS DHCP Server database.
ip dhcp database	Configures a Cisco IOS DHCP Server to save automatic bindings on a remote host called a database agent.
show ip dhcp conflict	Displays address conflicts found by a Cisco IOS DHCP Server when addresses are offered to the client.

url	Specifies the remote file used to store the automatic bindings. Following are the acceptable URL file formats: tftp://host/filename ftp://user:password@host/filename rcp://user@host/filename
timeout seconds	(Optional) Specifies how long, in seconds, the DHCP server should wait before aborting a database transfer. Transfers that exceed the timeout period are aborted. By default, DHCP waits 300 seconds before aborting a database transfer. Infinity is defined as 0 seconds.
write-delay seconds	(Optional) Specifies how soon the DHCP server should send database updates. By default, DHCP waits 300 seconds (5 minutes) before sending database changes. The minimum delay is 60 seconds.

low-address	The excluded IP address, or first IP address in an excluded address range.
high-address	(Optional) The last IP address in the excluded address range.

Command	Description
ip dhcp relay information option	Configures a Cisco IOS DHCP Server to insert the DHCP relay agent information option in forwarded BOOTREQUEST messages.
ip dhcp relay information policy	Configures a DHCP relay agent's information reforwarding policy (what a DHCP relay agent should do if a message already contains relay information).

Command	Description
ip dhcp relay information check	Configures a Cisco IOS DHCP Server to validate the relay agent information option in forwarded BOOTREPLY messages.
ip dhcp relay information policy	Configures a DHCP relay agent's information reforwarding policy (what a DHCP relay agent should do if a message already contains relay information).

drop	Directs the DHCP relay agent to discard messages with existing relay information if the relay information option is already present.
keep	Indicates that existing information is left unchanged on the DHCP relay agent.
replace	Indicates that existing information is overwritten on the DHCP relay agent.

days	Specifies the duration of the lease in numbers of days.
hours	(Optional) Specifies the number of hours in the lease. A days value must be supplied before you can configure an hours value.
minutes	(Optional) Specifies the number of minutes in the lease. A days value and an hours value must be supplied before you can configure a minutes value.
infinite	Specifies the duration of the lease is unlimited.

address	Specifies the IP address of the NetBIOS WINS name server. One IP address is required, although you can specify up to eight addresses in one command line.
address2...address8	(Optional) Specifies up to eight addresses in the command line.

network-number	The IP address of the DHCP address pool.
mask	(Optional) The bit combination that renders which portion of the address of the DHCP address pool refers to the network or subnet and which part refers to the host.
prefix-length	(Optional) Specifies the number of bits that comprise the address prefix. The prefix is an alternative way of specifying the network mask of the client. The prefix length must be proceeded by a forward slash (/).

address	Specifies the IP address of the next server in the boot process, which is typically a Trivial File Transfer Protocol (TFTP) server. One IP address is required, although you can specify up to eight addresses in one command line.
address2...address8	(Optional) Specifies up to eight addresses in the command line.

Command	Description
bootfile	Specifies the name of the default boot image for a DHCP client.
ip dhcp pool	Configures a DHCP address pool on a Cisco IOS DHCP Server and places you in DHCP pool configuration mode.
ip helper-address	Forwards UDP broadcasts, including BOOTP, received on an interface.
option	Configures Cisco IOS DHCP Server options.

code	Specifies the DHCP option code.
instance number	(Optional) Specifies a number from 0 to 255.
ascii string	Specifies an NVT ASCII character string. ASCII character strings that contain white space must be deliminated by quotation marks.
hex string	Specifies dotted-hexadecimal data. Each byte in hexidecimal character strings is two hexidecimal digits---each byte can be separated by a period, colon, or white space.
ip address	Specifies an IP address.

Field	Description
IP address	The IP address of the host as recorded on the DHCP server.
Hardware address	The MAC address or client identifier of the host as recorded on the DHCP server.
Lease expiration	The lease expiration date of the IP address of the host.
Type	The manner in which the IP address was assigned to the host.

Field	Description
IP Address	The IP address of the host as recorded on the DHCP server.
Detection Method	The manner in which the IP address of the hosts were found on the DHCP server. Can be a ping or a gratuitous ARP.
Detection time	The time when the conflict was found.

Field	Description
URL	Specifies the remote file used to store automatic DHCP bindings. Following are the acceptable URL file formats: tftp://host/filename ftp://user:password@host/filename rcp://user@host/filename
Read	The last time bindings were read from the file server.
Written	The last time bindings were written to the file server.
Status	Indication of whether the last read or write of host bindings was successful.
Delay	The amount of time to wait before updating the database.
Timeout	The amount of time before the file transfer is aborted.
Failures	The number of failed file transfers.
Successes	The number of successful file transfers.

Field	Description
Memory usage	The number of bytes of RAM allocated by the DHCP server.
Address pools	The number of configured address pools in the DHCP database.
Database agents	The number of database agents configured in the DHCP database.
Automatic bindings	The number of IP addresses that have been automatically mapped to the MAC addresses of hosts that are found in the DHCP database.
Manual bindings	The number of IP addresses that have been manually mapped to the MAC addresses of hosts that are found in the DHCP database.
Expired bindings	The number of expired leases.
Malformed messages	The number of truncated or corrupted messages that were received by the DHCP server.
Message	The DHCP message type that was received by the DHCP server.
Received	The number of DHCP messages that were received by the DHCP server.
Sent	The number of DHCP messages that were sent by the DHCP server.

Table of Contents

DHCP Commands