4.4. DHCP Server Commands

Command Purpose

To enable or disable the DHCP snooping, server and relay agent features on your router, use the service dhcp command in Global Config mode.

To disable these functions, use the no form of this command.

Prerequisites

Command Syntax

service dhcp enable

service dhcp disable

Command Mode

Global Config

Default

DHCP service is disabled.

Usage

Only the main DHCP service is enabled by the service dhcp command, can other DHCP services be used, such as dhcp relay, dhcp server and dhcp snooping.

Examples

The following example enables dhcp service:

Switch# configure terminal
Switch(config)# service dhcp enable

The following example disables dhcp service:

Switch# configure terminal
Switch(config)# service dhcp disable

Related Commands

dhcp server

dhcp relay

dhcp snooping

Command Purpose

To enable the DHCP server service, use the dhcp server command in global configuration mode.

To disable this function, use the no form of this command.

Prerequisites

Command Syntax

dhcp server

no dhcp server

Command Mode

Global Config

Default

DHCP server is disabled.

Usage

The DHCP service must be enabled with the dhcp server command before DHCP server service can be used.

Examples

The following is sample output from the dhcp server command:

Switch# configure terminal
Switch(config)# dhcp server

Related Commands

service dhcp

dhcp-server (interface)

Command Purpose

To specify a L3 interface to act as a DHCP Server, use the dhcp server command in interface configuration mode. To remove the specification, use the no form of this command.

Prerequisites

Command Syntax

dhcp server enable

dhcp server disable

Command Mode

Interface Configuration

Default

Neither DHCP server nor DHCP relay is specified.

Usage

This command is used to specify a L3 interface to act as a DHCP Server.

Examples

The following is sample output from the dhcp server command:

Switch# configure terminal
Switch(config)# interface eth-0-1
Switch(config-if)# dhcp server enable

Related Commands

service dhcp

dhcp server(global)

Command Purpose

To configure how many ping packets that are sent before assigning the address to a requesting client, use the dhcp ping packets command in interface configuration mode. To restore the default value, use the no form of this command.

Prerequisites

Command Syntax

dhcp ping packets NUMBER

no dhcp ping packets

Command Mode

Global Config

Default

The default value is one packet.

Usage

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 is sample output from the dhcp ping packets command:

Switch# configure terminal
Switch(config)# dhcp ping packets 10

Related Commands

service dhcp

dhcp ping timeout

Command Purpose

To configure how long a DHCP server waits for a ping reply from an address pool; use the dhcp ping timeout command in interface configuration mode.

To restore the default value, use the no form of this command.

Prerequisites

Command Syntax

dhcp ping timeout NUMBER

no dhcp ping timeout

Command Mode

Global Config

Default

The default value is waiting for one second.

Usage

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 is sample output from the dhcp ping timeout command:

Switch# configure terminal
Switch(config)# dhcp ping timeout 3

Related Commands

service dhcp

dhcp ping packets

Command Purpose

To configure the information reforwarding policy for a DHCP relay agent (what a relay agent should do if a message already contains relay information), use the dhcp relay information policy command in global configuration.

To restore the default relay information policy, use the no form of this command.

Prerequisites

Command Syntax

dhcp pool WORD

no dhcp pool WORD

Command Mode

Global Config

Default

The default value is DHCP address pools are not configured.

Usage

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 is sample output from the dhcp pool command:

Switch# configure terminal
Switch(config)# dhcp pool pool1

Related Commands

service dhcp

dhcp select

static-bind

dhcp excluded-address

network (DHCP)

Command Purpose

To specify an address binding mapping between the IP address and MAC address of a client, use the static-bind pool configuration command. To remove the address binding mapping, use the no form of this command.

Prerequisites

Command Syntax

static-bind ip-address IP_ADDR/IP_MASK_LEN ( mac-address MAC_ADDR | client-identifier ( ascii WORD | hex HEX_STRING ) )

static-bind ip-address IP_ADDR IP_ADDR_MASK ( mac-address MAC_ADDR | client-identifier ( ascii WORD | hex HEX_STRING ) )

no static-bind

Command Mode

DHCP pool Configuration

Default

The default value is none address binding mapping specified.

Usage

You can only configure one manual binding per host pool.

Examples

The following is sample output from the static-bind command:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# static-bind ip 10.10.10.10/24 mac-address 0058.3f22.2222

Related Commands

dhcp pool

Command Purpose

To specify the DNS IP servers available to a DHCP client, use the dns-server DHCP pool configuration command. To remove the DNS server list, use the no form of this command.

Prerequisites

Command Syntax

dns-server A.B.C.D ( A.B.C.D… A.B.C.D )

no dns-server

Command Mode

DHCP pool Configuration

Default

The default value is none DNS IP servers specified.

Usage

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 is sample output from the dns-server command:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# dns-server 1.1.1.1 2.2.2.2

Related Commands

dhcp pool

Command Purpose

To specify the domain name for a DHCP client, use the domain-name DHCP pool configuration command. To remove the domain name, use the no form of this command.

Prerequisites

Command Syntax

domain-name WORD

no domain-name

Command Mode

DHCP pool Configuration

Default

The default value is none domain-name specified.

Usage

You can specify a domain name suffix in each DHCP address pool on the DHCP serverfor the clients. With this suffix assigned, the client needs only input part of a domainname, and the system will add the domain name suffix for name resolution.

Examples

The following is sample output from the domain-name command:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# domain-name switch.org

Related Commands

dhcp pool

Command Purpose

To specify the name of the default boot image for a DHCP client, use the bootfile-name DHCP pool configuration command. To delete the boot image name, use the no form of this command.

Prerequisites

Command Syntax

bootfile-name WORD

no bootfile-name

Command Mode

DHCP pool Configuration

Default

The default value is none boot file specified.

Usage

This task is to specify the IP address and name of a TFTP server and the bootfile name in the DHCP address pool. The DHCP clients use these parameters to contact the TFTP server, requesting the configuration file used for system initialization, which is called autoconfiguration.

Examples

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

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# bootfile dhclient_startup_config

Related Commands

dhcp pool

tftp-server-address

Command Purpose

To configure the tftp server in the boot process of a DHCP client, use the tftp-server-address DHCP pool configuration command. To remove the boot server list, use the no form of this command.

Prerequisites

Command Syntax

tftp-server-address A.B.C.D ( A.B.C.D… A.B.C.D )

no tftp-server-address

Command Mode

DHCP pool Configuration

Default

The default value is none tftp-server-address specified.

Usage

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 is sample output from the tftp-server-address command:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# tftp-server-address 1.1.1.1 2.2.2.2

Related Commands

dhcp pool

bootfile-name

Command Purpose

To specify the default router list for a DHCP client, use the gateway DHCP pool configuration command. To remove the default router list, use the no form of this command.

Prerequisites

Command Syntax

gateway A.B.C.D ( A.B.C.D… A.B.C.D )

no gateway

Command Mode

DHCP pool Configuration

Default

The default value is none gateway servers specified.

Usage

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 is sample output from the gateway command:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# gateway 1.1.1.1 2.2.2.2

Related Commands

dhcp pool

Command Purpose

To specify the default router list for a DHCP client, use the netbios-name-server DHCP pool configuration command. To remove the default router list, use the no form of this command.

Prerequisites

Command Syntax

netbios-name-server A.B.C.D ( A.B.C.D… A.B.C.D )

no netbios-name-server

Command Mode

DHCP pool Configuration

Default

The default value is none NetBIOS WINS name servers specified.

Usage

You can specify up to eight NetBIOS WINS name servers in the list. NetBIOS WINS name 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 is sample output from the netbios-name-server command:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# netbios-name-server 1.1.1.1 2.2.2.2

Related Commands

dhcp pool

Command Purpose

To configure the NetBIOS node type for DHCP clients, use the netbios-node-type DHCP pool configuration command.

To remove the NetBIOS node type, use the no form of this command.

Prerequisites

Command Syntax

netbios-node-type [ b-node | p-node | m-node | h-node ]

no netbios-node-type

Command Mode

DHCP pool Configuration

Default

The default value is none NetBIOS node type specified.

Usage

You can specify the NetBIOS node type for a DHCP address pool which is used to specify the NetBIOS node type for a DHCP Client.

Examples

The following is sample output from the netbios-node-type command:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# netbios-node-type h-node

Related Commands

dhcp pool

Command Purpose

To configure the subnet number and mask for a DHCP address pool on a DHCP Server, use the network DHCP pool configuration command.

To remove the subnet number and mask, use the no form of this command.

Prerequisites

Command Syntax

network [ ip-address wildcard-mask | ip-address/prefix-length ]

no network

Command Mode

DHCP pool Configuration

Default

The default value is none subnet number and mask specified.

Usage

This command is valid for DHCP subnetwork address pools only.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.Network for one pool cann’t the same with other pool’s network and can’t configure manual bindings within the same pool that is configured with the network command.

Examples

The following is sample output from the netbios-node-type command:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# network 1.1.1.0/24

Related Commands

dhcp pool

Command Purpose

To configure the duration of the lease for an IP address that is assigned from a 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.

Prerequisites

Command Syntax

lease DAYS ( HOURS ( MINUTES | ) | )

no lease

Command Mode

DHCP pool Configuration

Default

The default value is one day.

Usage

N/A

Examples

The following example shows a two-day lease:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# lease 2

The following example shows a one-day and two-hour lease:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# lease 1 2

The following example shows a thirty-minute lease:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# lease 0 0 30

Related Commands

dhcp pool

Command Purpose

To configure DHCP Server options, use the option DHCP pool configuration command.

To remove the options, use the no form of this command.

Prerequisites

Command Syntax

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

no option [ code ]

Command Mode

DHCP pool Configuration

Default

The default value is none DHCP option specified.

Usage

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 is sample output from the option command:

Switch# configure terminal
Switch(config)# dhcp pool test
Switch(config-dhcp)# option 43 ip 192.168.1.1

Related Commands

dhcp pool

Command Purpose

To specify a single IP address or a range of IP addresses which the DHCP Server is not assign to DHCP clients, use the excluded-address DHCP pool configuration command. To remove the IP addresses, use the no form of this command.

Prerequisites

Command Syntax

dhcp excluded-address A.B.C.D [ A.B.C.D ]

no dhcp excluded-address A.B.C.D [ A.B.C.D ]

Command Mode

Global Config

Default

All IP pool addresses are assignable.

Usage

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 shows how to disallow DHCP server distribute the address in the range of 10.10.1.100 -10.10.1.199:

Switch# configure terminal
Switch(config-dhcp)# dhcp excluded-address 10.10.1.100 10.10.1.199

Related Commands

dhcp pool

Command Purpose

To display address conflicts found by a DHCP Server when addresses are offered to the client, use the show dhcp server conflict in privileged EXEC mode.

Prerequisites

Command Syntax

show dhcp server conflict [ ip A.B.C.D | all ]

Command Mode

Privileged EXEC

Default

None

Usage

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:

Switch# show dhcp server conflict all

Related Commands

clear dhcp server conflict

dhcp ping packets

dhcp ping timeout

Command Purpose

To display address bindings on a DHCP Server, use the show dhcp server binding in privileged EXEC command.

Prerequisites

Command Syntax

show dhcp server binding [ ip A.B.C.D | pool WORD | all ]

Command Mode

Privileged EXEC

Default

None

Usage

The binding address parameters including an IP address, an associated MAC address, a lease expiration date, and the type of address assignment that have occurred.

Examples

The following examples show the DHCP binding address parameters:

Switch# show dhcp server binding ip 1.1.1.1

Related Commands

clear dhcp server binding

Command Purpose

To display DHCP Server statistics, use the show dhcp server statistics in privileged EXEC command.

Prerequisites

Command Syntax

show dhcp server statistics

Command Mode

Privileged EXEC

Default

None

Usage

N/A

Examples

The following example displays DHCP server statistics:

Switch#show dhcp server statistics

DHCP server packet statistics:
============================================================
Message Received
BOOTREQUEST         12
DHCPDISCOVER        200
DHCPREQUEST         178
DHCPDECLINE         0
DHCPRELEASE         0
DHCPINFORM          0
Message Sent
BOOTREPLY           12
DHCPOFFER           190
DHCPACK             172
DHCPNAK             6

Related Commands

clear dhcp server statistics

Command Purpose

To clear an address conflict from the DHCP server database, use the clear dhcp server conflict privileged EXEC command.

Prerequisites

Command Syntax

clear dhcp server conflict [ ip A.B.C.D | all ]

Command Mode

Privileged EXEC

Default

None

Usage

N/A

Examples

The following example shows an address conflict of 1.1.1.99 being deleted from the DHCP server database:

Switch# clear dhcp server conflict ip 1.1.1.99

Related Commands

show dhcp server conflict

Command Purpose

To delete an automatic address binding from the DHCP Server database, use the clear dhcp server binding in privileged EXEC command.

Prerequisites

Command Syntax

clear dhcp server binding [ ip A.B.C.D | pool WORD | all ]

Command Mode

Privileged EXEC

Default

None

Usage

N/A

Examples

The following example deletes the address binding 1.1.1.99 from a DHCP server database:

Switch# clear dhcp server binding 1.1.1.99

Related Commands

show dhcp server binding

Command Purpose

To reset all DHCP server counters, use the clear dhcp server statistics privileged EXEC command.

Prerequisites

Command Syntax

clear dhcp server statistics

Command Mode

Privileged EXEC

Default

None

Usage

N/A

Examples

The following example resets all DHCP counters to zero:

Switch# clear dhcp server statistics

Related Commands

clear dhcp server statistics

Command Purpose

To display utilization of pool resources, use the show dhcp server pool in privileged EXEC mode.

Prerequisites