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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
ip dhcp limit lease per interface
ip dhcp limited-broadcast-address
ip dhcp relay information check
ip dhcp relay information check-reply
ip dhcp relay information option
ip dhcp relay information option-insert
ip dhcp relay information option server-id-override
ip dhcp-relay information option server-override
ip dhcp relay information option subscriber-id
ip dhcp relay information option vpn-id
ip dhcp relay information policy
ip dhcp relay information policy-action
ip dhcp relay information trust-all
ip dhcp relay information trusted
ip dhcp relay source-interface
ip dhcp-relay source-interface
ip dhcp server use subscriber-id client-id
ip dhcp snooping information option
ip dhcp snooping verify mac-address
ip dhcp subscriber-id interface-name
ip dhcp use subscriber-id client-id
ip dhcp limit lease
To limit the number of leases offered to DHCP clients per interface, use the ip dhcp limit lease command in interface configuration mode. To remove the restriction on the number of leases, use the no form of this command.
ip dhcp limit lease lease-limit
no ip dhcp limit lease lease-limit
Syntax Description
Command Default
There is no lease limit on an interface.
Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
The lease limit allows you to control the number of subscribers per interface. The interface configuration will override any global setting specified by the ip dhcp limit lease per interface command. You can display the number of lease violations by using the show ip dhcp limit lease command.
This command is not supported on numbered interfaces. The lease limit can be applied only to an ATM with Routed Bridge Encapsulation (RBE) unnumbered interfaces or serial unnumbered interfaces.
Examples
The following example allows 30 DHCP clients to receive IP addresses. If a 31st DHCP client tries to obtain an IP address, the DHCPDISCOVER messages will not be forwarded to the DHCP server.
!Router(config)# ip dhcp limit lease logRouter(config)# interface Serial0/0Router(config-if)# ip dhcp limit lease 30Related Commands
ip dhcp limit lease log
To enable DHCP lease violation logging when a DHCP lease limit threshold is exceeded, use the ip dhcp limit lease log command in global configuration mode. To disable the lease violation logging of DHCP lease violations, use the no form of this command.
ip dhcp limit lease log
no ip dhcp limit lease log
Syntax Description
This command has no arguments or keywords.
Command Default
DHCP lease violation logging is disabled.
Command Modes
Global configuration (config)
Command History
Usage Guidelines
The ip dhcp limit lease log command logs violations for global- and interface-level lease violations. If this command is configured, any lease limit violations will display in the output of the show ip dhcp limit lease command.
Examples
The following example shows how to enable logging of lease violations:
Router(config)# ip dhcp limit lease logRelated Commands
ip dhcp limit lease per interface
To limit the number of leases offered to Dynamic Host Configuration Protocol (DHCP) clients behind an ATM routed bridge encapsulation (RBE) unnumbered or serial unnumbered interface, use the ip dhcp limit lease per interface command in global configuration mode. To remove the restriction on the number of leases, use the no form of the command.
ip dhcp limit lease per interface lease-limit
no ip dhcp limit lease per interface lease-limit
Syntax Description
Defaults
This functionality is disabled
Command Modes
Global configuration
Command History
12.3(2)T
This command was introduced.
12.2(28)SB
This command was integrated into Cisco IOS Release 12.2(28)SB.
Usage Guidelines
This command is not supported on numbered interfaces. The lease limit can be applied only to ATM with RBE unnumbered interfaces or serial unnumbered interfaces.
Examples
The following example allows three DHCP clients to receive IP addresses. If a fourth DHCP client tries to obtain an IP address, the DHCPDISCOVER messages will not be forwarded to the DHCP server.
ip dhcp limit lease per interface 3ip dhcp limited-broadcast-address
To override a configured network broadcast and have the Dynamic Host Configuration Protocol (DHCP) server and relay agent send an all networks, all nodes broadcast to a DHCP client, use the ip dhcp limited-broadcast-address command in global configuration mode. To disable this functionality, use the no form of this command.
ip dhcp limited-broadcast-address
no ip dhcp limited-broadcast-address
Syntax Description
This command has no arguments or keywords.
Defaults
Default broadcast address: 255.255.255.255 (all ones)
Command Modes
Global configuration
Command History
Usage Guidelines
When a DHCP client sets the broadcast bit in a DHCP packet, the DHCP server and relay agent send DHCP messages to clients using the all ones broadcast address (255.255.255.255). If the ip broadcast-address command has been configured to send a network broadcast, the all ones broadcast set by DHCP is overridden. To remedy this situation, use the ip dhcp limited-broadcast-address command to ensure that a configured network broadcast does not override the default DHCP behavior.
Some DHCP clients can only accept an all ones broadcast and may not be able to acquire a DHCP address unless this command is configured on the router interface connected to the client.
Examples
The following example configures DHCP to override any network broadcast:
ip dhcp limited-broadcast-addressRelated Commands
ip dhcp ping packets
To specify the number of packets a Dynamic Host Configuration Protocol (DHCP) server sends to a pool address as part of a ping operation, use the ip dhcp ping packets command in global configuration mode. To prevent the server from pinging pool addresses, use the no form of this command. To return the number of ping packets sent to the default value, use the default form of this command.
ip dhcp ping packets number
no ip dhcp ping packets
default ip dhcp ping packets
Syntax Description
number
The number of ping packets that are sent before the address is assigned to a requesting client. The default value is two packets.
Defaults
Two packets
Command Modes
Global configuration
Command History
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.
Setting the number argument to a value of 0 completely turns off DHCP server ping operation .
Examples
The following example specifies five ping attempts by the DHCP server before ceasing any further ping attempts:
ip dhcp ping packets 5Related Commands
ip dhcp ping timeout
To specify how long a Dynamic Host Configuration Protocol (DHCP) server waits for a ping reply from an address pool, use the ip dhcp ping timeout command in global configuration mode. 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
Defaults
500 milliseconds
Command Modes
Global configuration
Command History
Usage Guidelines
This command specifies how long to wait for a ping reply (in milliseconds).
Examples
The following example specifies that a DHCP server will wait 800 milliseconds for a ping reply before considering the ping a failure:
ip dhcp ping timeout 800Related Commands
ip dhcp pool
To configure a Dynamic Host Configuration Protocol (DHCP) address pool on a DHCP server and enter DHCP pool configuration mode, use the ip dhcp pool command in global configuration mode. To remove the address pool, use the no form of this command.
ip dhcp pool name
no ip dhcp pool name
Syntax Description
name
Name of the pool. 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
Usage Guidelines
During execution of this command, the configuration mode changes to DHCP pool configuration mode, which is 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 pool1Related Commands
ip dhcp relay bootp ignore
To configure the Dynamic Host Configuration Protocol (DHCP) relay agent stop forwarding Bootstrap Protocol (BOOTP) packets between the clients and servers, use the ip dhcp relay bootp ignore command in global configuration mode. To disable the configuration, use the no form of this command.
ip dhcp relay bootp ignore
no ip dhcp relay bootp ignore
Syntax Description
This command has no arguments or keywords.
Command Default
Disabled (Relay agent forwards BOOTP packets from clients and servers).
Command Modes
Global configuration (config)
Command History
Usage Guidelines
You can use the ip dhcp relay agent bootp ignore command in network deployments, where clients send both BOOTP and DHCP packets. When the client sends both type of packets, sometimes the DHCP server or the relay agent will not be able to differentiate between the two types of packets. You can use this command to configure the relay agent stop forwarding the BOOTP packets.
Examples
The following example shows how to configure the relay agent to stop forwarding BOOTP packets:
Router# configure terminalRouter(config)# ip dhcp relay bootp ignoreRelated Commands
ip dhcp relay information check
To configure a Dynamic Host Configuration Protocol (DHCP) server to validate the relay agent information option in forwarded BOOTREPLY messages, use the ip dhcp relay information check command in global configuration mode. 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
A DHCP server checks relay information. Invalid messages are dropped.
Command Modes
Global configuration
Command History
Usage Guidelines
This command is used by cable access router 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 checkRelated Commands
ip dhcp relay information check-reply
To configure a DHCP server to validate the relay agent information option in forwarded BOOTREPLY messages, use the ip dhcp relay information check-reply command in interface or subinterface configuration mode. To disable an information check, use the no form of this command.
ip dhcp relay information check-reply [none]
no ip dhcp relay information check-reply [none]
Syntax Description
Command Default
A DHCP server checks relay information. Invalid messages are dropped.
Command Modes
Interface configuration
Subinterface configurationCommand History
12.4(6)T
This command was introduced.
12.2(33)SRC
This command was integrated into Cisco IOS Release 12.2(33)SRC.
Usage Guidelines
If an ip dhcp relay information command is configured in global configuration mode but not configured in interface configuration mode, the global configuration is applied to all interfaces.
If an ip dhcp relay information command is configured in both global configuration mode and interface configuration mode, the interface configuration command takes precedence over the global configuration command. However, the global configuration is applied to interfaces without the interface configuration.
If an ip dhcp relay information command is not configured in global configuration mode but is configured in interface configuration mode, only the interface with the configuration option applied is affected. All other interfaces are not impacted by the configuration.
The ip dhcp relay information check-reply none command option is saved in the running configuration. This command takes precedence over any relay agent information global configuration.
Examples
The following example shows how to configure the DHCP server to check that the relay agent information option in forwarded BOOTREPLY messages received from FastEthernet interface 0 is valid:
!interface FastEthernet 0ip dhcp relay information check-replyRelated Commands
ip dhcp relay information option
To enable the system to insert a Dynamic Host Configuration Protocol (DHCP) relay agent information option in forwarded BOOTREQUEST messages to a DHCP server, use the ip dhcp relay information option command in global configuration mode. To disable inserting relay information into forwarded BOOTREQUEST messages, use the no form of this command.
ip dhcp relay information option [vpn]
no ip dhcp relay information option [vpn]
Syntax Description
Command Default
The DHCP server does not insert relay information.
Command Modes
Global configuration
Command History
Usage Guidelines
This functionality enables a DHCP server to identify the user (for example, cable access router) sending a request and initiate appropriate action based on this information. By default, DHCP does not insert relay information.
The ip dhcp relay information option command automatically adds the circuit identifier suboption and the remote ID suboption to the DHCP relay agent information option (also called option 82).
The vpn optional keyword should be used only when the DHCP server allocates addresses based on VPN identification suboptions.
The ip dhcp relay information option vpn command adds the following VPN-related suboptions into the relay agent information option when DHCP broadcasts are forwarded by the relay agent from clients to a DHCP server:
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VPN identifier—Contains the VPN ID if configured or the virtual routing and forwarding (VRF) name if configured on the interface (VPN ID takes precedence over VRF name).
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•
After these suboptions are successfully added, the gateway address is set to the outgoing interface of the router toward the DHCP server IP address that was configured using the ip helper-address command.
If only the ip dhcp relay information option vpn command is configured, the VPN identifier, subnet selection, and server identifier override suboptions are added to the relay information option. Note that the circuit identifier suboption and the remote ID suboption are not added to the relay information option. However, if both the ip dhcp relay information option command and the ip dhcp relay information option vpn command are configured, all five suboptions are added to the relay agent information option.
When the packets are returned from the DHCP server, option 82 is removed before the reply is forwarded to the client.
Even if the vpn option is specified, the VPN suboptions are added only to those DHCP or BOOTP broadcasts picked up by the interface that was configured with a VRF name or VPN ID.
For clients from unnumbered ATM or serial interfaces, when this command is enabled, the VPN identifier suboption will contain the VRF name of the unnumbered interface.
Subnet selection and server identifier override suboptions are added from the IP address of the interface from which the unnumbered interface is configured to borrow its IP address. The client host route will be added on the applicable VRF routing tables.
If the ip dhcp smart-relay global configuration command is enabled, then the server identifier override and subnet selection suboptions will use the secondary IP address of the incoming interface when the same client retransmits more than three DHCP DISCOVER packets (for both numbered and unnumbered interfaces).
Examples
The following example configures a DHCP server to insert the DHCP relay agent information option, including VPN suboptions, in forwarded BOOTREQUEST messages. In this example, the circuit identifier suboption and the remote ID suboption are not included in the relay information option:
ip dhcp relay information option vpnThe following example configures a DHCP server to insert the DHCP relay agent information option, including VPN suboptions, the circuit identifier suboption, and the remote ID suboption, in forwarded BOOTREQUEST messages:
ip dhcp relay information option vpnip dhcp relay information optionCisco 10000 Series Router
The following example enables DHCP option 82 support on the DHCP relay agent by using the ip dhcp relay information option command. The rbe nasip command configures the router to forward the IP address for Loopback0 to the DHCP server. The value (in hexadecimal) of the agent remote ID suboption is 010100000B0101814058320, and the value of each field is the following:
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•
•
•
•
–
–
–
ip dhcp-server 172.16.1.2!ip dhcp relay information option!interface Loopback0ip address 10.1.1.129 255.255.255.192!interface ATM4/0no ip address!interface ATM4/0.1 point-to-pointip unnumbered Loopback0ip helper-address 172.16.1.2atm route-bridged ippvc 88/800encapsulation aal5snap!interface Ethernet 5/1ip address 172.16.1.1 255.255.0.0!router eigrp 100network 10.0.0.0network 172.16.0.0!rbe nasip Loopback0In the following example, the DHCP relay receives a DHCP request on Ethernet interface 0/1 and sends the request to the DHCP server located at IP helper address 10.44.23.7, which is associated with the VRF named red.
ip dhcp relay information option vpn!interface ethernet 0/1ip helper-address vrf red 10.44.23.7Related Commands
ip dhcp relay information option-insert
To enable the system to insert a DHCP relay agent information option in forwarded BOOTREQUEST messages to a DHCP server, use the ip dhcp relay information option-insert command in interface configuration mode or subinterface configuration mode. To disable inserting relay information into forwarded BOOTREQUEST messages, use the no form of this command.
ip dhcp relay information option-insert [none]
no ip dhcp relay information option-insert [none]
Syntax Description
Command Default
The DHCP server does not insert relay information.
Command Modes
Interface configuration
Subinterface configurationCommand History
12.4(6)T
This command was introduced.
12.2(33)SRC
This command was integrated into Cisco IOS Release 12.2(33)SRC.
Usage Guidelines
If an ip dhcp relay information command is configured in global configuration mode but not configured in interface configuration mode, the global configuration is applied to all interfaces.
If an ip dhcp relay information command is configured in both global configuration mode and interface configuration mode, the interface configuration command takes precedence over the global configuration command. However, the global configuration is applied to interfaces without the interface configuration.
If an ip dhcp relay information command is not configured in global configuration mode but is configured in interface configuration mode, only the interface with the configuration option applied is affected. All other interfaces are not impacted by the configuration.
The ip dhcp relay information option-insert none command option is saved in the running configuration. This command takes precedence over any relay agent information global configuration.
Examples
The following example shows how to configure the DHCP server to insert the relay agent information option in forwarded BOOTREQUEST messages:
!interface FastEthernet 0ip dhcp relay information option-insertRelated Commands
ip dhcp relay information option server-id-override
To enable the system to insert the server ID override and link selection suboptions on a specific interface into the DHCP relay agent information option in forwarded BOOTREQUEST messages to a DHCP server, use the ip dhcp relay information option server-id-override command in interface configuration mode. To disable inserting the server ID override and link selection suboptions into the DHCP relay agent information option, use the no form of this command.
ip dhcp relay information option server-id-override
no ip dhcp relay information option server-id-override
Syntax Description
This command has no arguments or keywords.
Command Default
The server ID override and link selection suboptions are not inserted into the DHCP relay agent information option.
Command Modes
Interface configuration (config-if)
Command History
Cisco IOS XE Release 2.1
This feature was introduced on Cisco ASR 1000 Series Routers.
Usage Guidelines
The ip dhcp relay information option server-id-override interface configuration command adds the following suboptions into the relay agent information option when DHCP broadcasts are forwarded by the relay agent from clients to a DHCP server:
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•
When this command is configured, the gateway address (giaddr) will be set to the IP address of the outgoing interface, which is the interface that is reachable by the DHCP server.
If the ip dhcp relay information option server-id-override interface configuration command is configured on an interface, it overrides the ip dhcp-relay information option server-override global configuration on that interface only.
Examples
In the following example, the DHCP relay will insert the server ID override and link selection suboptions into the relay information option on interface Ethernet interface 0/0.
Router(config)# interface Ethernet0/0Router(config-if)# ip dhcp relay information option server-id-overrideRelated Commands
ip dhcp-relay information option server-override
To enable the system to globally insert the server ID override and link selection suboptions into the DHCP relay agent information option in forwarded BOOTREQUEST messages to a DHCP server, use the ip dhcp-relay information option server-override command in global configuration mode. To disable inserting the server ID override and link selection suboptions into the DHCP relay agent information option, use the no form of this command.
ip dhcp-relay information option server-override
no ip dhcp-relay information option server-override
Syntax Description
This command has no arguments or keywords.
Command Default
The server ID override and link selection suboptions are not inserted into the DHCP relay agent information option.
Command Modes
Global configuration (config)
Command History
Cisco IOS XE Release 2.1
This feature was introduced on Cisco ASR 1000 Series Routers.
Usage Guidelines
The ip dhcp-relay information option server-override command adds the following suboptions into the relay agent information option when DHCP broadcasts are forwarded by the relay agent from clients to a DHCP server:
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•
When this command is configured, the gateway address (giaddr) will be set to the IP address of the outgoing interface, which is the interface that is reachable by the DHCP server.
If the ip dhcp relay information option server-id-override interface configuration command is configured on an interface, it overrides the global configuration on that interface only.
Examples
In the following example, the DHCP relay will insert the server ID override and link selection suboptions into the relay information option of the DHCP packet. The loopback interface IP address is configured to be the source IP address for the relayed messages.
!Router(config)# ip dhcp-relay information option server-overrideRouter(config)# ip dhcp-relay source-interface loopback0!Router(config)# interface Loopback0Router(config-if)# ip address 10.2.2.1 255.255.255.0Related Commands
ip dhcp relay information option subscriber-id
To specify that a Dynamic Host Configuration Protocol (DHCP) relay agent add a subscriber identifier suboption to option82, use the ip dhcp relay information option subscriber-id command in interface configuration mode. To disable the subscriber identifier, use the no form of this command.
ip dhcp relay information option subscriber-id string
no ip dhcp relay information option subscriber-id string
Syntax Description
string
Up to a maximum of 50 characters that can be alphanumeric. The string can be ASCII text only.
Note
Defaults
Disabled to allow backward capability.
Command Modes
Interface configuration
Command History
Usage Guidelines
When the unique subscriber identifier is configured on the relay agent and the interface, the identifier is added to option82 in all of the client DHCP packets to the DHCP server. When the server echoes option82 in the reply packets, the relay agent removes option82 before forwarding the reply packet to the client. When an interface is numbered, all renew packets and release packets are unicast to the server, so option82 is not added.
The unique identifier should be configured for each subscriber and when a subscriber moves from one interface to the other, the configuration of the interface should be changed also.
In case of unnumbered interfaces, all the client packets are sent to the relay. Option82 is added in all the client packets before forwarding the packets to the server. If the server does not echo option82 in the packet, the relay agent tries to validate option82 in the reply packet. If the reply packet does not contain option82, then the validation fails and the packet is dropped by the relay agent. The client cannot get any IP address because of the validation failure. In this case, the existing no ip dhcp relay information check command can be used to avoid the option82 invalidation.
Note
Examples
The following example shows how to configure an ATM interface for the subscriber identifier suboption.
ip dhcp relay information option!interface Loopback0ip address 10.1.1.129 255.255.255.192!interface ATM4/0no ip address!interface ATM4/0.1 point-to-pointip helper-address 10.16.1.2ip unnumbered Loopback0ip dhcp relay information option subscriber-id newperson123atm route-bridged ippvc 88/800encapsulation aal5snapRelated Commands
ip dhcp relay information option vpn-id
To enable the system to insert VPN suboptions into the DHCP relay agent information option in forwarded BOOTREQUEST messages to a DHCP server and set the gateway address to the outgoing interface toward the DHCP server, use the ip dhcp relay information option vpn-id command in interface configuration mode. To remove the configuration, use the no form of this command.
ip dhcp relay information option vpn-id [none]
no ip dhcp relay information option vpn-id
Syntax Description
Command Default
The DHCP server does not insert relay information.
Command Modes
Interface configuration
Command History
Usage Guidelines
If the ip dhcp relay information option vpn global configuration command is configured and the ip dhcp relay information option vpn-id interface configuration command is not configured, the global configuration is applied to all interfaces.
If the ip dhcp relay information option vpn global configuration command is configured and the ip dhcp relay information option vpn-id interface configuration command is also configured, the interface configuration command takes precedence over the global configuration command. However, the global configuration is applied to interfaces without the interface configuration.
If the ip dhcp relay information option vpn global configuration command is not configured and the ip dhcp relay information option vpn-id interface configuration command is configured, only the interface with the configuration option applied is affected. All other interfaces are not impacted by the configuration.
The ip dhcp relay information option vpn-id none option allows you to disable the VPN functionality on the interface. The only time you need to use this option is when the ip dhcp relay information option vpn global configuration command is configured and you want to override the global configuration.
The no ip dhcp relay information option vpn-id command removes the configuration from the running configuration. In this case, the interface inherits the global configuration, which may or may not be configured to insert VPN suboptions.
Examples
In the following example, the DHCP relay agent receives a DHCP request on Ethernet interface 0/1 and sends the request to the DHCP server located at IP helper address 10.44.23.7, which is associated with the VRF named red. The ip dhcp relay information option vpn-id interface configuration command only applies to Ethernet interface 0/1. All other interfaces are not impacted by the configuration:
!interface ethernet 0/1ip helper-address vrf red 10.44.23.7ip dhcp relay information option vpn-idRelated Commands
ip dhcp relay information option
Enables the system to insert the DHCP relay agent information option in forwarded BOOTREQUEST messages to a DHCP server.
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 command in global configuration mode. To restore the default relay information policy, use the no form of this command.ip dhcp relay information policy {drop | encapsulate | keep | replace}
no ip dhcp relay information policy
Syntax Description
Defaults
The DHCP server replaces existing relay information.
Command Modes
Global configuration (config)
Command History
Usage Guidelines
A DHCP relay agent may receive a message from another DHCP relay agent that already contains relay information. By default, the relay information from the previous relay agent is replaced.
The ip dhcp relay information policy encapsulate command option is only needed when the relay agent needs to encapsulate the relay agent information option from a prior relay agent. If this command option is used, the prior option 82 is encapsulated inside the current option 82 and both are forwarded to the DHCP server.
Examples
The following examples show how to configure a DHCP relay agent to drop messages with existing relay information, keep existing information, replace existing information, and encapsulate existing information, respectively:
ip dhcp relay information policy dropip dhcp relay information policy keepip dhcp relay information policy replaceip dhcp relay information policy encapsulateRelated Commands
ip dhcp relay information policy-action
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 ip dhcp relay information policy-action command in interface configuration mode or subinterface configuration mode. To restore the default relay information policy, use the no form of this command.
ip dhcp relay information policy-action {drop | encapsulate | keep | replace}
no ip dhcp relay information policy-action {drop | encapsulate | keep | replace}
Syntax Description
Command Default
The DHCP server replaces existing relay information.
Command Modes
Interface configuration
Subinterface configurationCommand History
12.4(6)T
This command was introduced.
12.2(33)SRC
This command was integrated into Cisco IOS Release 12.2(33)SRC.
12.2(33)SRD
The encapsulation keyword was added.
Usage Guidelines
If an ip dhcp relay information command is configured in global configuration mode but not configured in interface configuration mode, the global configuration is applied to all interfaces.
If an ip dhcp relay information command is configured in both global configuration mode and interface configuration mode, the interface configuration command takes precedence over the global configuration command. However, the global configuration is applied to interfaces without the interface configuration.
If an ip dhcp relay information command is not configured in global configuration mode but is configured in interface configuration mode, only the interface with the configuration option applied is affected. All other interfaces are not impacted by the configuration.
The ip dhcp relay information policy-action encapsulate command is only needed when the relay agent needs to encapsulate the relay agent information option from a prior relay agent. If this command option is used, the prior option 82 is encapsulated inside the current option 82 and both are forwarded to the DHCP server.
Examples
The following example shows how to configure a DHCP relay agent to drop messages with existing relay information:
interface FastEthernet 0ip dhcp relay information policy-action dropThe following example shows how to configure a DHCP relay agent to encapsulate existing relay information:
interface Ethernet0/0ip dhcp relay information policy-action encapsulateRelated Commands
ip dhcp relay information trust-all
To configure all interfaces on a router as trusted sources of the Dynamic Host Configuration Protocol (DHCP) relay agent information option, use the ip dhcp relay information trust-all command in global configuration mode. To restore the interfaces to their default behavior, use the no form of the command.
ip dhcp relay information trust-all
no ip dhcp relay information trust-all
Syntax Description
This command has no arguments or keywords.
Defaults
All interfaces on the router are considered untrusted.
Command Modes
Global configuration
Command History
Usage Guidelines
By default, if the gateway address is set to all zeros in the DHCP packet and the relay information option is already present in the packet, the Cisco IOS DHCP relay agent will discard the packet. If the ip dhcp relay information trust-all command is configured globally, the Cisco IOS DHCP relay agent will not discard the packet even if the gateway address is set to all zeros. Instead, the received DHCPDISCOVER or DHCPREQUEST messages will be forwarded to the addresses configured by the ip helper-address command as in normal DHCP relay operation.
Examples
In the following example, all interfaces on the router are configured as a trusted source for relay agent information:
ip dhcp relay information trust-allRelated Commands
ip dhcp relay information trusted
To configure an interface as a trusted source of the Dynamic Host Configuration Protocol (DHCP) relay agent information option, use the ip dhcp relay information trusted command in interface configuration mode. To restore the interface to the default behavior, use the no form of the command.
ip dhcp relay information trusted
no ip dhcp relay information trusted
Syntax Description
This command has no arguments or keywords.
Defaults
All interfaces on the router are considered untrusted.
Command Modes
Interface configuration
Command History
Usage Guidelines
By default, if the gateway address is set to all zeros in the DHCP packet and the relay information option is already present in the packet, the Cisco IOS DHCP relay agent will discard the packet. If the ip dhcp relay information trusted command is configured on an interface, the Cisco IOS DHCP relay agent will not discard the packet even if the gateway address is set to all zeros. Instead, the received DHCPDISCOVER or DHCPREQUEST messages will be forwarded to the addresses configured by the ip helper-address command as in normal DHCP relay operation.
Examples
In the following example, interface Ethernet 1 is configured as a trusted source for the relay agent information:
interface ethernet 1ip dhcp relay information trustedRelated Commands
ip dhcp relay source-interface
To configure the source interface for the relay agent to use as the source IP address for relayed messages, use the ip dhcp relay source-interface command in interface configuration mode. To remove the source interface configuration, use the no form of the command.
ip dhcp relay source-interface type number
no ip dhcp relay source-interface type number
Syntax Description
Command Default
The source interface is not configured.
Command Modes
Interface configuration (config-if)
Command History
Cisco IOS XE Release 2.1
This feature was introduced on Cisco ASR 1000 Series Routers.
Usage Guidelines
The ip dhcp relay source-interface interface configuration command allows the network administrator to specify a stable, hardware-independent IP address (such as a loopback interface) for the relay agent to use as a source IP address for relayed messages.
If the ip dhcp-relay source-interface global configuration command is configured and the ip dhcp relay source-interface interface configuration command is also configured, the interface configuration command takes precedence over the global configuration command. However, the global configuration is applied to interfaces without the interface configuration.
Examples
In the following example, the loopback interface IP address is configured to be the source IP address for the relayed messages on interface GigabitEthernet interface 0:
!Router(config)# interface loopback0Router(config-if)# ip address 10.2.2.1 255.255.255.0!Router(config)# interface GigabitEthernet 0Router(config-if)# ip dhcp relay source-interface loopback0Related Commands
ip dhcp-relay source-interface
Globally configures the source interface for the relay agent to use as the source IP address for relayed messages.
ip dhcp-relay source-interface
To globally configure the source interface for the relay agent to use as the source IP address for relayed messages, use the ip dhcp-relay source-interface command in global configuration mode. To remove the source interface configuration, use the no form of the command.
ip dhcp-relay source-interface type number
no ip dhcp-relay source-interface type number
Syntax Description
Command Default
The source interface is not configured.
Command Modes
Global configuration (config)
Command History
Cisco IOS XE Release 2.1
This feature was introduced on Cisco ASR 1000 Series Routers.
Usage Guidelines
The ip dhcp-relay source-interface global configuration command allows the network administrator to specify a stable, hardware-independent IP address (such as a loopback interface) for the relay agent to use as a source IP address for relayed messages.
If the ip dhcp-relay source-interface global configuration command is configured and the ip dhcp relay source-interface interface configuration command is also configured, the interface configuration command takes precedence over the global configuration command. However, the global configuration is applied to interfaces without the interface configuration.
Examples
In the following example, the loopback interface IP address is configured to be the source IP address for the relayed messages.
!Router(config)# ip dhcp-relay source-interface loopback0!Router(config)# interface loopback0Router(config-if)# ip address 10.2.2.1 255.255.255.0Related Commands
ip dhcp relay source-interface
Configures the source interface for the relay agent to use as the source IP address for relayed messages.
ip dhcp route connected
To specify routes as connected routes, use the ip dhcp route connected command in global configuration mode. To return to the default settings, use the no form of this command.
ip dhcp route connected
no ip dhcp route connected
Syntax Description
This command has no arguments or keywords.
Defaults
All interfaces on the router are untrusted.
Command Modes
Global configuration
Command History
12.2(18)SXF
Support for this command was introduced on the Supervisor Engine 720.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
Usage Guidelines
If you enable the ip dhcp route connected command, DHCP downloads the route database from a database agent and adds the routes as connected routes, even though they may have been added as static routes previously.
Examples
This example shows how to specify routes as connected routes:
Router(config)# ip dhcp route connectedip dhcp-server
To specify which Dynamic Host Configuration Protocol (DHCP) servers to use on your network, or to specify the IP address of one or more DHCP servers available on the network, use the ip dhcp-server command in global configuration mode. To remove a DHCP server IP address, use the no form of this command.
ip dhcp-server [ip-address | name]
no ip dhcp-server [ip-address | name]
Syntax Description
Defaults
The IP limited broadcast address of 255.255.255.255 is used for transactions if no DHCP server is specified. This default allows automatic detection of DHCP servers.
Command Modes
Global configuration
Command History
Usage Guidelines
A DHCP server temporarily allocates network addresses to clients through the access server on an as-needed basis. While the client is active, the address is automatically renewed in a minimum of 20-minute increments. When the user terminates the session, the interface connection is terminated so that network resources can be quickly reused. You can specify up to ten servers on the network.
In normal situations, if a SLIP or PPP session fails (for example, if a modem line disconnects), the allocated address will be reserved temporarily to preserve the same IP address for the client when dialed back into the server. This way, the session that was accidentally terminated can often be resumed.
To use the DHCP proxy-client feature, enable your access server to be a proxy-client on asynchronous interfaces by using the ip address-pool dhcp-proxy-client command. If you want to specify which DHCP servers are used on your network, use the ip dhcp-server command to define up to ten specific DHCP servers.
Note
The ip address-pool dhcp-proxy-client command initializes proxy-client status to all interfaces defined as asynchronous on the access server. To selectively disable proxy-client status on a single asynchronous interface, use the no peer default ip address interface command.
Examples
The following command specifies a DHCP server with the IP address of 172.24.13.81:
ip dhcp-server 172.24.13.81Related Commands
ip dhcp-server query lease
To change the default global retransmission scheme for Dynamic Host Configuration Protocol (DHCP) lease query packets, use the ip dhcp-server query lease command in global configuration mode. To remove this retransmission scheme and return to the default behavior, use the no form of this command.
ip dhcp-server query lease {retries number | timeout seconds}
no ip dhcp-server query lease {retries number | timeout seconds}
Syntax Description
Defaults
retries number : 2
timeout seconds : 5Command Modes
Global configuration
Command History
Usage Guidelines
The DHCP Lease Query protocol is a lightweight mechanism to query a DHCP server for certain information related to IP addresses leased from the DHCP server.
You can specify which DHCP servers to query by using the ip dhcp-server global configuration command. You can specify up to 10 servers on the network. Use the ip dhcp-server query lease global configuration command to change the default global retransmission scheme for lease query packets.
Examples
In the following example, the time to wait for a reply to a lease query is set to 15 seconds:
ip dhcp-server query lease timeout 15In the following example, the retry number is set to 0, which means that only a single DHCP lease query will be transmitted for each DHCP server; no retries will be attempted.
ip dhcp-server query lease retries 0Related Commands
ip dhcp server use subscriber-id client-id
To configure the DHCP server to use the subscriber identifier as the client identifier on all incoming DHCP messages on an interface, use the ip dhcp server use subscriber-id client-id command in interface configuration mode. To disable this functionality, use the no form of this command.
ip dhcp server use subscriber-id client-id
no ip dhcp server use subscriber-id client-id
Syntax Description
This command has no arguments or keywords.
Command Default
DHCP uses the client identifier option in the DHCP packet to identify clients.
Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
This command takes precedence on the interface over the ip dhcp use subscriber-id client-id global configuration command.
Examples
In the following example, the DHCP server will use the subscriber identifier as the client identifier for all incoming messages received on Ethernet interface 0/0:
interface Ethernet0/0ip dhcp server use subscriber-id client-idRelated Commands
ip dhcp use subscriber-id client-id
Configures the DHCP server to globally use the subscriber identifier as the client identifier on all incoming DHCP messages.
ip dhcp smart-relay
To allow the Cisco IOS Dynamic Host Configuration Protocol (DHCP) relay agent to switch the gateway address (giaddr field of a DHCP packet) to secondary addresses when there is no DHCPOFFER message from a DHCP server, use the ip dhcp smart-relay command in global configuration mode. To disable this smart-relay functionality and restore the default behavior, use the no form of this command.
ip dhcp smart-relay
no ip dhcp smart-relay
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
The DHCP relay agent attempts to forward the primary address as the gateway address three times. After three attempts and no response, the relay agent automatically switches to secondary addresses.
Examples
The following example enables the DHCP relay agent to automatically switch to secondary address pools:
ip dhcp smart-relayip dhcp snooping
To globally enable DHCP snooping, use the ip dhcp snooping command in global configuration mode. To disable DHCP snooping, use the no form of this command.
ip dhcp snooping
no ip dhcp snooping
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Global configuration
Command History
12.2(18)SXE
Support for this command was introduced on the Supervisor Engine 720.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
Usage Guidelines
Wireless clients, or mobile nodes, gain access to an untrusted wireless network only if there is a corresponding entry in the DHCP snooping database. Enable DHCP snooping globally by entering the ip dhcp snooping command, and enable DHCP snooping on the tunnel interface by entering the ip dhcp snooping packets command. After you enable DHCP snooping, the process snoops DHCP packets to and from the mobile nodes and populates the DHCP snooping database.
Examples
This example shows how to enable DHCP snooping:
Router(config) # ip dhcp snoopingThis example shows how to disable DHCP snooping:
Router(config) # no ip dhcp snoopingRelated Commands
ip dhcp snooping binding
To set up and generate a DHCP binding configuration to restore bindings across reboots, use the ip dhcp snooping binding command in privileged EXEC mode. To disable the binding configuration, use the no form of this command.
ip dhcp snooping binding mac-address vlan vlan ip-address interface type number expiry seconds
no ip dhcp snooping binding mac-address vlan vlan ip-address interface type number
Syntax Description
Defaults
This command has no default settings.
Command Modes
Privileged EXEC
Command History
12.2(18)SXE
Support for this command was introduced on the Supervisor Engine 720.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
Usage Guidelines
When you add or remove a binding using this command, the binding database is marked as changed and a write is initiated.
Examples
This example shows how to generate a DHCP binding configuration on interface gigabitethernet1/1 in VLAN 1 with an expiration time of 1000 seconds:
Router# ip dhcp snooping binding 0001.1234.1234 vlan 1 172.20.50.5 interface gi1/1 expiry 1000Related Commands
ip dhcp snooping database
To configure the Dynamic Host Configuration Protocol (DHCP)-snooping database, use the ip dhcp snooping database command in global configuration mode. To disable the DHCP-snooping database, use the no form of this command.
ip dhcp snooping database {bootflash:url | ftp:url | rcp:url | scp:url | sup-bootflash: | tftp:url | timeout seconds | write-delay seconds}
no ip dhcp snooping database {timeout seconds | write-delay seconds}
Syntax Description
Defaults
The DHCP-snooping database is not configured.
Command Modes
Global configuration
Command History
Usage Guidelines
You must enable DHCP snooping on the interface before entering this command. Use the ip dhcp snooping command to enable DHCP snooping.
Examples
This example shows how to specify the database URL using TFTP:
Router(config)# ip dhcp snooping database tftp://10.90.90.90/snooping-rp2This example shows how to specify the amount of time before writing DHCP snooping entries to an external server:
Router(config)# ip dhcp snooping database write-delay 15Related Commands
ip dhcp snooping information option
To enable Dynamic Host Configuration Protocol (DHCP) option 82 data insertion, use the ip dhcp snooping information option command in global configuration mode. To disable DHCP option 82 data insertion, use the no form of this command.
ip dhcp snooping information option [allow-untrusted]
no ip dhcp snooping information option
Syntax Description
allow-untrusted
(Optional) Enables the switch to accept incoming DHCP snooping packets with option 82 information from the edge switch.
Defaults
DHCP option 82 data insertion is enabled by default. Accepting incoming DHCP snooping packets with option 82 information from the edge switch is disabled by default.
Command Modes
Global configuration
Command History
Usage Guidelines
DHCP option 82 is part of RFC 3046. DHCP is an application-layer protocol that is used for the dynamic configuration of TCP/IP networks. The protocol allows for a relay agent to pass DHCP messages between the DHCP clients and DHCP servers. By using a relay agent, servers need not be on the same network as the clients. Option 82 (82 is the option's code) addresses the security and scalability issues. Option 82 resides in the relay agent when DHCP packets that originate from the forwarding client are sent to the server. Servers that recognize Option 82 may use the information to implement the IP address or other parameter assignment policies. The DHCP server echoes the option back to the relay agent in its replies. The relay agent strips out the option from the relay agent before forwarding the reply to the client.
When you enter the ip dhcp snooping information option allow-untrusted on an aggregation switch that is connected to an edge switch through an untrusted interface, the aggregation switch accepts packets with option 82 information from the edge switch. The aggregation switch learns the bindings for hosts connected through an untrusted switch interface. You can enable the DHCP security features, such as dynamic Address Resolution Protocol (ARP) inspection or IP source guard, on the aggregation switch while the switch receives packets with option 82 information on untrusted input interfaces to which hosts are connected. You must configure the port on the edge switch that connects to the aggregation switch as a trusted interface.
Caution
Examples
This example shows how to enable DHCP option 82 data insertion:
ip dhcp snooping information optionThis example shows how to disable DHCP option 82 data insertion:
no ip dhcp snooping information optionThis example shows how to enable the switch to accept incoming DHCP snooping packets with option 82 information from the edge switch:
ip dhcp snooping information option allow-trustedRelated Commands
ip dhcp snooping limit rate
To configure the number of the DHCP messages that an interface can receive per second, use the ip dhcp snooping limit rate command in interface configuration mode. To disable the DHCP message rate limiting, use the no form of this command.
ip dhcp snooping limit rate rate
no ip dhcp snooping limit rate
Syntax Description
rate
Number of DHCP messages that a switch can receive per second; valid values are from 1 to 4294967294 seconds.
Defaults
Disabled
Command Modes
Interface configuration
Command History
12.2(18)SXE
Support for this command was introduced on the Supervisor Engine 720.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
Usage Guidelines
This command is supported on Layer 2 switch-port and port-channel interfaces only.
Typically, the rate limit applies to the untrusted interfaces. If you want to set up rate limiting for the trusted interfaces, note that the trusted interfaces aggregate all DHCP traffic in the switch, and you will need to adjust the rate limit of the interfaces to a higher value.
Examples
This example shows how to specify the number of DHCP messages that a switch can receive per second:
Router(config-if)# ip dhcp snooping limit rate 150This example shows how to disable the DHCP message rate limiting:
Router(config-if)# no ip dhcp snooping limit rateRelated Commands
ip dhcp snooping packets
To enable DHCP snooping on the tunnel interface, use the ip dhcp snooping packets command in interface configuration mode. To disable DHCP snooping, use the no form of this command.
ip dhcp snooping packets
no ip dhcp snooping packets
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
12.2(18)SXE
Support for this command was introduced on the Supervisor Engine 720.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
Usage Guidelines
This command is supported on Layer 2 switch-port and port-channel interfaces only.
This command is supported on Cisco 7600 series routers that are configured with a WLSM only.
Wireless clients, or mobile nodes, gain access to an untrusted wireless network only if there is a corresponding entry in the DHCP snooping database. Enable DHCP snooping globally by entering the ip dhcp snooping command, and enable DHCP snooping on the tunnel interface by entering the ip dhcp snooping packets command. After you enable DHCP snooping, the process snoops DHCP packets to and from the mobile nodes and populates the DHCP snooping database.
Examples
This example shows how to enable DHCP snooping:
Router(config-if)# ip dhcp snooping packetsThis example shows how to disable DHCP snooping:
Router(config-if)# no ip dhcp snooping packetsRelated Commands
ip dhcp snooping verify mac-address
To verify that the source MAC address in a DHCP packet matches the client hardware address on an untrusted port, use the ip dhcp snooping verify mac-address command in global configuration mode. To disable verification, use the no form of this command.
ip dhcp snooping verify mac-address
no ip dhcp snooping verify mac-address
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Global configuration
Command History
12.2(18)SXE
Support for this command was introduced on the Supervisor Engine 720.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
Usage Guidelines
For untrusted DHCP snooping ports, DHCP snooping verifies the MAC address on the client hardware address field to ensure that a client is requesting multiple addresses from a single MAC address. You can use the ip dhcp snooping verify mac-address command to trust the ports or you can use the no ip dhcp snooping verify mac-address command to leave the ports untrusted by disabling the MAC address verification on the client hardware address field.
Examples
This example shows how to verify that the source MAC address in a DHCP packet matches the client hardware address on an untrusted port:
Router(config)# ip dhcp snooping verify mac-addressThis example shows how to turn off the verification of the MAC address on the client hardware address field:
Router(config)# no ip dhcp snooping verify mac-addressRelated Commands
ip dhcp snooping vlan
To enable DHCP snooping on a VLAN or a group of VLANs, use the ip dhcp snooping vlan command in global configuration mode. To disable DHCP snooping on a VLAN or a group of VLANs, use the no form of this command.
ip dhcp snooping vlan {number | vlan-list}
no ip dhcp snooping vlan {number | vlan-list}
Syntax Description
number | vlan-list
VLAN number or a group of VLANs; valid values are from 1 to 4094. See the "Usage Guidelines" section for additional information.
Defaults
Disabled
Command Modes
Global configuration
Command History
12.2(18)SXE
Support for this command was introduced on the Supervisor Engine 720.
12.2(33)SRA
This command was integrated into Cisco IOS Release 12.2(33)SRA.
Usage Guidelines
DHCP snooping is enabled on a VLAN only if both the global snooping and the VLAN snooping are enabled.
Enter the range of VLANs using this format: 1,3-5,7,9-11.
Examples
This example shows how to enable DHCP snooping on a VLAN:
Router(config)# ip dhcp snooping vlan 10This example shows how to disable DHCP snooping on a VLAN:
Router(config)# no ip dhcp snooping vlan 10This example shows how to enable DHCP snooping on a group of VLANs:
Router(config)# ip dhcp snooping vlan 10,4-8,55This example shows how to disable DHCP snooping on a group of VLANs:
Router(config)# no ip dhcp snooping vlan 10,4-8,55Related Commands
ip dhcp subscriber-id interface-name
To automatically generate a subscriber ID value based on the short name of the interface, use the ip dhcp subscriber-id interface-name command in global configuration mode. To disable this functionality, use the no form of this command.
ip dhcp subscriber-id interface-name
no ip dhcp subscriber-id interface-name
Syntax Description
This command has no arguments or keywords.
Command Default
A subscriber ID value is not automatically generated.
Command Modes
Global configuration (config)
Command History
Usage Guidelines
A subscriber ID value configured on a specific interface using the ip dhcp server use subscriber-id client-id command takes precedence over the global configuration.
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
ip dhcp server use subscriber-id client-id
Configures the DHCP server to use the subscriber identifier as the client identifier on all incoming DHCP messages on an interface.
ip dhcp use class
To control whether the DHCP server uses DHCP classes during address allocation, use the ip dhcp use class command in global configuration mode. To disable the use of DHCP classes during address allocation, use the no form of this command.
ip dhcp use class
no ip dhcp use class
Syntax Description
This command has no arguments or keywords.
Defaults
This command is enabled by default.
Command Modes
Global configuration
Command History
Usage Guidelines
When you use the no ip dhcp use class command, the DHCP class configuration is not deleted.
Examples
The following example shows the DHCP server configured to use the relay agent information option during address allocation:
ip dhcp use classip dhcp use subscriber-id client-id
To configure the DHCP server to globally use the subscriber identifier as the client identifier on all incoming DHCP messages, use the ip dhcp use subscriber-id client-id command in global configuration mode. To disable this functionality, use the no form of this command.
ip dhcp use subscriber-id client-id
no ip dhcp use subscriber-id client-id
Syntax Description
This command has no arguments or keywords.
Command Default
DHCP uses the client identifier option in the DHCP packet to identify clients.
Command Modes
Global configuration (config)
Command History
Usage Guidelines
A subscriber ID value configured on a specific interface using the ip dhcp server use subscriber-id client-id command takes precedence over this command.
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
ip dhcp server use subscriber-id client-id
Configures the DHCP server to use the subscriber identifier as the client identifier on all incoming DHCP messages on an interface.
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 command in DHCP pool configuration mode. To restore the default value, use the no form of this command.
lease {days [hours [minutes]] | infinite}
no lease
Syntax Description
Defaults
1 day
Command Modes
DHCP pool configuration
Command History
Examples
The following example shows a 1-day lease:
lease 1The following example shows a 1-hour lease:
lease 0 1The following example shows a 1-minute lease:
lease 0 0 1The following example shows an infinite (unlimited) lease:
lease infiniteRelated Commands
ip dhcp pool
Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode.
