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Cisco IOS IP Addressing Services Command Reference
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Introduction
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ARP Commands
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DHCP Commands: accounting (DHCP) through ip dhcp excluded-address
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DHCP Commands: ip dhcp limit lease through lease
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DHCP Commands: netbios-name-server through vrf (DHCP pool)
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DNS Commands: ddns (DDNS-update-method) through ip dns server queue limit
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DNS Commands: ip dns spoofing through view (DNS)
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IP Addressing Commands
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NAT Commands
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NHRP Commands
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Table Of Contents
clear ip dhcp server statistics
clear ip dhcp snooping binding
clear ip dhcp snooping database statistics
clear ip dhcp snooping statistics
ip dhcp client authentication key-chain
ip dhcp client authentication mode
ip dhcp-client default-router distance
ip dhcp-client network-discovery
ip dhcp compatibility lease-query client
ip dhcp compatibility suboption link-selection
DHCP Commands
accounting (DHCP)
To enable Dynamic Host Configuration Protocol (DHCP) accounting, use the accounting command in DHCP pool configuration mode. To disable DHCP accounting for the specified server group, use the no form of this command.
accounting server-group-name
no accounting server-group-name
Syntax Description
Defaults
No default behavior or values
Command Modes
DHCP pool configuration
Command History
Usage Guidelines
The accounting command is used to enable the DHCP accounting feature by sending secure DHCP START accounting messages when IP addresses are assigned to DHCP clients, and secure DHCP STOP accounting messages when DHCP leases are terminated. A DHCP lease is terminated when the client explicitly releases the lease, when the session times out, and when the DHCP bindings are cleared from the DHCP database. DHCP accounting is configured on a per-client or per-lease basis. Separate DHCP accounting processes can be configured on a per-pool basis.
The accounting command can be used to network pools in which bindings are created automatically and destroyed upon lease termination (or when the client sends a DHCP RELEASE message). DHCP bindings are also destroyed when the clear ip dhcp binding or no service dhcp command is issued. These commands should be used with caution if an address pool is configured with DHCP accounting.
The accounting feature can also be used in relay pools. This feature is enabled by using the accounting command with relay pools that use the relay destination command in DHCP pool configuration mode.
AAA and RADIUS must be configured before this command can be used to enable DHCP accounting. A server group must be defined with the aaa group server command. START and STOP message generation is configured with the aaa accounting command. The aaa accounting command can be configured to enable the DHCP accounting to send both START and STOP messages or STOP messages only.
Examples
The following example configures DHCP accounting start and stop messages to be sent if RADIUS-GROUP1 is configured as a start-stop group. Stop messages will only be sent if RADIUS-GROUP1 is configured as a stop-only group.
ip dhcp pool WIRELESS-POOLaccounting RADIUS-GROUP1The following example configures DHCP accounting for a relay pool. The DHCP relay agent sends start and stop messages when an address is assigned to or released from the client.
ip dhcp pool RELAY-POOLrelay source 10.0.0.0 255.0.0relay destination 10.5.5.5accounting RADIUS-GROUP1Related Commands
address client-id
To reserve an IP address for a DHCP client identified by client identifier, use the address client-id command in DHCP pool configuration mode. To remove the reserved address, use the no form of this command.
address ip-address client-id string [ascii]
no address ip-address client-id string [ascii]
Syntax Description
ip-address
IP address reserved for the client.
string
A unique ASCII string or hexadecimal string.
ascii
(Optional) Client ID is in ASCII string form.
Command Default
IP addresses are not reserved.
Command Modes
DHCP pool configuration (dhcp-config)
Command History
Usage Guidelines
The address client-id command can be used to create reserved addresses in pools for any DHCP client identified by the client identifier option in the DHCP packet. You can also reserve an IP address for a DHCP client that is configured to use the port-based address allocation feature. For port-based address allocation, the string argument must be the short name of the interface (port) and the ascii keyword must be specified.
Examples
In the following example, a subscriber ID will be automatically generated based on the short name of the interface (port) specified by the address client-id command. The DHCP server will ignore any client identifier fields in the DHCP messages and use this subscriber ID as the client identifier. The DHCP client is preassigned IP address 10.1.1.7.
ip dhcp use subscriber-id client-idip dhcp subscriber-id interface-nameip dhcp excluded-address 10.1.1.1 10.1.1.3ip dhcp pool dhcppoolnetwork 10.1.1.0 255.255.255.0address 10.1.1.7 client-id ethernet 1/0 asciiRelated Commands
address hardware-address
Reserves an IP address for a client identified by hardware address.
address hardware-address
To reserve an IP address for a client identified by hardware address, use the address hardware-address command in DHCP pool configuration mode. To remove the reserved address, use the no form of this command.
address ip-address hardware-address mac-address [hardware-number]
no address ip-address hardware-address mac-address
Syntax Description
Command Default
IP addresses are not reserved.
Command Modes
DHCP pool configuration (dhcp-config)
Command History
Usage Guidelines
This command is used to reserve an IP address for clients identified by the hardware address included in the fixed-size header of the DHCP message.
Examples
In the following example, an IP address is reserved for a client that is identified by its hardware address:
address 10.10.10.3 hardware-address b708.1388.f166Related Commands
address client-id
Reserves an IP address for a DHCP client identified by the client identifier.
address range
To set an address range for a Dynamic Host Configuration Protocol (DHCP) class in a DHCP server address pool, use the address range command in DHCP pool class configuration mode. To remove the address range, use the no form of this command.
address range start-ip end-ip
no address range start-ip end-ip
Syntax Description
start-ip
Starting IP address that defines the range of addresses in the address pool.
end-ip
Ending IP address that defines the range of addresses in the address pool.
Defaults
No default behavior or values
Command Modes
DHCP pool class configuration
Command History
Usage Guidelines
If this command is not configured for a DHCP class in a DHCP server address pool, the default value is the entire subnet of the address pool.
Examples
The following example sets the available address range for class 1 from 10.0.20.1 through 10.0.20.100:
ip dhcp pool ABCnetwork 10.0.20.0 255.255.255.0class CLASS1address range 10.0.20.1 10.0.20.100Related Commands
authorization username (dhcp)
To specify the parameters that RADIUS sends to a DHCP server when downloading configuration information for a DHCP client, use the authorization username command in DHCP pool configuration mode. To disable the parameters, use the no form of this command.
authorization username string
no authorization username string
Syntax Description
Command Default
Parameters are not specified.
Command Modes
DHCP pool configuration (config-dhcp)
Command History
Examples
The following example shows how to configure RADIUS to send the Ethernet address of the DHCP client (chaddr field) to the DHCP server when downloading configuration information for a DHCP client:
Router(config)# ip dhcp pool pool_commonRouter(config-dhcp)# authorization method auth1Router(config-dhcp)# authorization shared-password ciscoRouter(config-dhcp)# authorization username %c-user1Related Commands
bootfile
To specify the name of the default boot image for a Dynamic Host Configuration Protocol (DHCP) client, use the bootfile command in DHCP pool configuration mode. To delete the boot image name, use the no form of this command.
bootfile filename
no bootfile
Syntax Description
Defaults
No default behavior or values.
Command Modes
DHCP pool configuration
Command History
Examples
The following example specifies xllboot as the name of the boot file:
bootfile xllbootRelated Commands
class (dhcp)
To associate a class with a Dynamic Host Configuration Protocol (DHCP) address pool and enter DHCP pool class configuration mode, use the class command in DHCP pool configuration mode. To remove the class association, use the no form of this command.
class class-name
no class class-name
Syntax Description
Defaults
No default behavior or values
Command Modes
DHCP pool configuration
Command History
Usage Guidelines
You first define the class using the ip dhcp class global configuration command. If a nonexistent class is named by the class command, the class will be automatically created. Each class in the DHCP pool will be examined for a match in the order configured.
Examples
The following example associates DHCP class 1 and class 2 with a DHCP pool named ABC:
ip dhcp pool ABCnetwork 10.0.20.0 255.255.255.0class CLASS1address range 10.0.20.1 10.0.20.100class CLASS2address range 10.0.20.101 10.0.20.200Related Commands
clear ip dhcp binding
To delete an automatic address binding from the Dynamic Host Configuration Protocol (DHCP) server database, use the clear ip dhcp binding command in privileged EXEC mode.
clear ip dhcp [pool name] binding {* | address}
Syntax Description
pool name
(Optional) Name of the DHCP pool.
*
Clears all automatic bindings.
address
The address of the binding you want to clear.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
Typically, the address denotes the IP address of the client. 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.
Note the following behavior for the clear ip dhcp binding command:
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If you do not specify the pool name option and an IP address is specified, it is assumed that the IP address is an address in the global address space and will look among all the non-virtual routing and forwarding (VRF) DHCP pools for the specified binding.
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Examples
he following example deletes the address binding 10.12.1.99 from a DHCP server database:
Router# clear ip dhcp binding 10.12.1.99The following example deletes all bindings from all pools:
Router# clear ip dhcp binding *The following example deletes all bindings from the address pool named pool1:
Router# clear ip dhcp pool pool1 binding *The following example deletes address binding 10.13.2.99 from the address pool named pool2:
Router# clear ip dhcp pool abc binding pool2Related Commands
clear ip dhcp conflict
To clear an address conflict from the Dynamic Host Configuration Protocol (DHCP) server database, use the clear ip dhcp conflict command in privileged EXEC mode.
clear ip dhcp [pool name] conflict {* | address}
Syntax Description
pool name
(Optional) Name of the DHCP pool.
*
Clears all address conflicts.
address
The IP address of the host that contains the conflicting address you want to clear.
Command Modes
Privileged EXEC
Command History
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.
Note the following behavior for the clear ip dhcp conflict command:
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Examples
The following example shows an address conflict of 10.12.1.99 being deleted from the DHCP server database:
Router# clear ip dhcp conflict 10.12.1.99The following example deletes all address conflicts from all pools:
Router# clear ip dhcp conflict *The following example deletes all address conflicts from the address pool named pool1:
Router# clear ip dhcp pool pool1 conflict *The following example deletes address conflict 10.13.2.99 from the address pool named pool2:
Router# clear ip dhcp pool pool2 conflict 10.13.2.99Related Commands
show ip dhcp conflict
Displays address conflicts found by a Cisco IOS DHCP server when addresses are offered to the client.
clear ip dhcp limit lease
To clear lease limit violation entries, use the clear ip dhcp limit lease command in privileged EXEC mode.
clear ip dhcp limit lease [interface-type interface-number]
Syntax Description
Command Modes
Privileged EXEC (#)
Command History
Usage Guidelines
The show ip dhcp limit lease command displays the number of lease limit violations. You can control the number of subscribers at the global level by using the ip dhcp limit lease per interface command and at the interface level by using the ip dhcp limit lease command.
Examples
In the following example, the number of lease violations is displayed and then cleared:
Router# show ip dhcp limit leaseInterface CountSerial0/0.1 5Serial1 3Router# clear ip dhcp limit leaseRouter# show ip dhcp limit leaseRelated Commands
clear ip dhcp server statistics
To reset all Dynamic Host Configuration Protocol (DHCP) server counters, use the clear ip dhcp server statistics command in privileged EXEC mode.
clear ip dhcp server statistics
Syntax Description
This command has no arguments or keywords.
Command Modes
Privileged EXEC
Command History
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 the clear ip dhcp server statistics command.
Examples
The following example resets all DHCP counters to zero:
Router# clear ip dhcp server statisticsRelated Commands
clear ip dhcp snooping binding
To clear the DHCP-snooping binding-entry table without disabling DHCP snooping, use the clear ip dhcp snooping binding command in privileged EXEC mode.
clear ip dhcp snooping binding
Syntax Description
This command has no arguments or keywords.
Defaults
This command has no default settings.
Command Modes
Privileged EXEC
Command History
Examples
This example shows how to clear the DHCP-snooping binding-entry table:
Router# clear ip dhcp snooping bindingclear ip dhcp snooping database statistics
To clear the DHCP binding database statistics, use the clear ip dhcp snooping database statistics command in privileged EXEC mode.
clear ip dhcp snooping database statistics
Syntax Description
This command has no arguments or keywords.
Command Default
This command has no default settings.
Command Modes
Privileged EXEC (#)
Command History
Examples
The following example shows how to clear the statistics from the DHCP binding database:
Router# clear ip dhcp snooping database statisticsclear ip dhcp snooping statistics
To clear the DHCP snooping statistics, use the clear ip dhcp snooping statistics command in privileged EXEC mode.
clear ip dhcp snooping statistics
Syntax Description
This command has no arguments or keywords.
Defaults
This command has no default settings.
Command Modes
Privileged EXEC
Command History
Examples
This example shows how to clear the DHCP snooping statistics:
Router# clear ip dhcp snooping statisticsclear ip dhcp subnet
To clear all currently leased subnets in the Dynamic Host Configuration Protocol (DHCP) pool, use the clear ip dhcp subnet command in privileged EXEC configuration mode.
clear ip dhcp [pool name] subnet { * | address}
Syntax Description
pool name
(Optional) Name of the DHCP pool.
*
Clears all leased subnets.
address
Clears a subnet containing the specified IP address.
Command Modes
Privileged EXEC
Command History
12.2(8)T
This command was introduced.
12.2(33)SRC
This command was integrated into Cisco IOS Release 12.2(33)SRC.
Usage Guidelines
A PPP session that is allocated an IP address from the released subnet will be reset.
Note the following behavior for the clear ip dhcp subnet command:
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Caution
Examples
The following example releases the subnet containing 10.0.0.2 from any non-VRF on-demand address pools:
Router# clear ip dhcp subnet 10.0.0.2The following example clears all leased subnets from all pools:
Router# clear ip dhcp subnet *The following example clears all leased subnets from the address pool named pool3:
Router# clear ip dhcp pool pool3 subnet *The following example clears the address 10.0.0.2 from the address pool named pool2:
Router# clear ip dhcp pool pool2 subnet 10.0.0.2Related Commands
clear ip route dhcp
To remove routes from the routing table added by the Cisco IOS Dynamic Host Configuration Protocol (DHCP) server and relay agent for the DHCP clients on unnumbered interfaces, use the clear ip route dhcp command in EXEC mode.
clear ip route [vrf vrf-name] dhcp [ip-address]
Syntax Description
vrf
(Optional) VPN routing and forwarding instance (VRF).
vrf-name
(Optional) Name of the VRF.
ip-address
(Optional) Address about which routing information should be removed.
Defaults
No default behavior or values.
Command Modes
EXEC
Command History
Usage Guidelines
To remove information about global routes in the routing table, use the clear ip route dhcp command. To remove routes in the VRF routing table, use the clear ip route vrf vrf-name dhcp command.
Examples
The following example removes a route to network 10.5.5.217 from the routing table:
Router# clear ip route dhcp 10.5.5.217Related Commands
show ip route dhcp
Displays the routes added to the routing table by the Cisco IOS DHCP server and relay agent.
client-identifier
To specify the unique identifier (in dotted hexadecimal notation) for a Dynamic Host Configuration Protocol (DHCP) client, use the client-identifier command in DHCP pool configuration mode. 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.
Defaults
No default behavior or values.
Command Modes
DHCP pool configuration
Command History
Usage Guidelines
This command is valid for manual bindings only. 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.
You can determine the client identifier by using the debug ip dhcp server packet command.
Examples
The following example specifies the client identifier for MAC address 01b7.0813.8811.66 in dotted hexadecimal notation:
client-identifier 01b7.0813.8811.66Related Commands
client-name
To specify the name of a Dynamic Host Configuration Protocol (DHCP) client, use the client-name command in DHCP pool configuration mode. 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 abc should not be specified as abc.cisco.com.
Defaults
No default behavior or values
Command Modes
DHCP pool configuration
Command History
Usage Guidelines
The client name should not include the domain name.
Examples
The following example specifies a string client1 that will be the name of the client:
client-name client1Related Commands
default-router
To specify the default router list for a Dynamic Host Configuration Protocol (DHCP) client, use the default-router command in DHCP pool configuration mode. To remove the default router list, use the no form of this command.
default-router address [address2...address8]
no default-router
Syntax Description
Defaults
No default behavior or values.
Command Modes
DHCP pool configuration
Command History
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 10.12.1.99Related Commands
ip dhcp pool
Configures a DHCP address pool on a Cisco IOS DHCP server and enters 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 command in DHCP pool configuration mode. To remove the DNS server list, use the no form of this command.
dns-server address [address2...address8]
no dns-server
Syntax Description
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
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 10.12.1.99Related Commands
domain-name (DHCP)
Specifies the domain name for a DHCP client.
ip dhcp pool
Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode.
domain-name (DHCP)
To specify the domain name for a Dynamic Host Configuration Protocol (DHCP) client, use the domain-name command in DHCP pool configuration mode. To remove the domain name, use the no form of this command.
domain-name domain
no domain-name
Syntax Description
Defaults
No default behavior or values.
Command Modes
DHCP pool configuration
Command History
Examples
The following example specifies cisco.com as the domain name of the client:
domain-name cisco.comRelated Commands
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 enters DHCP pool configuration mode.
hardware-address
To specify the hardware address of a BOOTP client, use the hardware-address command in DHCP pool configuration mode. To remove the hardware address, use the no form of this command.
hardware-address hardware-address [protocol-type | hardware-number]
no hardware-address
Syntax Description
hardware-address
MAC address of the client.
protocol-type
(Optional) Protocol type. The valid entries are:
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If no protocol type is specified, the default is Ethernet.
hardware-number
(Optional) ARP hardware specified in an online database at http://www.iana.org/assignments/arp-parameters. The valid range is from 0 to 255. See Table 14 for valid entries.
Defaults
Only the hardware address is enabled.
Command Modes
DHCP pool configuration
Command History
Usage Guidelines
This command is valid for manual bindings only.
Table 14 lists the valid assigned hardware numbers found online at http://www.iana.org/assignments/arp-parameters.
Examples
The following example specifies b708.1388.f166 as the MAC address of the client:
hardware-address b708.1388.f166 ieee802Related Commands
host
To specify the IP address and network mask for a manual binding to a Dynamic Host Configuration Protocol (DHCP) client, use the host command in DHCP pool configuration mode. To remove the IP address of the client, use the no form of this command.
host address [mask | /prefix-length]
no host
Syntax Description
Defaults
The natural mask is used.
Command Modes
DHCP pool configuration
Command History
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.
There is no limit on the number of manual bindings but you can configure only one manual binding per host pool.
Examples
The following example specifies 10.12.1.99 as the IP address of the client and 255.255.248.0 as the subnet mask:
host 10.12.1.99 255.255.248.0Related Commands
import all
To import Dynamic Host Configuration Protocol (DHCP) option parameters into the DHCP server database, use the import all command in DHCP pool configuration mode. To disable this feature, use the no form of this command.
import all
no import all
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
DHCP pool configuration
Command History
Usage Guidelines
When the no import all command is used, the DHCP server deletes all "imported" option parameters that were added to the specified pool in the server database. Manually configured DHCP option parameters override imported DHCP option parameters.
Imported option parameters are not part of the router configuration and are not saved in NVRAM.
Examples
The following example allows the importing of all DHCP options for a pool named pool1:
ip dhcp pool pool1network 172.16.0.0 /16import allRelated Commands
ip address dhcp
To acquire an IP address on an interface from the Dynamic Host Configuration Protocol (DHCP), use the ip address dhcp command in interface configuration mode. To remove any address that was acquired, use the no form of this command.
ip address dhcp [client-id interface-name] [hostname host-name]
no ip address dhcp [client-id interface-name] [hostname host-name]
Syntax Description
Defaults
The hostname is the globally configured hostname of the router.
The client identifier is an ASCII value.Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
Note
The ip address dhcp command allows any interface to dynamically learn its IP address by using the DHCP protocol. It is especially useful on Ethernet interfaces that dynamically connect to an internet service provider (ISP). Once assigned a dynamic address, the interface can be used with the Port Address Translation (PAT) of Cisco IOS Network Address Translation (NAT) to provide Internet access to a privately addressed network attached to the router.
The ip address dhcp command also works with ATM point-to-point interfaces and will accept any encapsulation type. However, for ATM multipoint interfaces you must specify Inverse ARP via the protocol ip inarp interface configuration command and use only the aa15snap encapsulation type.
Some ISPs require that the DHCPDISCOVER message have a specific hostname and client identifier that is the MAC address of the interface. The most typical usage of the ip address dhcp client-id interface-name hostname host-name command is when interface-name is the Ethernet interface where the command is configured and host-name is the hostname provided by the ISP.
A client identifier (DHCP option 61) can be a hexadecimal or an ASCII value. By default, the client identifier is an ASCII value. The client-id interface option overrides the default and forces the use of the hexadecimal MAC address of the named interface.
Note
If a Cisco router is configured to obtain its IP address from a DHCP server, it sends a DHCPDISCOVER message to provide information about itself to the DHCP server on the network.
If you use the ip address dhcp command with or without any of the optional keywords, the DHCP option 12 field (host name option) is included in the DISCOVER message. By default, the hostname specified in option 12 will be the globally configured host name of the router. However, you can use the ip address dhcp hostname host-name command to place a different name in the DHCP option 12 field than the globally configured hostname of the router.
The no ip address dhcp command removes any IP address that was acquired, thus sending a DHCPRELEASE message.
You might need to experiment with different configurations to determine the one required by your DHCP server. Table 15 shows the possible configuration methods and the information placed in the DISCOVER message for each method.
Examples
In the examples that follow, the command ip address dhcp is entered for Ethernet interface 1. The DISCOVER message sent by a router configured as shown in the following example would contain "cisco- mac-address -Eth1" in the client-ID field, and the value abc in the option 12 field.
hostname abc!interface Ethernet 1ip address dhcpThe DISCOVER message sent by a router configured as shown in the following example would contain "cisco- mac-address -Eth1" in the client-ID field, and the value def in the option 12 field.
hostname abc!interface Ethernet 1ip address dhcp hostname defThe DISCOVER message sent by a router configured as shown in the following example would contain the MAC address of Ethernet 1 interface in the client-id field, and the value abc in the option 12 field.
hostname abc!interface Ethernet 1ip address dhcp client-id Ethernet 1The DISCOVER message sent by a router configured as shown in the following example would contain the MAC address of Ethernet 1 interface in the client-id field, and the value def in the option 12 field.
hostname abc!interface Ethernet 1ip address dhcp client-id Ethernet 1 hostname defRelated Commands
ip dhcp pool
Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode.
ip address pool (DHCP)
To enable the IP address of an interface to be automatically configured when a Dynamic Host Configuration Protocol (DHCP) pool is populated with a subnet from IP Control Protocol (IPCP) negotiation, use the ip address pool command in interface configuration mode. To disable autoconfiguring of the IP address of the interface, use the no form of this command.
ip address pool name
no ip address pool
Syntax Description
name
Name of the DHCP pool. The IP address of the interface will be automatically configured from the DHCP pool specified in name.
Defaults
IP address pooling is disabled.
Command Modes
Interface configuration
Command History
Usage Guidelines
Use this command to automatically configure the IP address of a LAN interface when there are DHCP clients on the attached LAN that should be serviced by the DHCP pool on the router. The DHCP pool obtains its subnet dynamically through IPCP subnet negotiation.
Examples
The following example specifies that the IP address of Ethernet interface 2 will be automatically configured from the address pool named abc:
ip dhcp pool abcimport allorigin ipcp!interface Ethernet 2ip address pool abcRelated Commands
show ip interface
Displays the usability status of interfaces configured for IP.
ip dhcp aaa default username
To specify the default user name for non-virtual routing and forwarding (VRF) address pools that have been configured to obtain subnets through authentication, authorization, and accounting (AAA), use the ip dhcp aaa default username command in global configuration mode. To disable this functionality, use the no form of this command.
ip dhcp aaa default username name
no ip dhcp aaa default username name
Syntax Description
Defaults
No default behavior or values.
Command Modes
Global configuration
Command History
Usage Guidelines
Address pools that are configured with the vrf and origin aaa commands will set the username attribute in the AAA request to the specified VRF name. If the VPN ID as specified in RFC 2685 is configured for the VRF, the VPN ID will be sent instead.
Address pools that are not configured with the vrf command but are configured with the origin aaa command, will set the username attribute in the AAA request to the specified name in the ip dhcp aaa default username command.
Use the debug aaa attribute command to verify the value of the username attribute in the subnet request to the AAA server.
In Cisco IOS Release 12.2(8)T, if this command is not configured, no AAA subnet request from non-VRF ODAPs will be sent.
In Cisco IOS Release 12.2(15)T, if the DHCP pool is not configured with VRF and the ip dhcp aaa default username command is not configured, the AAA request will still be sent with the username attribute set to the DHCP pool name.
This command is not needed if all on-demand address pools (ODAPs) on the VHG/provider edge (PE) are VRF-associated.
Examples
The following example sets the username attribute in the AAA request to abc:
ip dhcp aaa default username abcRelated Commands
ip dhcp bootp ignore
To enable a Dynamic Host Configuration Protocol (DHCP) server to selectively ignore and not reply to received Bootstrap Protocol (BOOTP) request packets, use the ip dhcp bootp ignore command in global configuration mode. To return to the default behavior, use the no form of this command.
ip dhcp bootp ignore
no ip dhcp bootp ignore
Syntax Description
This command has no arguments or keywords.
Defaults
The default behavior is to service BOOTP requests.
Command Modes
Global configuration
Command History
12.2(8)T
This command was introduced.
12.2(28)SB
This command was integrated into Cisco IOS Release 12.2(28)SB.
Usage Guidelines
A DHCP server can forward ignored BOOTP request packets to another DHCP server if the ip helper-address command is configured on the incoming interface. If the ip helper-address command is not configured, the router will drop the received BOOTP request.
Examples
The following example shows that the router will ignore received BOOTP requests:
hostname Router!ip subnet-zero!ip dhcp bootp ignoreRelated Commands
ip bootp server
Enables the BOOTP service on routing devices.
ip helper-address
Forwards UDP broadcasts, including BOOTP, received on an interface.
ip dhcp class
To define a Dynamic Host Configuration Protocol (DHCP) class and enter DHCP class configuration mode, use the ip dhcp class command in global configuration mode. To remove the class, use the no form of this command.
ip dhcp class class-name
no ip dhcp class class-name
Syntax Description
Defaults
No default behavior or values.
Command Modes
Global configuration
Command History
Usage Guidelines
DHCP class configuration provides a method to group DHCP clients based on some shared characteristics other than the subnet in which the clients reside.
Examples
The following example defines three DHCP classes and their associated relay agent information patterns. Note that CLASS3 is considered a "match to any" class because it has no relay agent information pattern configured:
ip dhcp class CLASS1relay agent information! Relay agent information patternsrelay-information hex 01030a0b0c02050000000123relay-information hex 01030a0b0c02*relay-information hex 01030a0b0c02050000000000 bitmask 0000000000000000000000FFip dhcp class CLASS2relay agent information! Relay agent information patternsrelay-information hex 01040102030402020102relay-information hex 01040101030402020102ip dhcp class CLASS3relay agent informationRelated Commands
relay agent information
Enters relay agent information option configuration mode.
relay-information hex
Specifies a hexadecimal string for the full relay agent information option.
ip dhcp client
To configure the Dynamic Host Configuration Protocol (DHCP) client to associate any added routes with a specified tracked object number, use the ip dhcp client command in interface configuration mode. To restore the default setting, use the no form of this command.
ip dhcp client route track number
no ip dhcp client route track
Syntax Description
route track number
Associates a tracked object number with the DHCP-installed static route. Valid values for the number argument range from 1 to 500.
Defaults
No routes are associated with a track number.
Command Modes
Interface configuration
Command History
Usage Guidelines
The ip dhcp client command must be configured before the ip address dhcp command is configured on an interface. The ip dhcp client command is checked only when an IP address is acquired from DHCP. If the ip dhcp client command is specified after an IP address has been acquired from DHCP, the ip dhcp client command will not take effect until the next time the router acquires an IP address from DHCP.
Examples
The following example configures DHCP on an Ethernet interface and associates tracked object 123 with routes generated from this interface:
interface ethernet 0/0ip dhcp client route track 123ip address dhcpRelated Commands
ip dhcp client authentication key-chain
To specify the key chain to be used in authenticating a request, use the ip dhcp client authentication key-chain command in interface configuration mode. To disable key-chain authentication, use the no form of this command.
ip dhcp client authentication key-chain name
no ip dhcp client authentication key-chain name
Syntax Description
Command Default
Authentication is not specified.
Command Modes
Interface configuration (config-if)
Command History
12.4(22)YB
This command was introduced.
15.0(1)M
This command was integrated into Cisco IOS Release 15.0(1)M.
Usage Guidelines
Configure the ip dhcp client authentication key-chain command to send to the server authentication messages that are encoded by the secret ID and secret value that were configured in the key chain command. When authentication is enabled, all client-server exchanges must be authenticated: the ip dhcp client authentication mode and key chain commands must be configured.
Examples
The following example shows how to specify a key chain named chain1 for authentication exchanges:
Router(config-if)# ip dhcp client authentication key-chain chain1Related Commands
ip dhcp client authentication mode
To specify the type of authentication to be used in DHCP messages on the interface, use the ip dhcp client authentication mode command in interface configuration mode. To remove the specification, use the no form of this command.
ip dhcp client authentication mode {md5 | token}
no ip dhcp client authentication mode {md5 | token}
Syntax Description
Command Default
No authentication mode is configured.
Command Modes
Interface configuration (config-if)
Command History
12.4(22)YB
This command was introduced.
15.0(1)M
This command was integrated into Cisco IOS Release 15.0(1)M.
Usage Guidelines
Token-based authentication is useful only for basic protection against inadvertently instantiated DHCP servers. Tokens are transmitted in plain text; they provide weak authentication and do not provide message authentication. MD5-based authentication provides better message and entry authentication because it specifies the generation of a temporary value by the source.
Examples
The following example shows how to specify chain1 as the key chain, and MD5 as the mode, for authentication exchanges:
Router(config-if)# ip dhcp client authentication key-chain chain1Router(config-if)# ip dhcp client authentication mode md5Related Commands
ip dhcp-client broadcast-flag
To configure the Dynamic Host Configuration (DHCP) client to set the broadcast flag, use the ip dhcp-client broadcast-flag command in global configuration mode. To disable this feature, use the no form of this command.
ip dhcp-client broadcast-flag
no dhcp-client broadcast-flag
Syntax Description
This command has no arguments or keywords.
Defaults
The broadcast flag is on.
Command Modes
Global configuration
Command History
Usage Guidelines
Use this command to set the broadcast flag to 1 or 0 in the DHCP packet header when the DHCP client sends a discover requesting an IP address. The DHCP server listens to this broadcast flag and broadcasts the reply packet if the flag is set to 1.
If the no ip dhcp-client broadcast-flag command is entered, the broadcast flag is set to 0 and the DHCP server unicasts the reply packets to the client with the offered IP address.
The DHCP client can receive both broadcast and unicast offers from the DHCP server.
Examples
The following example sets the broadcast flag on:
ip dhcp-client broadcast-flagRelated Commands
ip address dhcp
Acquires an IP address on an interface via DHCP.
service dhcp
Enables DHCP server and relay functions.
ip dhcp client class-id
To specify the class identifier, use the ip dhcp client class-id command in interface configuration mode. To remove the class identifier, use the no form of this command.
ip dhcp client class-id {string | hex string}
no ip dhcp client class-id {string | hex string}
Syntax Description
Defaults
No class identifier is specified.
Command Modes
Interface configuration
Command History
Usage Guidelines
The ip dhcp client class-id command is checked only when an IP address is acquired from a Dynamic Host Configuration Protocol (DHCP) server. If the command is specified after an IP address has been acquired from the DHCP server, the command will not take effect until the next time the router acquires an IP address from the DHCP server. This means that the new configuration will only take effect after either the ip address dhcp command or the release dhcp and renew dhcp EXEC commands have been specified.
The class identifier is used by vendors to specify the type of device that is requesting an IP address. For example, docsis 1.0 can be used for a cable modem and Cisco Systems, Inc. IP Phone can be used for a Cisco IP phone.
Examples
The following example configures a class identifier with a hexadecimal string of ABCDEF1235:
interface Ethernet 1ip dhcp client class-id hex ABCDEF1235Related Commands
ip dhcp-client default-router distance
To configure a default Dynamic Host Configuration Protocol (DHCP) administrative distance for clients, use the ip dhcp-client default-router distance command in global configuration mode. To return to the default, use the no form of this command.
ip dhcp-client default-router distance value
no ip dhcp-client default-router distance value
Syntax Description
distance
DHCP administrative distance. The value argument sets the default distance. The range is from 1 to 255.
Defaults
254
Command Modes
Global configuration
Command History
Examples
The following example shows how to configure the default admininstrative distance to 25:
ip dhcp-client default-router distance 25Related Commands
ip dhcp-client forcerenew
To enable forcerenew-message handling on the DHCP client when authentication is enabled, use the ip dhcp-client forcerenew command in global configuration mode. To disable the forced authentication, use the no form of this command.
ip dhcp-client forcerenew
no ip dhcp-client forcerenew
Syntax Description
This command has no arguments or keywords.
Command Default
Forcerenew messages are dropped.
Command Modes
Global configuration (config)
Command History
12.4(22)YB
This command was introduced.
15.0(1)M
This command was integrated into Cisco IOS Release 15.0(1)M.
Usage Guidelines
DHCP forcerenew handling is not enabled until the CLI is configured.
Examples
The following example shows how to enable DHCP forcerenew-message handling on the DHCP client:
Router(config)# ip dhcp-client forcerenewRelated Commands
ip dhcp client hostname
To specify or modify the hostname sent in a Dynamic Host Configuration Protocol (DHCP) message, use the ip dhcp client hostname command in interface configuration mode. To remove the hostname, use the no form of this command.
ip dhcp client hostname host-name
no ip dhcp client hostname host-name
Syntax Description
Command Default
The hostname is the globally configured hostname of the router.
Command Modes
Interface configuration(config-if)
Command History
Usage Guidelines
The ip dhcp client hostname command is checked only when an IP address is acquired from a DHCP server. If the command is specified after an IP address has been acquired from DHCP, it will not take effect until the next time the router acquires an IP address from the DHCP server. This means that the new configuration will only take effect after either the ip address dhcp command or the release dhcp and renew dhcp EXEC commands have been specified.
This command is applicable only for DHCP requests generated by Cisco IOS software. This command is ignored when Cisco IOS software relays requests (for example, from Distributed Route Processor PPP clients).
Examples
The following example shows how to specify the hostname of the DHCP client as hostA:
interface Ethernet 1ip dhcp client hostname hostARelated Commands
ip dhcp client lease
To configure the duration of the lease for an IP address that is requested from a Dynamic Host Configuration Protocol (DHCP) client to a DHCP server, use the ip dhcp client lease command in interface configuration mode. To restore to the default value, use the no form of this command.
ip dhcp client lease days [hours] [minutes]
no ip dhcp client lease
Syntax Description
Defaults
A default lease time is not included in the DHCP DISCOVER messages sent by the client. The client accepts the lease time that the DHCP server sends.
Command Modes
Interface configuration
Command History
Usage Guidelines
The ip dhcp client lease command is checked only when an IP address is acquired from a DHCP server. If the command is specified after an IP address has been acquired from DHCP, it will not take effect until the next time the router acquires an IP address from the DHCP server. This means that the new configuration will only take effect after either the ip address dhcp command or the release dhcp and renew dhcp EXEC commands have been specified.
Examples
The following example shows a one-day lease:
ip dhcp client lease 1The following example shows a one-hour lease:
ip dhcp client lease 0 1The following example shows a one-minute lease:
ip dhcp client lease 0 0 1Related Commands
ip dhcp client mobile renew
To configure the number of renewal attempts and the interval between attempts for renewing an IP address acquired by a Dynamic Host Configuration Protocol (DHCP) client, use the ip dhcp client mobile renew command in interface configuration mode. To disable the functionality, use the no form of this command.
ip dhcp client mobile renew count number interval ms
no ip dhcp client mobile renew count number interval ms
Syntax Description
Defaults
count number: 2
interval ms: 50Command Modes
Interface configuration
Command History
Usage Guidelines
Mobile DHCP clients automatically attempt to renew an existing IP address in response to certain events, such as moving between wireless access points. The number of renewal attempts, and the interval between those attempts, depending on network conditions, can be modified by using the ip dhcp client mobile renew command.
Examples
In the following example, the DHCP client will make four attempts to renew its current IP address with an interval of 30 milliseconds between attempts :
interface FastEthernet0ip dhcp client mobile renew count 4 interval 30Related Commands
ip dhcp-client network-discovery
To control the sending of Dynamic Host Configuration Protocol (DHCP) Inform and Discover messages, use the ip dhcp-client network-discovery command in global configuration mode. To change or disable DHCP message control, use the no form of this command.
ip dhcp-client network-discovery informs number-of-messages discovers number-of-messages period seconds
no ip dhcp-client network-discovery informs number-of-messages discovers number-of-messages period seconds
Syntax Description
Defaults
0 DHCP Inform and Discover messages (network discovery is disabled when both the informs and discovers keywords are set to 0); 15-second timeout period.
Command Modes
Global configuration
Command History
Usage Guidelines
The ip dhcp-client network-discovery command allows peer routers to dynamically discover Domain Name System (DNS) and NetBIOS name server information configured on a DHCP server using PPP IP Control Protocol (IPCP) extensions. Setting the number of DHCP Inform or Discover messages to 1 or 2 determines how many times the system sends a DHCP Inform or Discover message before stopping network discovery, as follows:
•
•
Network discovery also stops when the DHCP server responds to DHCP Inform and Discover messages before the configured number of messages and timeout period are exceeded.
Setting the number of messages to 0 disables sending of DHCP Inform and Discover messages, and is the same as entering the no ip dhcp-client network-discovery command. When the ip dhcp-client network-discovery command is disabled, the system falls back to the static configurations made using the async-bootp dns-server and async-bootp nb-server global configuration commands or, as a last resort, to a DNS server address assigned with the ip name-server command.
Examples
The following example sets two DHCP Inform and Discovery messages and a timeout period of
12 seconds:ip dhcp-client network-discovery informs 2 discovers 2 period 12Related Commands
ip dhcp client request
To configure a Dynamic Host Configuration Protocol (DHCP) client to request an option from a DHCP server, use the ip dhcp client request command in interface configuration mode. To remove the request for an option, use the no form of this command.
ip dhcp client request option-name
no ip dhcp client request option-name
Syntax Description
Defaults
All the options are requested except sip-server-address, vendor-identifying-specific, and classless-static-route.
Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
By default, all options except sip-server-address, vendor-identifying-specific, and classless-static-route are requested, so you must use the no form of the ip dhcp client request command to disable those default options, and explicitly specify any options that are not enabled by default.
Default options that are specified by the no form are removed from the DHCP originated address for the interface. An option can be reinserted in the list of requested options by using the same command without the no keyword. Multiple options can be specified on one configuration line. However, each option will appear on a separate line in the running configuration.
The ip dhcp client request command is checked only when an IP address is acquired from a DHCP server. If the command is specified after an IP address has been acquired from DHCP, it will not take effect until the next time the router acquires an IP address from the DHCP server. This means that the new configuration will take effect only after either the ip address dhcp command or a DHCP lease renewal or termination that is not initiated by a release dhcp or a renew dhcp command.
Examples
The following example shows how to configure the DHCP client to remove the DNS name server from the options requested from the DHCP server:
no ip dhcp client request dns-nameserverRelated Commands
ip dhcp compatibility lease-query client
To configure the Dynamic Host Configuration Protocol (DHCP) client to send a lease query according to RFC 4388, use the ip dhcp compatibility lease-query client command in global configuration mode. To disable this configuration, use the no form of this command.
ip dhcp compatibility lease-query client {cisco | standard}
no ip dhcp compatibility lease-query client
Syntax Description
Command Default
The DHCP client is configured to use the Cisco standard lease-query message type.
Command Modes
Global configuration (config)
Command History
12.4(22)T
This command was introduced.
12.2(33)SRC
This command was integrated into Cisco IOS Release 12.2(33)SRC.
Usage Guidelines
Some DHCP servers support only the RFC 4388 standard of lease query. If the DHCP server supports only the RFC 4388 standard, then you must configure the DHCP client to send a lease query according to the RFC 4388 standard.
The Cisco IOS DHCP client sends a lease query with the message type set to 13 and receives either an ACK (acknowledge) or NAK (deny) from the DHCP server. This is the behavior of the DHCP client as per the Cisco standard.
As per the RFC 4388 standard, if a DHCP server receives a lease query with the message type set to 10, it will reply with one of the following message types:
•
•
•
By using the ip dhcp compatibility lease-query client command, you can switch between Cisco's implementation and the RFC 4388 standard implementation.
Examples
The following example shows how to configure the DHCP client to switch from Cisco's implementation to the RFC 4388 standard implementation:
Router(config)# ip dhcp compatibility lease-query client standardRelated Commands
ip dhcp compatibility suboption
Configures DHCP compatibility for a relay-agent suboption.
ip dhcp compatibility suboption link-selection
To configure the Dynamic Host Configuration Protocol (DHCP) client to use private as well as the Internet Assigned Numbers Authority (IANA) standard relay agent suboption numbers, use the ip dhcp compatibility suboption link-selection command in global configuration mode. To disable this configuration, use the no form of this command.
ip dhcp compatibility suboption link-selection {cisco | standard}
no ip dhcp compatibility suboption link-selection
Syntax Description
cisco
Configures the DHCP client to use the private Cisco suboption numbers.
standard
Configures the DHCP client to use the standard IANA suboption numbers.
Command Default
Disabled. (The DHCP client is configured to use the private relay agent suboption numbers.)
Command Modes
Global configuration (config)
Command History
12.4(100)
This command was introduced.
12.2(33)SRC
This command was integrated into Cisco IOS Release 12.2(33)SRC.
Usage Guidelines
Sometimes new features are implemented in advance of standardization. That is, features are developed before the IANA numbers are assigned to the relay agent suboptions. In these cases, the DHCP client uses the private Cisco relay agent suboption numbers. When the IANA numbers are assigned later, the DHCP client must be able to use both the private as well as the IANA relay suboption numbers. You can use the ip dhcp compatibility suboption link-selection command to configure the DHCP client to use the IANA relay agent suboption numbers.
Examples
The following example shows how to configure the DHCP client to support the relay agent with the IANA standard suboption number:
Router(config)# ip dhcp compatibility suboption link-selection standardRelated Commands
ip dhcp compatibility lease-query client
Configures the DHCP client to send a lease query according to the RFC 4388 standard.
ip dhcp conflict logging
To enable conflict logging on a Dynamic Host Configuration Protocol (DHCP) server, use the ip dhcp conflict logging command in global configuration mode. 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
Usage Guidelines
A DHCP server database agent should be used to store automatic bindings. If a DHCP server database agent is not used, specify the no ip dhcp conflict logging command to disable the recording of address conflicts. By default, the 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 loggingRelated Commands
ip dhcp database
To configure a Cisco IOS Dynamic Host Configuration Protocol (DHCP) server and relay agent to save automatic bindings on a remote host called a database agent, use the ip dhcp database command in global configuration mode. To remove the database agent, use the no form of this command.
ip dhcp database url [timeout seconds | write-delay seconds | write-delay seconds timeout seconds]
no ip dhcp database url
Syntax Description
Defaults
DHCP waits 300 seconds for both a write delay and a timeout.
Command Modes
Global configuration
Command History
Usage Guidelines
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.
The DHCP relay agent can save route information to the same database agents to ensure recovery after reloads.
In the following example, the timeout value and write-delay are specified in two separate command lines:
ip dhcp database disk0:router-dhcp timeout 60ip dhcp database disk0:router-dhcp write-delay 60However, the second configuration overrides the first command line and causes the timeout value to revert to the default value of 300 seconds. To prevent the timeout value from reverting to the default value, configure the following on one command line:
ip dhcp database disk0:router-dhcp write-delay 60 timeout 60Examples
The following example specifies the DHCP database transfer timeout value as 80 seconds:
ip dhcp database ftp://user:password@172.16.1.1/router-dhcp timeout 80The following example specifies the DHCP database update delay value as 100 seconds:
ip dhcp database tftp://172.16.1.1/router-dhcp write-delay 100Related Commands
show ip dhcp database
Displays Cisco IOS DHCP server database agent information.
ip dhcp excluded-address
To specify IP addresses that a Dynamic Host Configuration Protocol (DHCP) server should not assign to DHCP clients, use the ip dhcp excluded-address command in global configuration mode. 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
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 172.16.1.100 172.16.1.199Related Commands
