Cisco IOS IP Addressing Services Command Reference

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


`server-group-name`	Name of a server group to apply DHCP accounting. The server group can have one or more members. The server group is defined in the configuration of the aaa group server and aaa accounting commands.

Command Default

DHCP accounting is not enabled by default.

Command Modes

DHCP pool configuration (dhcp-config)

Command History


Release	Modification
12.2(15)T	This command was introduced.
12.2(28)SB	This command was integrated into Cisco IOS Release 12.2(28)SB.
15.0(1)S	This command was integrated into Cisco IOS Release 15.0(1)S.

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 only 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.

Authentication, authorization, and accounting (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 shows how to configure DHCP accounting start and stop messages to be sent if RADIUS-GROUP1 is configured as a start-stop group. Stop messages will be sent only if RADIUS-GROUP1 is configured as a stop-only group.


Router(config)# ip dhcp pool pool1
 
Router(dhcp-config)# accounting group1

Related Commands


Command	Description
aaa accounting	Enables AAA accounting of requested services for billing or security purposes when you use RADIUS or TACACS+.
aaa group serve r	Groups different server hosts into distinct lists and distinct methods.
aaa new-model	Enables the AAA access control model.
aaa session-id	Specifies whether the same session ID will be used for each AAA accounting service type within a call or whether a different session ID will be assigned to each accounting service type.
clear arp-cache	Deletes all dynamic entries from the ARP cache.
clear ip dhcp binding	Deletes an automatic address binding from the Cisco IOS DHCP server database.
ip dhcp pool	Configures a DHCP address pool on a Cisco IOS DHCP server and enters DHCP pool configuration mode.
ip radius source-interface	Forces RADIUS to use the IP address of a specified interface for all outgoing RADIUS packets.
radius-server hos t	Specifies a RADIUS server host.
radius-server retransmit	Specifies the number of times that Cisco IOS will look for RADIUS server hosts.
service dhcp	Enables the Cisco IOS DHCP server and relay agent features.
show ip dhcp binding	Displays address bindings on the Cisco IOS DHCP server.
show ip dhcp server statistics	Displays Cisco IOS DHCP server statistics.
update arp	Secures the MAC address of the authorized client interface to the DHCP binding.

accounting (DHCP for IPv6)

To enable sending of accounting start and stop messages, use the accounting command in DHCP for IPv6 pool configuration mode. To remove configuration for these messages, use the no form of this command.

accounting mlist

no accounting mlist

Syntax Description


`mlist`	Accounting list to which start and stop messages are sent.

Command Default

Accounting start and stop messages are not configured.

Command Modes

DHCP for IPv6 pool configuration (config-dhcp)

Command History


Release	Modification
Cisco IOS Release XE 2.5	This command was introduced.
12.2(50)SY	This command was integrated into Cisco IOS Release 12.2(50)SY.

Usage Guidelines

The accounting command allows users to configure and send accounting start and stop messages to a named accounting list. When accounting is configured for a DHCPv6 pool, accounting interim packets are sent to broadband sessions after binding is provided from the pool.

Examples

The following example configures accounting start and stop messages to be sent to an accounting list called list1:


Router(config)# ipv6 dhcp pool pool1
Router(config-dhcp)# accounting list1

address client-id

To reserve an IP address for a Dynamic Host Configuration Protocol (DHCP) client identified by a 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

Syntax Description


`ip-address`	IP address reserved for the client.
`string`	A unique ASCII string or hexadecimal string.
ascii	(Optional) Specifies that the client ID is in ASCII string form.

Command Default

IP addresses are not reserved.

Command Modes

DCHP pool configuration (dhcp-config)

Command History


Release	Modification
12.2(46)SE	This command was introduced.
12.2(33)SXI4	This command was integrated into Cisco IOS Release 12.2(33)SXI4.

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.


Router(config)# ip dhcp use subscriber-id client-id
Router(config)# ip dhcp subscriber-id interface-name
Router(config)# ip dhcp excluded-address 10.1.1.1 10.1.1.3
Router(config)# ip dhcp pool dhcppool
Router(dhcp-config)# network 10.1.1.0 255.255.255.0
Router(dhcp-config)# address 10.1.1.7 client-id ethernet 1/0 ascii

Related Commands


Command	Description
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

Syntax Description


`ip-address`	IP address reserved for the client.
`mac-address`	Hardware address of the client.
`hardware-number`	(Optional) Address Resolution Protocol (ARP) hardware specified in an online database at http://www.iana.org/assignments/arp-parameters. The range is from 0 to 255.

Command Default

IP addresses are not reserved.

Command Modes

DHCP pool configuration (dhcp-config)

Command History


Release	Modification
12.2(46)SE	This command was introduced.
12.2(33)SXI4	This command was integrated into Cisco IOS Release 12.2(33)SXI4.

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 Dynamic Host Configuration Protocol (DHCP) message.

Examples

In the following example, an IP address is reserved for a client that is identified by its hardware address:


Router(config)# ip dhcp pool dhcppool
Router(dhcp-config)# address 10.10.10.3 hardware-address b708.1388.f166

Related Commands


Command	Description
address client-id	Reserves an IP address for a DHCP client identified by the client identifier.

address prefix

To specify an address prefix for address assignment, use the address prefix command in interface configuration mode. To remove the address prefix, use the no form of this command.

address prefix ipv6-prefix [lifetime {valid-lifetime preferred-lifetime | infinite}]

no address prefix

Syntax Description


`ipv6-prefix`	IPv6 address prefix.
lifetime {valid-lifetime preferred-lifetime \| infinite}]	(Optional) Specifies a time interval (in seconds) that an IPv6 address prefix remains in the valid state. If the infinite keyword is specified, the time interval does not expire.

Command Default

No IPv6 address prefix is assigned.

Command Modes

DHCP pool configuration (config-dhcpv6)

Command History


Release	Modification
12.4(24)T	This command was introduced.

Usage Guidelines

You can use the address prefix command to configure one or several address prefixes in an IPv6 DHCP pool configuration. Each time the IPv6 DHCP address pool is used, an address will be allocated from each of the address prefixes associated with the IPv6 DHCP pool.

Examples

The following example shows how to configure a pool called engineering with an IPv6 address prefix:


Router(config)# ipv6 dhcp pool engineering
Router(config-dhcpv6)# address prefix 2001:1000::0/64 lifetime infinite

Related Commands


Command	Description
ipv6 dhcp pool	Configures a DHCPv6 server configuration information pool and enters DHCPv6 pool configuration mode.

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.

Command Default

No DHCP address range is set.

Command Modes

DHCP pool class configuration (config-dhcp-pool-class)

Command History


Release	Modification
12.2(13)ZH	This command was introduced.
12.3(4)T	This command was integrated into Cisco IOS Release 12.3(4)T.
12.2(28)SB	This command was integrated into Cisco IOS Release 12.2(28)SB.
12.2(33)SRB	This command was integrated into Cisco IOS Release 12.2(33)SRB.
15.0(1)S	This command was integrated into Cisco IOS Release 15.0(1)S.

Usage Guidelines

If the address range 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 shows how to set the available address range for class 1 from 10.0.20.1 through 10.0.20.100:


Router(config)# ip dhcp pool pool1
Router(dhcp-config)# network 10.0.20.0 255.255.255.0
Router(dhcp-config)# class class1
Router(config-dhcp-pool-class)# address range 10.0.20.1 10.0.20.100

Related Commands


Command	Description
ip dhcp class	Defines a DHCP class and enters DHCP class configuration mode.

application redundancy

To enter redundancy application configuration mode, use the application redundancy command in redundancy configuration mode.

application redundancy

Syntax Description

This command has no arguments or keywords.

Command Default

None

Command Modes

Redundancy configuration (config-red)

Command History


Release	Modification
Cisco IOS XE Release 3.1S	This command was introduced.

Examples

The following example shows how to enter redundancy application configuration mode:


Router# configure terminal
Router(config)# redundancy
Router(config-red)# application redundancy
Router(config-red-app)#

Related Commands


Command	Description
group (firewall)	Enters redundancy application group configuration mode.

alg sip blacklist

To configure a dynamic Session Initiation Protocol (SIP) application layer gateway (ALG) blocked list for destinations, use the alg sip blacklist command in global configuration mode. To remove a blocked list, use the no form of this command.

alg sip blacklist trigger-period seconds trigger-size number-of-events [block-time block-time] [destination ipv4-address]

no alg sip blacklist trigger-period seconds trigger-size number-of-events [block-time block-time] [destination ipv4-address]

Syntax Description


trigger-period `seconds`	Specifies the time period, in seconds, during which events are monitored before a blocked list is triggered. Valid values are from 10 to 60000.
trigger-size `number-of-events`	Specifies the number of events that are allowed from a source before the blocked list is triggered and all packets from that source are blocked. Valid values are from 1 to 65535.
block-time `block-time`	(Optional) Specifies the time period, in seconds, when packets from a source are blocked if the configured limit is exceeded. Valid values are from 0 to 2000000. The default is 30.
destination `ipv4-address`	(Optional) Specifies the destination IP address to be monitored.

Command Default

A blocked list is not configured.

Command Modes

Global configuration (config)

Command History


Release	Modification
Cisco IOS XE Release 3.11S	This command was introduced.

Usage Guidelines

If the configured block time is zero, it means that a blocked list is not configured for the source. If no destination is specified, all destinations are monitored for denial of service (DoS) attacks.

The following events trigger a blocked list:

In the configured period of time if a source sends multiple requests to a destination and receives non-2xx (as per RFC 3261, any response with a status code between 200 and 299 is a "2xx response") final responses from the destination.
In the configured period of time if a source sends multiple requests to a destination and does not receive any response from the destination.

Examples

The following example shows how to configure a blocked list for the destination IP address 10.2.2.23:

Device(config)# alg sip blacklist trigger-period 100 trigger-size 10 destination 10.2.2.23

Related Commands


show alg sip	Displays all SIP ALG information.

alg sip processor

To configure the maximum number of backlog messages that wait for shared processor resources, use the alg sip processor command in global configuration mode. To disable the configuration, use the no form of this command.

alg sip processor {global | session} max-backlog concurrent-usage

no alg sip processor {global | session} max-backlog concurrent-usage

Syntax Description


global	Sets the maximum number of backlog messages that are waiting for shared resources for all Session Initiation Protocol (SIP) sessions. The default is 100.
session	Sets a per session limit for the number of backlog messages waiting for shared resources. The default is 10.
max-backlog	Specifies the maximum backlog for all sessions or for a single session.
`concurrent-usage`	Maximum number of backlog messages waiting for concurrent processor usage. Valid values are from 1 to 200 for the global keyword and from 1 to 20 for the session keyword.

Command Default

Blocked list messages are enabled.

Command Modes

Global configuration (config)

Command History


Release	Modification
Cisco IOS XE Release 3.11S	This command was introduced.

Usage Guidelines

Use this command to configure parameters against distributed denial of service (DoS) attacks.

Examples

The following example shows set the per session limit for the number of backlog messages:

Device(config)# alg sip processor session max-backlog 5

Related Commands


show alg sip	Displays all SIP ALG information.

alg sip timer

To configure a timer that the Session Initiation Protocol (SIP) application layer gateway (ALG) uses to manage SIP calls, use the alg sip timer command in global configuration mode. To remove the configured timer, use the no form of this command.

alg sip timer {call-proceeding-timeout call-proceeding-time | max-call-duration call-duration}

no alg sip timer {call-proceeding-timeout call-proceeding-time | max-call-duration call-duration}

Syntax Description


call-proceeding-timeout `call-proceeding-time`	Sets the call proceeding time interval, in seconds, for SIP calls that do not receive a response. The range is from 30 to 1800. The default is 180.
max-call-duration `call-duration`	Sets the maximum call duration, in seconds, for a successful SIP call. The range is from 0 to 65535. The default is 3600.

Command Default

A timer is not configured for SIP ALG calls.

Command Modes

Global configuration (config)

Command History


Release	Modification
Cisco IOS XE Release 3.11S	This command was introduced.

Usage Guidelines

The timer that you configure with the alg sip timer call-proceeding-timeout command is similar to the number of times a phone rings for a call; the SIP ALG releases the SIP call if the call is not connected after the final ring.

When you configure the alg sip timer max-call-duration command, all SIP calls whose duration exceeds the configured value is released. The SIP ALG only releases resources that are used by the calls; and the SIP ALG is not torn down.

Examples

The following example shows how to configure a maximum time interval after which an unsuccessful SIP call is released:

Device(config)# alg sip timer call-proceeding-timeout 200

The following example shows how to configure a call duration time for a successful SIP call:

Device(config)# alg sip timer max-call-duration 180

Related Commands


show alg sip	Displays all SIP ALG information.

arp (global)

To add a permanent entry in the Address Resolution Protocol (ARP) cache, use the arp command in global configuration mode. To remove an entry from the ARP cache, use the no form of this command.

arp {ip-address | vrf vrf-name} hardware-address encap-type [interface-type] [alias]

no arp {ip-address | vrf vrf-name} hardware-address encap-type [interface-type] [alias]

Cisco IOS 12.2(33)SXI Release and Later Releases

arp {ip-address | vrf vrf-name | access-list name | clear retry count} hardware-address encap-type [interface-type] [alias]

no arp {ip-address | vrf vrf-name | access-list name | clear retry count} hardware-address encap-type [interface-type] [alias]

Syntax Description


`ip-address`	IP address in four-part dotted decimal format corresponding to the local data-link address.
vrf `vrf-name`	Virtual routing and forwarding (VRF) instance. The `vrf-name` argument is the name of the VRF table.
access-list	Specifies the named access-list.
`name`	Access-list name.
clear	Clears ARP command parameter.
retry	Specifies the number of retries.
`count`	Retry attempts. The range is from 1 to 50.
`hardware-address`	Local data-link address (a 48-bit address).
`encap-type`	Encapsulation description. The keywords are as follows: arpa --For Ethernet interfaces. sap --For Hewlett Packard interfaces. smds --For Switched Multimegabit Data Service (SMDS) interfaces. snap --For FDDI and Token Ring interfaces. srp-a --Switch Route Processor, side A (SRP-A) interfaces. srp-b --Switch Route Processor, side B (SRP-B) interfaces.
`interface-type`	(Optional) Interface type. For more information, use the question mark (?) online help. The keywords are as follows: ethernet --IEEE 802.3 interface. loopback --Loopback interface. null --No interface. serial --Serial interface.
alias	Responds to ARP requests for the IP address.

Command Default

No entries are permanently installed in the ARP cache.

Command Modes

Global configuration (config)

Command History


Release	Modification
10.0	This command was introduced.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Cisco IOS XE Release 2.1	This command was integrated into Cisco IOS XE Release 2.1.
12.2(33)SXI	This command was modified in a release earlier than Cisco IOS Release 12.2(33)SXI. The clear and retry keywords were added. The `count` argument was added.
Cisco IOS XE Release 3.9S	This command was integrated into Cisco IOS XE Release 3.9S

Usage Guidelines

The Cisco IOS software uses ARP cache entries to translate 32-bit IP addresses into 48-bit hardware addresses.

Because most hosts support dynamic resolution, you generally need not specify static ARP cache entries.

To remove all nonstatic entries from the ARP cache, use the clear arp-cache privileged EXEC command.

Examples

The following is an example of a static ARP entry for a typical Ethernet host:


arp 10.31.7.19 0800.0900.1834 arpa

Related Commands


Command	Description
clear arp-cache	Deletes all dynamic entries from the ARP cache.

arp (interface)

To support a type of encapsulation for a specific network, such as Ethernet, Fiber Distributed Data Interface (FDDI), Frame Relay, and Token Ring, so that the 48-bit Media Access Control (MAC) address can be matched to a corresponding 32-bit IP address for address resolution, use the arp command in interface configuration mode. To disable an encapsulation type, use the no form of this command.

arp {arpa | frame-relay | snap}

no arp {arpa | frame-relay | snap}

Syntax Description


arpa	Standard Ethernet-style Address Resolution Protocol (ARP) ( RFC 826).
frame-relay	Enables ARP over a Frame Relay encapsulated interface.
snap	ARP packets conforming to RFC 1042.

Command Default

Standard Ethernet-style ARP

Command Modes

Interface configuration

Command History


Release	Modification
10.0	This command was introduced.
12.2(13)T	The probe keyword was removed because the HP Probe feature is no longer available in Cisco IOS software.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
12.0(33)S	Support for IPv6 was added. This command was implemented on the Cisco 12000 series routers.

Usage Guidelines

Unlike most commands that have multiple arguments, the arp command has arguments that are not mutually exclusive. Each command enables or disables a specific type of encapsulation.

Given a network protocol address (IP address), the arp frame-relay command determines the corresponding hardware address, which would be a data-link connection identifier (DLCI) for Frame Relay.

The show interfaces command displays the type of encapsulation being used on a particular interface. To remove all nonstatic entries from the ARP cache, use the clear arp-cache command.

Examples

The following example enables Frame Relay services:


interface ethernet 0
 arp frame-relay

Related Commands


Command	Description
clear arp-cache	Deletes all dynamic entries from the ARP cache.
show interfaces	Displays statistics for all interfaces configured on the router or access server.

arp access-list

To configure an Address Resolution Protocol access control list (ARP ACL) for ARP inspection and QoS filtering and enter the ARP ACL configuration submode, use the arp access-list command in global configuration mode. To remove the ARP ACL, use the no form of this command.

arp access-list name

no arp access-list name

Syntax Description


`name`	Name of the access list.

Command Default

This command has no default settings.

Command Modes

Global configuration

Command History


Release	Modification
12.2(18)SXD	Support for this command was introduced on the Supervisor Engine 720.
12.2(18)SXE	This command was changed to support DAI on the Supervisor Engine 720. See the “Usage Guidelines” section for the syntax description.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.

Usage Guidelines

Once you are in the ARP ACL configuration submode, you can add permit or deny clauses to permit or deny QoS to the flows. The following syntax is available in the ARP QoS ACL configuration submode for QoS filtering; all other configurations will be rejected at the time of the policy-map attachment to the interfaces:

{permit | deny} ip {any | host sender-ip [sender-ip-mask] } mac any

no {permit | deny} ip {any | host sender-ip [sender-ip-mask] } mac any


permit	Specifies to apply QoS to the flows.
deny	Skips the QoS action that is configured for traffic matching this ACE.
ip	Specifies the IP ARP packets.
any	Specifies any IP ARP packets.
host `sender-ip`	Specifies the IP address of the host sender.
`sender-ip-mask`	(Optional) Subnet mask of the host sender.
mac any	Specifies MAC-layer ARP traffic.
no	Deletes an ACE from an ARP ACL.

Once you are in the ARP ACL configuration submode, the following configuration commands are available for ARP inspection:

default --Sets a command to its defaults. You can use the deny and permit keywords and arguments to configure the default settings.
deny --Specifies the packets to reject.
exit --Exits the ACL configuration mode.
no --Negates a command or set its defaults.
permit -- Specifies the packets to forward.

You can enter the permit or deny keywords to configure the permit or deny clauses to forward or drop ARP packets based on some matching criteria. The syntax for the permit and deny keywords are as follows:

{permit | deny} ip {any | host sender-ip [sender-ip sender-ip-mask]} mac {any | host sender-mac [sender-mac-mask] } [log]

{permit | deny} request ip {any | host sender-ip [sender-ip-mask]} mac {any | host sender-mac [sender-mac-mask]} [log]

{permit | deny} response ip {any | host sender-ip [sender-ip-mask]} [any | host target-ip [target-ip-mask]] mac {any | host sender-mac [sender-mac-mask]} [any | host target-mac [target-mac-mask]] [log]


permit	Specifies packets to forward.
deny	Specifies packets to reject.
ip	Specifies the sender IP address.
any	Specifies any sender IP address.
host	Specifies a single sender host.
`sender-ip`	IP address of the host sender.
`sender-ip-mask`	Subnet mask of the host sender.
mac any	Specifies any MAC address.
mac host	Specifies a single sender host MAC address.
`sender-mac`	MAC address of the host sender.
`sender-mac-mask`	Subnet mask of the host sender.
log	(Optional) Specifies log on match.
request	Specifies ARP requests.
response	Specifies ARP responses.
any	(Optional) Specifies any target address.
host	(Optional) Specifies a single target host.
`target-ip`	IP address of the target host.
`target-ip-mask`	Subnet mask of the target host.
`target-mac`	MAC address of the target host.
`target-mac-mask`	Subnet mask of the target host.

If you enter the ip keyword without the request or response keywords, the configuration applies to both requests and responses.

Once you define an ARP ACL, you can apply it to VLANs using the ip arp inspection filter command for ARP inspection.

Incoming ARP packets are compared against the ARP access list, and packets are permitted only if the access list permits them. If access lists deny packets because of explicit denies, they are dropped. If packets get denied because of the implicit deny, they are matched against the list of DHCP bindings, unless the access list is static or the packets are not compared against the bindings.

When a ARP access list is applied to a VLAN for dynamic ARP inspection, the ARP packets containing only IP-to-Ethernet MAC bindings are compared against the ACLs. All other type of packets are bridged in the incoming VLAN without any validation.

ACL entries are scanned in the order that you enter them. The first matching entry is used. To improve performance, place the most commonly used entries near the beginning of the ACL.

An implicit deny ip any mac any entry exists at the end of an ACL unless you include an explicit permit ip any mac any entry at the end of the list.

All new entries to an existing list are placed at the end of the list. You cannot add entries to the middle of a list.

Examples

This example shows how to create a new ARP ACL or enter the submode of an existing ARP ACL:


Router(config)# arp access-list arpacl22
Router(config-arp-nacl)#

This example shows how to create an ARP ACL named arp_filtering that denies QoS but permits MAC-layer ARP traffic:


Router(config)# arp access-list arp_filtering
 
Router(config-arp-nacl)# permit ip host 10.1.1.1 mac any
Router(config-arp-nacl)# deny ip any mac any 
Router(config-arp-nacl)#

Related Commands


Command	Description
show arp	Displays information about the ARP table.

arp authorized

To disable dynamic Address Resolution Protocol (ARP) learning on an interface, use the arp authorized command in interface configuration mode. To reenable dynamic ARP learning, use the no form of this command.

arp authorized

no arp authorized

Syntax Description

This command has no arguments or keywords.

Command Default

No default behavior or values

Command Modes

Interface configuration

Command History


Release	Modification
12.3(4)T	This command was introduced.

Usage Guidelines

The arp authorized command disables dynamic ARP learning on an interface. This command enhances security in public wireless LANs (PWLANs) by limiting the leasing of IP addresses to mobile users and authorized users. The mapping of IP address to MAC address for an interface can be installed only by the authorized subsystem. Unauthorized clients cannot respond to ARP requests.

If both static and authorized ARP are installing the same ARP entry, the static configuration overrides the authorized ARP entry. To install a static ARP entry use the arp (global) command. A nondynamic ARP entry can only be removed by using the same method by which it was installed.

The arp authorized command can only be specified on Ethernet interfaces and for Dynamic Host Configuration Protocol (DHCP) networks.

Examples

The following example disables dynamic ARP learning on interface Ethernet 0:


interface Ethernet0
 ip address 10.0.0.1 255.255.255.0
 arp authorized

Related Commands


Command	Description
arp (global)	Adds a permanent entry in the ARP cache.
update arp	Secures dynamic ARP entries in the ARP table to their corresponding DHCP bindings.

arp log threshold entries

To enable an Address Resolution Protocol (ARP) trap so that the ARP log is triggered when a specific number of dynamically learned entries is reached on the router interface, use the arp log threshold entries command in interface configuration mode. To disable the ARP trap for the interface, use the no form of this command.

arp log threshold entries entry-count

no arp log threshold entries

Syntax Description


`entry-count`	Triggers the ARP log service when the number of dynamically learned entries on the interface reaches this threshold. The range is from 1 to 2147483647.

Command Default

ARP trap is disabled for the interface.

Command Modes

Interface configuration

Command History


Release	Modification
12.4(11)T	This command was introduced.
12.2(31)SB2	This command was integrated into Cisco IOS Release 12.2(31)SB2.
12.2(33)SRB	This command was integrated into Cisco IOS Release 12.2(33)SRB.

Usage Guidelines

This command enables an ARP trap for the router interface. When the number of dynamically learned entries on the interface exceeds the preconfigured amount, an ARP event message is written to system message logging (syslog) output.

A high number of learned entries on the interface might indicate anomalies such as an attempt to breach security through an ARP attack on the router. The threshold at which to configure the ARP log service trigger should be determined heuristically, based on the expected number of nodes the router will serve and the number of hosts on the interface.

To display information about the setting configured by the arp log threshold entries command, use the show running-config command. If an ARP trap is enabled for a given interface, the information for that interface command includes the arp log threshold entries command, followed by the threshold value.

To display the syslog history statistics and buffer contents, use the show logging command.

Examples

The following example shows how to enable an ARP trap so that the ARP log is triggered when 50 dynamically learned entries is reached on the Ethernet interface at slot 2, port 1:


Router(config)# interface ethernet2/1
 
Router(config-if)# arp log threshold entries 50

The following sample output from the show logging command shows that the ARP trap entry was triggered when 50 dynamic ARP entries was reached on the Ethernet interface at slot 2, port 1:


Router# show logging
 
Syslog logging: enabled (0 messages dropped, 39 messages rate-limited, 0 flushes, 0 overruns, xml disabled, filtering disabled)
    Console logging: disabled
    Monitor logging: level debugging, 0 messages logged, xml disabled,
                     filtering disabled
    Buffer logging: level debugging, 309 messages logged, xml disabled,
                    filtering disabled
    Exception Logging: size (8192 bytes)
    Count and timestamp logging messages: disabled
    Persistent logging: disabled
No active filter modules.
    Trap logging: level informational, 312 message lines logged
Log Buffer (65536 bytes):
Jan 27 18:27:32.000: %SYS-6-CLOCKUPDATE: System clock has been updated from 10:27:31 PST Fri Jan 27 2006 to 10:27:32 PST Fri Jan 27 2006, configured from console by console.
Jan 27 18:27:32.431: %SYS-5-CONFIG_I: Configured from console by console
Jan 27 18:27:34.051: %ARP-4-TRAPENTRY: 50 dynamic ARP entries on Ethernet2/1 installed in the ARP table

Related Commands


Command	Description
interface	Selects an interface to configure and enters interface configuration mode.
show logging	Displays the contents of logging buffers.
show running-config	Displays the contents of the currently running configuration file of your routing device.

arp packet-priority enable

To enable Address Resolution Protocol (ARP) packet priority on an interface, use the arp packet-priority enable command in interface configuration mode. To disable ARP packet priority, use the no form of this command.

arp packet-priority enable

no arp packet-priority enable

Syntax Description

This command has no arguments or keywords.

Command Default

By default, ARP packet priority is not enabled.

Command Modes

Interface configuration (config-if)

Command History


Release	Modification
15.1(3)T	This command was introduced.
15.1(1)S	This command was integrated into Cisco IOS Release 15.1(1)S.

Usage Guidelines

Use the arp packet-priority enable command when a network congestion causes ARP packets to drop. Enabling ARP packet priority significantly reduces the number of ARP packet drops.

Before you configure the arp packet-priority enable command, you must configure an IP address for the interface and ensure that the interface is enabled. If the interface is disabled, use the no shutdown command to enable the interface.

Examples

The following example shows how to enable packet priority on a Fast Ethernet interface:


Router(config)# interface FastEthernet0/1
Router(config-if)# no shutdown
Router(config-if)# ip address
 198.51.100.253 255.255.255.0
Router(config-if)# arp packet-priority enable

Related Commands


Command	Description
interface	Configures an interface and enters interface configuration mode.
ip address	Sets a primary or secondary IP address for an interface.
shutdown (interface)	Disables an interface.

arp probe interval

To control the the p robing of authorized peers, use the arp probe interval command in interface configuration mode. To disable the probe, use the no form of this command.

arp probe interval seconds count count-number

no arp probe

Syntax Description


`seconds`	Interval in seconds after which the next probe will be sent to see if the peer is still present. The range is from 1 to 10.
count `count-number`	Number of probe retries. If no response, the peer has logged off. The range is from 1 to 60.

Command Default

Disabled

Command Modes

Interface configuration

Command History


Release	Modification
12.3(8)XX	This command was introduced.
12.3(14)T	This command was integrated into Cisco IOS Release 12.3(14)T.

Usage Guidelines

Once you configure the arp probe interval command, probing continues until you disable it using the no form of the command on all interfaces.

Examples

The following example shows a 2 second interval with a probe of the peer occurring 5 times:


interface ethernet 0
 arp probe interval 2 count 5

Related Commands


Command	Description
arp (interface)	Controls the interface-specific handling of IP address resolution.
clear arp-cache	Deletes all dynamic entries from the ARP cache.
show interfaces	Displays statistics for all interfaces configured on the router or access server.

arp timeout

To configure how long a dynamically learned IP address and its corresponding Media Control Access (MAC) address remain in the Address Resolution Protocol (ARP) cache, use the arp timeout command in interface configuration mode. To restore the default value, use the no form of this command.

arp timeout seconds

no arp timeout

Syntax Description

seconds

Time (in seconds) that an entry remains in the ARP cache.

The general recommended value for ARP timeout is the configured default value, which is 4 hours. If the network has frequent changes to cache entries, change the default to a shorter time period. As you reduce the ARP timeout, your network traffic increases. A low ARP timeout value might lead to network outage, and a value less than an hour (or 3600 seconds) will generate significantly increased traffic across the network.

Caution

We recommend that you set an ARP timeout value greater than 60 seconds.

Command Default

14400 seconds (4 hours)

Command Modes

Interface configuration (config-if)

Command History


Release	Modification
10.0	This command was introduced.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Usage Guidelines

This command is ignored when issued on interfaces that do not use ARP. The show interfaces EXEC command displays the ARP timeout value. The value is displayed in hours, as shown below:


ARP type: ARPA, ARP Timeout 02:00:00

Examples

The following example sets the ARP timeout to 7200 seconds (or 2 hours) to allow entries to time out more quickly than the default:


interface ethernet 0
 arp timeout 7200

Related Commands


Command	Description
show interfaces	Displays statistics for all interfaces configured on the router or access server.

asymmetric-routing

To set up an asymmetric routing link interface and to enable applications to divert packets received on the standby redundancy group to the active, use the asymmetric-routing command in redundancy application group configuration mode. To disable the configuration, use the no form of this command.

asymmetric-routing {always-divert enable | interface type number}

no asymmetric-routing {always-divert enable | interface}

Syntax Description


always-divert enable	Always diverts packets from the standby redundancy group (RG) to the active RG.
interface `type number`	Specifies the asymmetric routing interface that is used by the RG.

Command Default

Asymmetric routing is disabled.

Command Modes

Redundancy application group configuration (config-red-app-grp)

Command History


Release	Modification
Cisco IOS XE Release 3.5S	This command was introduced.
15.2(3)T	This command was integrated into Cisco IOS Release 15.2(3)T.

Usage Guidelines

Asymmetric routing occurs when packets from TCP or UDP connections flow in different directions through different routes. In asymmetric routing, packets that belong to a single connection are forwarded through one router, but return packets of the connection return through another router in the same RG. When you configure the asymmetric routing always-divert enable command, the packets received on the standby RG are redirected to the active RG for processing. If the asymmetric routing always-divert enable command is disabled, the packets received on the standby RG may be dropped.

When you configure the asymmetric-routing interface command, the asymmetric routing feature is enabled. After enabling the feature, configure the asymmetric-routing always-divert enable command to enable Network Address Translation (NAT) to divert packets that are received on the standby RG to the active RG.

Note

The zone-based policy firewall does not support the asymmetric-routing always-divert enable command that diverts packets received on the standby RG to the active RG. The firewall forces all packet flows to be diverted to the active RG.

Examples

The following example shows how to configure asymmetric routing on a Gigabit Ethernet interface:

Router(config)# redundancy
Router(config-red)# application redundancy
Router(config-red-app)# group 2
Router(config-red-app-grp)# asymmetric-routing interface gigabitethernet 0/0/0
Router(config-red-app-grp)# end

Related Commands


Command	Description
application redundancy	Configures application redundancy.
group	Configures a redundancy group.
redundancy	Enters redundancy configuration mode.
redundancy asymmetric-routing enable	Establishes an asymmetric flow diversion tunnel for each redundancy group.

authentication

To configure clear text authentication and MD5 authentication under a redundancy group protocol, use the authentication command in redundancy application protocol configuration mode. To disable the authentication settings in the redundancy group, use the no form of this command.

authentication {text string | md5 key-string [0 | 7] key | md5 key-chain key-chain-name}

no authentication {text string | md5 key-string [0 | 7] key | md5 key-chain key-chain-name}

Syntax Description


text `string`	Uses clear text authentication.
md5 key-string	Uses MD5 key authentication. The `key` argument can be up to 64 characters in length (at least 16 characters is recommended). Specifying 7 means the key will be encrypted.
0	(Optional) Specifies that the text following immediately is not encrypted.
7	(Optional) Specifies that the text is encrypted using a Cisco-defined encryption algorithm.
md5 key-chain `key-chain-name`	Uses MD5 key-chain authentication.

Command Default

The key is not encrypted.

Command Modes

Redundancy application protocol configuration (config-red-app-prtcl)

Command History


Release	Modification
Cisco IOS XE Release 3.1S	This command was introduced.

Examples

The following example shows how to configure clear text authentication for a redundancy group:


Router# configure terminal
Router(config)# redundancy
Router(config-red)# application redundancy
Router(config-red-app)# protocol 1
Router(config-red-app-prtcl)# authentication text name1

Related Commands


Command	Description
application redundancy	Enters redundancy application configuration mode.
group	Enters redundancy application group configuration mode.
name	Configures the redundancy group with a name.
preempt	Enables preemption on the redundancy group.
protocol	Defines a protocol instance in a redundancy group.
timers hellotime	Configures timers for hellotime and holdtime messages for a redundancy group.

authorization method (DHCP)

To specify a method list to be used for address allocation using RADIUS for Dynamic Host Control Protocol (DHCP), use the authorization method command in DHCP pool configuration mode. To disable the authorization method list, use the no form of this command.

authorization method method-list-name

no authorization method method-list-name

Syntax Description


`method-list-name`	An authorization method list of the network type to be used for this DHCP pool.

Command Default

The authorization network default method list is used for authorization.

Command Modes

DHCP pool configuration (config-dhcp)

Command History


Release	Modification
12.2(31)ZV1	This command was modified for the DHCP server RADIUS proxy feature on the Cisco 10000 series router and integrated into Cisco IOS Release 12.2(31)ZV1.
Cisco IOS XE Release 2.4	This command was implemented on the Cisco ASR 1000 Series Aggregation Services Routers.
12.2(33)XNE	This command was integrated into Cisco IOS Release 12.2(33)XNE.
15.0(1)S	This command was integrated into Cisco IOS Release 15.0(1)S.

Usage Guidelines

The method list must be defined during initial authentication setup.

Examples

The following example shows how to set an authorization method of auth1 to download DHCP information from DHCP or a RADIUS server for DHCP clients when pool_common is used:


Router(config)# aaa authorization network auth1 group radius
Router(config)# ip dhcp pool pool_common
Router(config-dhcp)# authorization method auth1

Related Commands


Command	Description
authorization list	Specifies the AAA authorization list.
authorization username (dhcp)	Specifies the parameters that RADIUS sends to a DHCP server when downloading information for a DHCP client.
authorization shared-password	Specifies the password that RADIUS sends to a DHCP or RADIUS server when downloading configuration information for a DHCP client.

authorization shared-password

To specify the password that RADIUS sends to a Dynamic Host Control Protocol (DHCP) or RADIUS server when downloading configuration information for a DHCP client, use the authorization shared-password command in DHCP pool configuration mode. To remove the password used for downloading DHCP client configuration, use the no form of this command.

authorization shared-password password

no authorization shared-password password

Syntax Description


`password`	The password configured in the RADIUS user profile.

Command Default

No password is sent in the RADIUS requests.

Command Modes

DHCP pool configuration (config-dhcp)

Command History


Release	Modification
12.2(31)ZV1	This command was modified for the DHCP server RADIUS proxy feature on the Cisco 10000 series router and integrated into Cisco IOS Release 12.2(31)ZV1.
Cisco IOS XE Release 2.4	This command was implemented on the Cisco ASR 1000 Series Aggregation Services Routers.
12.2(33)XNE	This command was integrated into Cisco IOS Release 12.2(33)XNE.
15.0(1)S	This command was integrated into Cisco IOS Release 15.0(1)S.

Usage Guidelines

This command is used to enter the password that matches the password configured in a RADIUS user profile, at a RADIUS server, for the username matching the string.

Examples

The following example shows how to set the password to cisco:


Router(config)# ip dhcp pool pool_common
Router(config-dhcp)# authorization method auth1
Router(config-dhcp)# authorization shared-password cisco

Related Commands


Command	Description
authorization list	Specifies the AAA authorization list.
authorization method (dhcp)	Specifies the method list to be used for address allocation information.
authorization username (dhcp)	Specifies the parameters that RADIUS sends to a DHCP server when downloading information for a DHCP client.

authorization username (DHCP)

To specify the parameters that RADIUS sends to a Dynamic Host Control Protocol (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

string

A string that RADIUS sends to the DHCP server when downloading an IP address and other configuration information for a client’s DHCP responses.

The string must contain the following formatting characters to insert information associated with the DHCP client:

%% --Transmits the percent sign (%) character in the string sent to the RADIUS server
%c --Ethernet address of the DHCP client (chaddr field) in ASCII format
%C --Ethernet address of the DHCP client in hexadecimal format
%g --Gateway address of the DHCP relay agent (giaddr field)
%i --Inner VLAN ID from the DHCP relay information (option 82) in ASCII format
%I --Inner VLAN ID from the DHCP relay information in hexadecimal format
%o --Outer VLAN ID from the DHCP relay information (option 82) in ASCII format
%O --Outer VLAN ID from the DHCP relay information (option 82) in hexadecimal format
%p --Port number from the DHCP relay information (option 82) in ASCII format
%P --Port number from the DHCP relay information (option 82) in hexadecimal format
%u --Circuit ID from the DHCP relay information in ASCII format
%U --Circuit ID from the DHCP relay information in hexadecimal format
%r --Remote ID from the DHCP relay information in ASCII format
%R --Remote ID from the DHCP relay information in hexadecimal format

Note

The percent (%) is a marker to insert the DHCP client information associated with the specified character. The % is not sent to the RADIUS server unless you specify the %% character.

Command Default

No parameters are specified.

Command Modes

DHCP pool configuration (config-dhcp)

Command History


Release	Modification
12.2(31)ZV1	This command was modified for the DHCP server RADIUS proxy feature on the Cisco 10000 series router and integrated into Cisco IOS Release 12.2(31)ZV1.
Cisco IOS XE Release 2.4	This command was implemented on the Cisco ASR 1000 Series Aggregation Services Routers.
12.2(33)XNE	This command was integrated into Cisco IOS Release 12.2(33)XNE.
15.0(1)S	This command was integrated into Cisco IOS Release 15.0(1)S.

Usage Guidelines

When a DHCP server sends an access request to the authentication, authorization, and accounting (AAA) server, the % and character specified in the username are format characters that is replaced by one of the following values based on the characters specified:

Hardware address
Inner VLAN ID
Outer VLAN ID
Port number
Circuit ID
Remote ID

The % and character specified in the authorization username command configure the DHCP server to send the username in ASCII format or the hexadecimal format based on the case (uppercase or lowercase) of the character used.

For example, if you specify %C with the authorization username command and the hardware address of the client is aabb.ccdd.eeff, then the DHCP server sends the username as “dhcp-AABBCCDDEEFF” in ASCII format. If you specify %c with the authorization username command, then the DHCP server sends the username as “646863702daabbccddeeff” in hexadecimal format. The server sends 11 bytes of data when the format is hexadecimal and 19 bytes when the format is ASCII.

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_common
Router(config-dhcp)# authorization method auth1
Router(config-dhcp)# authorization shared-password cisco 
Router(config-dhcp)# authorization username %c-user1

Related Commands


Command	Description
authorization list	Specifies the AAA authorization list.
authorization method (dhcp)	Specifies the method list to be used for address allocation information.
authorization shared-password	Specifies the password that RADIUS sends to a DHCP or RADIUS server when downloading configuration information for a DHCP client.

auto-ip-ring

To enable the auto-IP functionality on the interfaces of a device, use the auto-ip-ring command in interface configuration mode. To disable the auto-IP functionality, use the no form of this command.

auto-ip-ring ring-id ipv4-address auto-ip-address

no auto-ip-ring ring-id ipv4-address auto-ip-address

Syntax Description

ring-id

Auto-IP ring identification number. The ring ID must be the same for the two network-to-network interfaces (NNIs) of the node.

Note

A device in a ring is called a node.

ipv4-address auto-ip-address

Specifies the auto-IP address configured on a node interface.

Command Default

The auto-IP functionality is not enabled on a node interface.

Command Modes

Interface configuration (config-if)

Command History


Release	Modification
Cisco IOS XE Release 3.10S	This command was introduced.
15.3(3)S	This command was integrated into Cisco IOS Release15.3(3)S

Usage Guidelines

Link Layer Discovery Protocol (LLDP) must be enabled on the device before configuring the auto-IP address on the node interfaces. Use the lldp run command in global configuration mode to enable LLDP.

You must configure the same auto-IP address on both the node interfaces on a device using the auto-ip-ring command. The auto-IP configuration can be enabled on node interfaces in an existing ring or auto-IP configured node interfaces can be inserted into an auto-IP ring.

Note

If you are configuring a seed device, you must use the auto-IP address to configure the IP address on one of the node interfaces, with the mask /31. For example, if 10.1.1.1 is the auto-IP address for the 2 node interfaces, then one of the interfaces must be configured with the IP address 10.1.1.1 255.255.255.254.

Auto-IP addresses should contain an odd number in the last octet (such as 10.1.1.1, where the number in the last octet is 1). When a device is inserted into an auto-IP ring, IP address allocation takes place automatically by subtracting 1 from the last octet of R1’s auto-IP address (10.1.1.0 is allocated to the neighbor node interface).

An auto-IP address must not be configured on an interface which belongs to a Virtual routing and forwarding (VRF) other than the global or default VRF since the auto-IP feature is not supported on a VRF.

Examples

The following example shows how to enable the auto-IP functionality on the interfaces of a device and configure a seed device:

Note

You must configure at least one seed device in an auto-IP ring. In this example, the auto-IP address is being configured on one of the node interfaces with the mask /31 to designate the device as a seed device.


Device> enable
Device# configure terminal
Device(config)# lldp run
Device(config)# interface ethernet 0/0
Device(config-if)# auto-ip-ring 4 ipv4-address 10.1.1.1
Device(config-if)# exit
Device(config)# interface ethernet 1/0
Device(config-if)# auto-ip-ring 4 ipv4-address 10.1.1.1
Device(config-if)# ip address 10.1.1.1 255.255.255.254
Device(config-if)# end

The following example shows how to enable the auto-IP functionality on the interfaces of a device:

Note

This configuration example applies to a device which is not being configured a seed device:


Device> enable
Device# configure terminal
Device(config)# lldp run
Device(config)# interface ethernet 0/1
Device(config-if)# auto-ip-ring 4 ipv4-address 10.1.1.3
Device(config-if)# exit
Device(config)# interface ethernet 1/1
Device(config-if)# auto-ip-ring 4 ipv4-address 10.1.1.3
Device(config-if)# end

Related Commands


Command	Description
debug auto-ip-ring	Debugs errors or events specific to an auto-IP ring.
show auto-ip-ring	Displays auto-IP ring information.

auto-ip-ring ipv4-auto

To enable automatic IP address configuration on an Auto-IP ring port from a pool of IP addresses, use the auto-ip-ring ipv4-auto command in interface configuration mode. To disable automatic IP address configuration on an Auto-IP ring port from a previously reserved pool of IP addresses, use the no form of this command.

auto-ip-ring ring-id ipv4-auto

no auto-ip-ring ring-id ipv4-auto

Syntax Description

ring-id

Auto-IP ring identification number. The ring ID must be the same for the two network-to-network interfaces (NNIs) of the node.

ipv4-auto

Automatically configures an IP address from a pool of IP addresses.

Remember

You must enable the auto-ip-ring ipv4-auto command on all Auto-IP ring ports for Zero touch Auto-IP functionality configuration.

Command Default

The automatic mode is disabled on an Auto-IP port.

Command Modes

Interface configuration (config-if)

Command History


Release	Modification
15.5(2)S	This command was introduced.
Cisco IOS XE Release 3.15S	This command was integrated into Cisco IOS XE Release 3.15S.

Usage Guidelines

The process of automatically configuring an IP address on an Auto-IP ring port from a pool of addresses forms a part of implementing the Zero touch Auto-IP functionality. Use the auto-ip-ring server (to implement a device as the Auto-IP server) and auto-ip-ring ipv4-seed (to create a port as seed port and initiate the automatic IP address configuration process) commands for other configurations of the Zero touch Auto-IP functionality.

Examples

The following example shows how to enable automatic IP address configuration on an Auto-IP ring port:


Device> enable
Device# configure terminal
Device(config)# lldp run
Device(config)# interface ethernet 0/0
Device(config-if)# auto-ip-ring 1 ipv4-auto
Device(config-if)# exit
Device(config)# end

Related Commands


Command	Description
debug auto-ip-ring	Debugs errors or events specific to an auto-IP ring.
show auto-ip-ring	Displays auto-IP ring information.

auto-ip-ring ipv4-seed

To configure an Auto-IP ring port as a seed port, use the auto-ip-ring ipv4-seed command in interface configuration mode. To remove the seed port status on an Auto-IP ring port, use the no form of this command.

auto-ip-ring ring-id ipv4-seed

no auto-ip-ring ring-id ipv4-seed

Syntax Description


`ring-id`	Auto-IP ring identification number.
ipv4-seed	Specifies the port as the seed port. An Auto-IP ring can have only one seed port.

Command Default

A seed port is not configured.

Command Modes

Interface configuration (config-if)

Command History


Release	Modification
15.5(2)S	This command was introduced.
Cisco IOS XE Release 3.15S	This command was integrated into Cisco IOS XE Release 3.15S.

Usage Guidelines

A seed port is an Auto-IP port that initiates the address allocation process. The priority of the seed port is set to 2 (priority of an owner port), an IP address is taken from the pool of IP addresses that is reserved in the Auto-IP server, and automatically configured for the port. The owner port assigns an IP address to its neighbor, a non-owner port. In a similar way, each owner port derives an IP address from the Auto-IP server for itself and also assigns an IP address to the neighbor, a non-owner port.

Examples

The following example shows how to configure an Auto-IP ring port as a seed port:


Device> enable
Device# configure terminal
Device(config)# interface ethernet 0/0
Device(config-if)# auto-ip-ring 1 ipv4-seed
Device(config-if)# exit

Related Commands


Command	Description
auto-ip-ring ipv4-auto	Enables automatic IP address configuration on an Auto-IP ring port from a pool of IP addresses.
auto-ip-ring server	Configures a device in an Auto-IP ring as the Auto-IP server.
show auto-ip-ring	Displays auto-IP ring information.

auto-ip-ring server

To configure a device in an Auto-IP ring as the Auto-IP server, use the auto-ip-ring server command in global configuration mode. To remove Auto-IP server status on a device, use the no form of this command.

auto-ip-ring server

no auto-ip-ring server

Syntax Description

This command has no arguments or keywords.

Command Default

No device in an Auto-IP ring is configured as an Auto-IP server.

Command Modes

Global configuration (config)

Command History


Release	Modification
15.5(2)S	This command was introduced.
Cisco IOS XE Release 3.15S	This command was integrated into Cisco IOS XE Release 3.15S.

Usage Guidelines

One device in an Auto-IP ring has to be configured as the Auto-IP server. After configuration, you have to reserve a pool of IP addresses for automatic assignment of IP addresses. A sample configuration of the Auto-IP server and reserving of a pool of IP addresses is given below:



!
Device(config)# auto-ip-ring server 
Device(config-auto-ip-server)# ipv4-address-pool 10.1.1.10 6
!

The Auto-IP server allocates IP addresses to the owner ports of the ring and each non-owner port derives its IP address from the owner port through LLDP.

Examples

The following example shows how to configure a device in an Auto-IP ring as the Auto-IP server:


Device> enable
Device# configure terminal
Device(config)# auto-ip-ring server 
Device(config-auto-ip-server)#

Related Commands


Command	Description
debug auto-ip-ring	Debugs errors or events specific to an Auto-IP ring.
ipv4-address-pool	Reserves a pool of IP addresses on the Auto-IP server.
show auto-ip-ring	Displays Auto-IP ring information.

basic-mapping-rule

To configure a basic mapping rule for the mapping of addresses and ports translation (MAP-T), use the basic-mapping-rule command in NAT64 MAP-T configuration mode. To remove the basic mapping rule, use the no form of this command.

basic-mapping-rule

no basic-mapping-rule

Syntax Description

This command has no arguments or keywords.

Command Default

Mapping rules are not enabled.

Command Modes

NAT64 MAP-T configuration (config-nat64-mapt)

Command History


Release	Modification
Cisco IOS XE Release 3.8S	This command was introduced.
Cisco IOS Release 15.5(2)T	This command was integrated into Cisco IOS Release 15.5(2)T.

Usage Guidelines

MAP-T or Mapping of addresses and ports (MAP) double stateless translation-based solution (MAP-T) provides IPv4 hosts connectivity to and across an IPv6 domain.

Examples

The following example shows how to configure the basic mapping rule mode:

Device(config)# nat64 map-t domain 3
Device(config-nat64-mapt)# basic-mapping-rule
Device(config-nat64-mapt-bmr)#

Related Commands


Command	Description
nat64 map-t	Configures NAT64 MAP-T settings.

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


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

Command Default

No default behavior or values.

Command Modes

DHCP pool configuration

Command History


Release	Modification
12.0(1)T	This command was introduced.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Examples

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


bootfile xllboot

Related Commands


Command	Description
ip dhcp pool	Configures a DHCP address pool on a Cisco IOS DHCP Server and enters DHCP pool configuration mode.
next-server	Configures the next server in the boot process of a DHCP client.

cache-memory-max

To allocate a portion of the system memory for cache, use the cache-memory-max command in multicast Domain Name System (mDNS) configuration mode. To remove the allocation of a portion of the system memory for cache, use the no form of this command.

cache-memory-max cache-config-percentage

no cache-memory-max cache-config-percentage

Syntax Description

cache-config-percentage

Portion of the system memory, in percentage, that is allocated for cache.

Note

By default, 10 % system memory is allocated for cache. You must use the cache-memory-max command to increase the cache memory allocation.

Command Default

10 % system memory is allocated for cache.

Command Modes

Multicast DNS configuration (config-mdns)

Command History


Release	Modification
15.2(1)E	This command was introduced.

Usage Guidelines

You must specify the system memory portion that you want to reserve for cache as a number, without the percentage symbol (%). For 20% allocation for cache memory, you must enter the value 20.

Examples

The following example shows system memory allocation for cache being increased to 20 %:


Device> enable
Device# configure terminal
Device(config)# service-routing mdns-sd
Device(config-mdns)# cache-memory-max 20
Device(config-mdns)# exit

Related Commands


Command	Description
service-routing mdns-sd	Enables mDNS gateway functionality for a device.

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


`class-name`	Name of the DHCP class.

Command Default

No class is associated with the DHCP address pool.

Command Modes

DHCP pool configuration (dhcp-config)

Command History


Release	Modification
12.2(13)ZH	This command was introduced.
12.3(4)T	This command was integrated into Cisco IOS Release 12.3(4)T.
12.2(28)SB	This command was integrated into Cisco IOS Release 12.2(28)SB.
12.2(33)SRB	This command was integrated into Cisco IOS Release 12.2(33)SRB.
15.0(1)S	This command was integrated into Cisco IOS Release 15.0(1)S.

Usage Guidelines

You must first define the class using the ip dhcp class command available in 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 shows how to associate DHCP class 1 and class 2 with a DHCP pool named pool1:


Router(config)# ip dhcp pool pool1
Router(dhcp-config)# network 10.0.20.0 255.255.255.0
Router(dhcp-config)# class class1
Router(config-dhcp-pool-class)# address range 10.0.20.1 10.0.20.100
Router(config-dhcp-pool-class)# exit
Router(dhcp-config)# class class2
Router(config-dhcp-pool-class)# address range 10.0.20.101 10.0.20.200

Related Commands


Command	Description
ip dhcp class	Defines a DHCP class and enters DHCP class configuration mode.

clear arp interface

To clear the entire Address Resolution Protocol (ARP) cache on an interface, use the clear arp interface command in privileged or user EXEC mode.

clear arp interface type number

Syntax Description


`type`	Interface type.
`number`	Interface number.

Command Default

No default behavior or values.

Command Modes

Privileged or User EXEC

Command History


Release	Modification
12.0(22)S	This command was introduced.
12.2(15)T	This command was integrated into Cisco IOS Release 12.2(15)T.
12.2(18)S	This command was integrated into Cisco IOS Release 12.2(18)S.
12.2(27)SBC	This command was integrated into Cisco IOS Release 12.2(27)SBC.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Usage Guidelines

Use the clear arp interface command to clean up ARP entries associated with an interface.

Examples

The following example clears the ARP cache from Ethernet interface 0:


Router# clear arp interface ethernet 0

clear arp-cache

To refresh dynamically created entries from the Address Resolution Protocol (ARP) cache, use the clear arp-cache command in privileged EXEC mode.

clear arp-cache [interface type number | [vrf vrf-name] ip-address]

Syntax Description


interface `type` `number`	(Optional) Refreshes only the ARP table entries associated with this interface.
vrf `vrf-name`	(Optional) Refreshes only the ARP table entries for the specified Virtual Private Network (VPN) routing and forwarding (VRF) instance and the IP address specified by the `ip-address` argument.
`ip-address`	(Optional) Refreshes only the ARP table entries for the specified IP address.

Command Default

This command has no default settings.

Command Modes

Privileged EXEC

Command History


Release	Modification
12.0(22)S	This command was introduced.
12.2(15)T	This command was integrated into Cisco IOS Release 12.2(15)T.
12.2(27)SBC	This command was integrated into Cisco IOS Release 12.2(27)SBC.
12.4(11)T	The interface keyword and the `type` and `number` arguments were made optional to support refreshing of entries for a single router interface. The vrf keyword, the `vrf-name` argument, and the `ip-address` argument were added to support refreshing of entries of a specified address and an optionally specified VRF.
12.2(33)SRB	This command was integrated into Cisco IOS Release 12.2(33)SRB.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Usage Guidelines

This command updates the dynamically learned IP address and MAC address mapping information in the ARP table to ensure the validity of those entries. If the refresh operation encounters any stale entries (dynamic ARP entries that have expired but have not yet been aged out by an internal, timer-driven process), those entries are aged out of the ARP table immediately as opposed to at the next refresh interval.

Note

By default, dynamically learned ARP entries remain in the ARP table for four hours.

The clear arp-cache command can be entered multiple times to refresh dynamically created entries from the ARP cache using different selection criteria.

Use this command without any arguments or keywords to refresh all ARP cache entries for all enabled interfaces.
To refresh ARP cache entries for a specific interface, use this command with the interface keyword and type and number arguments.

Tip

The valid interface types and numbers can vary according to the router and the interfaces on the router. To list all the interfaces configured on a particular router, use the show interfaces command with the summary keyword. Use the appropriate interface specification, typed exactly as it is displayed under the Interface column of the show interfaces command output, to replace the type and number arguments in the clear arp-cache interface command.

To refresh ARP cache entries from the global VRF and for a specific host, use this command with the ip-address argument.
To refresh ARP cache entries from a named VRF and for a specific host, use this command with the vrf keyword and the vrf-name and ip-address arguments.

To display ARP table entries, use the show arp command.

This command does not affect permanent entries in the ARP cache, and it does not affect the ARP HA statistics:

To remove static ARP entries from the ARP cache, use the no form of the arp command.
To remove alias ARP entries from the ARP cache, use the no form of the arp command with the alias keyword.
To reset the ARP HA status and statistics, use the clear arp-cache counters ha command.

Examples

The following example shows how to refresh all dynamically learned ARP cache entries for all enabled interfaces:


Router# clear arp-cache

The following example shows how to refresh dynamically learned ARP cache entries for the Ethernet interface at slot 1, port 2:


Router# clear arp-cache interface ethernet 1/2

The following example shows how to refresh dynamically learned ARP cache entries for the host at 192.0.2.140:


Router# clear arp-cache 192.0.2.140

The following example shows how to refresh dynamically learned ARP cache entries from the VRF named vpn3 and for the host at 192.0.2.151:


Router# clear arp-cache vrf vpn3 192.0.2.151

Related Commands


Command	Description
arp (global)	Configures a permanent entry in the ARP cache.
arp timeout	Configures how long a dynamically learned IP address and its corresponding MAC address remain in the ARP cache.
clear arp-cache counters ha	Resets the ARP HA statistics.
show arp	Displays ARP table entries.
show interfaces	Displays statistics for all interfaces configured on the router or access server.

clear arp-cache counters ha

To reset the Address Resolution Protocol (ARP) high availability (HA) statistics, use the clear arp-cache counters ha command in privileged EXEC mode.

clear arp-cache counters ha

Syntax Description

This command has no arguments or keywords.

Command Default

No default behavior or values.

Command Modes

Privileged EXEC

Command History


Release	Modification
12.4(11)T	This command was introduced.
12.2(31)SB2	This command was integrated into Cisco IOS Release 12.2(31)SB2.
12.2(33)SRB	This command was integrated into Cisco IOS Release 12.2(33)SRB.

Usage Guidelines

Use the clear arp-cache counters ha command to reset all ARP high availability statistics for all enabled interfaces.

To display the ARP HA status and statistics, use the show arp ha command.

Note

The clear arp-cache counters ha command and the show arp ha command are available only on HA-capable platforms (that is, Cisco networking devices that support dual Route Processors [RPs]).

Examples

The following example shows how to reset the ARP HA statistics:


Router# clear arp-cache counters ha

Related Commands


Command	Description
clear arp-cache	Refreshes dynamically learned entries in the ARP cache.
show arp ha	Displays the ARP HA status and statistics.

clear host

To delete hostname-to-address mapping entries from one or more hostname caches, use the clear host command in privileged EXEC mode.

clear host [view view-name | vrf vrf-name | all] {hostname | *}

Syntax Description


view `view-name`	(Optional) The `view-name` argument specifies the name of the Domain Name System (DNS) view whose hostname cache is to be cleared. Default is the default DNS view associated with the specified or global Virtual Private Network (VPN) routing and forwarding (VRF) instance.
vrf `vrf-name`	(Optional) The `vrf-name` argument specifies the name of the VRF associated with the DNS view whose hostname cache is to be cleared. Default is the global VRF (that is, the VRF whose name is a NULL string) with the specified or default DNS view.
all	(Optional) Specifies that hostname-to-address mappings are to be deleted from the hostname cache of every configured DNS view.
`hostname`	Name of the host for which hostname-to-address mappings are to be deleted from the specified hostname cache.
*	Specifies that all the hostname-to-address mappings are to be deleted from the specified hostname cache.

Command Default

No hostname-to-address mapping entries are deleted from any hostname cache.

Command Modes

Privileged EXEC

Command History


Release	Modification
10.0	This command was introduced.
12.4(4)T	The vrf keyword, `vrf-name` argument, and all keyword were added.
12.4(9)T	The view keyword and `view-name` argument were added.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Usage Guidelines

This command clears the specified hostname cache entries in running memory, but it does not remove the entries from NVRAM.

Entries can be removed from the hostname caches for a DNS view name, from the hostname caches for a VRF, or from all configured hostname caches. To remove entries from hostname caches for a particular DNS view name, use the view keyword and view-name argument. To remove entries from the hostname caches for a particular VRF, use the vrf keyword and vrf-name argument. To remove entries from all configured hostname caches, use the all keyword.

To remove entries that provide mapping information for a single hostname, use the hostname argument. To remove all entries, use the * keyword.

To display the cached list of hostnames and addresses specific to a particular DNS view or for all configured DNS views, use the show hosts command.

To define static hostname-to-address mappings in the DNS hostname cache for a DNS view, use the ip host command.

Examples

The following example shows how to clear all entries from the hostname cache for the default view in the global address space:


Router# clear host all *

The following example shows how to clear entries for the hostname www.example.com from the hostname cache for the default view associated with the VPN named vpn101:


Router# clear host vrf vpn101 www.example.com

The following example shows how to clear all entries from the hostname cache for the view named user2 in the global address space:


Router# clear host view user2 *

Related Commands


Command	Description
ip host	Defines static hostname-to-address mappings in the DNS hostname cache for a DNS view.
show hosts	Displays the default domain name, the style of name lookup service, a list of name server hosts, and the cached list of hostnames and addresses specific to a particular DNS view or for all configured DNS views.

clear ip arp inspection log

To clear the status of the log buffer, use the clear ip arp inspection log command in privileged EXEC mode.

clear ip arp inspection log

Syntax Description

This command has no arguments or keywords.

Command Default

This command has no default settings.

Command Modes

Privileged EXEC

Command History


Release	Modification
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.

Examples

This example shows how to clear the contents of the log buffer:


Router# 
clear ip arp inspection log

Related Commands


Command	Description
arp access-list	Configures an ARP ACL for ARP inspection and QoS filtering and enter the ARP ACL configuration submode.
show ip arp inspection log	Displays the status of the log buffer.

clear ip arp inspection statistics

To clear the dynamic ARP inspection statistics, use the clear ip arp inspection statistics command in privileged EXEC mode.

clear ip arp inspection statistics [vlan vlan-range]

Syntax Description


vlan `vlan-range`	(Optional) Specifies the VLAN range.

Command Default

This command has no default settings.

Command Modes

Privileged EXEC

Command History


Release	Modification
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.

Examples

This example shows how to clear the DAI statistics from VLAN 1:


Router# clear ip arp inspection statistics vlan 1

Related Commands


Command	Description
arp access-list	Configures an ARP ACL for ARP inspection and QoS filtering and enter the ARP ACL configuration submode.
clear ip arp inspection log	Clears the status of the log buffer.
show ip arp inspection log	Displays the status of the log buffer.

clear ip arp poll statistics

To clear the IP Address Resolution Protocol (ARP) host polling information, use the clear ip arp poll statistics command in privileged EXEC mode.

clear ip arp poll statistics

Syntax Description

This command has no arguments or keywords.

Command Modes

Privileged EXEC (#)

Command History


Release	Modification
15.1(1)SY	This command was introduced.

Examples

The following example shows how to clear the IP ARP host polling information:

Device# clear ip arp poll statistics

Related Commands


Command	Description
ip arp poll	Configures IP ARP polling for unnumbered interfaces.
show ip arp poll	Displays the IP ARP host polling status.

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 [vrf vrf-name] {* | address}

Syntax Description


pool `name`	(Optional) Specifies the name of the DHCP pool.
vrf	(Optional) Clears virtual routing and forwarding (VRF) information from the DHCP database.
`vrf-name`	(Optional) The VRF name.
*	Clears all automatic bindings.
`address`	The address of the binding you want to clear.

Command Modes

Privileged EXEC (#)

Command History


Release	Modification
12.0(1)T	This command was introduced.
12.2(8)T	The pool keyword and `name` argument were added.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Cisco IOS XE Release 2.6	This command was modified. The vrf keyword and `vrf-name` argument were added.

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 binding command in global configuration mode to delete a manual binding.

Note the following behavior for the clear ip dhcp binding command:

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 nonvirtual VRF DHCP pools for the specified binding.
If you do not specify the pool name option and the * option is specified, it is assumed that all automatic or on-demand bindings in all VRF and non-VRF pools are to be deleted.
If you specify both the pool name option and the * option, all automatic or on-demand bindings in the specified pool only will be cleared.
If you specify the pool name option and an IP address, the specified binding will be deleted from the specified pool.

Examples

The following example shows how to delete the address binding 10.12.1.99 from a DHCP server database:


Router# clear ip dhcp binding 10.12.1.99

The following example shows how to delete all bindings from all pools:


Router# clear ip dhcp binding *

The following example shows how to delete all bindings from the address pool named pool1:


Router# clear ip dhcp pool pool1 binding *

The following example shows how to delete address binding 10.13.2.99 from the address pool named pool2:


Router# clear ip dhcp pool pool2 binding 10.13.2.99

The following example shows how to delete VRF vrf1 from the DHCP database:


Router# clear ip dhcp binding vrf vrf1 10.13.2.99

Related Commands


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

clear ip dhcp conflict

To clear an address conflict from the Dynamic Host Configuration Protocol (DHCP) server database, use the clear ip dhcp conflict command in privileged EXEC mode.

clear ip dhcp [pool name] conflict [vrf vrf-name] {* | address}

Syntax Description


pool `name`	(Optional) Specifies the name of the DHCP pool.
vrf	(Optional) Clears DHCP virtual routing and forwarding (VRF) conflicts.
`vrf-name`	(Optional) The VRF name.
*	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


Release	Modification
12.0(1)T	This command was introduced.
12.2(8)T	The pool keyword and `name` argument were added.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Cisco IOS XE Release 2.6	This command was modified. The vrf keyword and `vrf-name` argument were added.

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:

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 nonvirtual VRF DHCP pools for the specified conflict.
If you do not specify the pool name option and the * option is specified, it is assumed that all automatic/ or on-demand conflicts in all VRF and non-VRF pools are to be deleted.
If you specify both the pool name option and the * option, all automatic or on-demand conflicts in the specified pool only will be cleared.
If you specify the pool name option and an IP address, the specified conflict will be deleted from the specified pool.

Examples

The following example shows how to delete an address conflict of 10.12.1.99 from the DHCP server database:


Router# clear ip dhcp conflict 10.12.1.99

The following example shows how to delete all address conflicts from all pools:


Router# clear ip dhcp conflict *

The following example shows how to delete all address conflicts from the address pool named pool1:


Router# clear ip dhcp pool pool1
conflict *

The following example shows how to delete address conflict 10.13.2.99 from the address pool named pool2:


Router# clear ip dhcp pool pool2 conflict 10.13.2.99

The following example shows how to delete VRF vrf1 from the DHCP database:


Router# clear ip dhcp conflict vrf vrf1 10.13.2.99

Related Commands


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

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 [type number]

Syntax Description


`type`	(Optional) Interface type. For more information, use the question mark (?) online help function.
`number`	(Optional) Interface or subinterface number. For more information about the numbering system for your networking device, use the question mark (?) online help function.

Command Modes

Privileged EXEC (#)

Command History


Release	Modification
12.2(33)SRC	This command was introduced.

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 lease
Interface        Count
Serial0/0.1      5
Serial1          3
Router# clear ip dhcp limit lease
Router# show ip dhcp limit lease

Related Commands


Command	Description
ip dhcp limit lease	Limits the number of leases offered to DHCP clients per interface.
ip dhcp limit lease per interface	Limits the number of DHCP leases offered to DHCP clients behind an ATM RBE unnumbered or serial unnumbered interface.
show ip dhcp limit lease	Displays the number of times the lease limit threshold has been violated on an interface.

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


Release	Modification
12.0(1)T	This command was introduced.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

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 statistics

Related Commands


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

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.

Command Default

This command has no default settings.

Command Modes

Privileged EXEC

Command History


Release	Modification
12.2(14)SX	Support for this command was introduced on the Supervisor Engine 720.
12.2(17d)SXB	Support for this command on the Supervisor Engine 2 was extended to Release 12.2(17d)SXB.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.

Examples

This example shows how to clear the DHCP-snooping binding-entry table:


Router# clear ip dhcp snooping binding

clear 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


Release	Modification
12.2(14)SX	Support for this command was introduced on the Supervisor Engine 720.
12.2(17d)SXB	Support for this command on the Supervisor Engine 2 was extended to Release 12.2(17d)SXB.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.

Examples

The following example shows how to clear the statistics from the DHCP binding database:


Router# clear ip dhcp snooping database statistics

clear 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.

Command Default

This command has no default settings.

Command Modes

Privileged EXEC

Command History


Release	Modification
12.2(14)SX	Support for this command was introduced on the Supervisor Engine 720.
12.2(17d)SXB	Support for this command on the Supervisor Engine 2 was extended to Release 12.2(17d)SXB.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.

Examples

This example shows how to clear the DHCP snooping statistics:


Router# clear ip dhcp snooping statistics

clear 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


Release	Modification
12.2(8)T	This command was introduced.

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:

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 subnet.
If you do not specify the pool name option and the * option is specified, it is assumed that all automatic or on-demand subnets in all VRF and non-VRF pools are to be deleted.
If you specify both the pool name option and the * option, all automatic or on-demand subnets in the specified pool only will be cleared.
If you specify the pool name option and an IP address, the subnet containing the specified IP address will be deleted from the specified pool.

Caution

Use this command with caution to prevent undesired termination of active PPP sessions.

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 10.0.0.2

The 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 10.0.0.2

Related Commands


Command	Description
show ip dhcp pool	Displays information about the DHCP address pools.

clear ip interface

To clear the IP interface statistics, use the clear ip interface command in privileged EXEC mode.

clear ip interface type number [stats | | topology {instance-name | all | base} stats]

Syntax Description


`type` `number`	Interface type and number.
stats	(Optional) Clears the statistics summary.
topology	(Optional) Clears topology statistics.
`instance-name`	(Optional) Name of the instance for which topology statistics are to be cleared.
all	(Optional) Clears all topology statistics.
base	(Optional) Clears base topology statistics.

Command Modes

Privileged EXEC (#)

Command History


Release	Modification
15.1(1)SY	This command was introduced.

Usage Guidelines

The interface that borrows its address from one of the device’s other functional interfaces is called the unnumbered interface. The IP unnumbered interfaces help in conserving network and address space. Use the clear ip interface command to clear the IP interface statistics for IP numbered and unnumbered interfaces.

Examples

The following example shows how to clear all topology statistics for a loopback interface:

Device(#)clear ip interface loopback0 topology all stats

Related Commands


Command	Description
show ip interface	Displays the usability status of interfaces configured for IP.
show ip interface unnumbered	Displays the status of unnumbered interface support on specific interfaces.

clear ip nat translation

To clear dynamic Network Address Translation ( NAT) translations from the translation table, use the clear ip nat translation command in EXEC mode.

clear ip nat translation {* | forced | [piggyback-internal | esp | tcp | udp] [inside global-ip [global-port] local-ip [local-port] outside local-ip global-ip] | [inside global-ip local-ip [forced]] | [outside local-ip global-ip [forced]]}

Syntax Description


*	Clears all dynamic translations.
forced	(Optional) Forces the clearing of either: all dynamic entries, whether or not there are any child translations. a single dynamic half-entry and any existing child translations, whether or not there are any child translations.
piggyback-internal	(Optional) Clears translations created off of piggyback data.
esp	(Optional) Clears Encapsulating Security Payload (ESP) entries from the translation table.
tcp	(Optional) Clears the TCP entries from the translation table.
udp	(Optional) Clears the User Datagram Protocol (UDP) entries from the translation table.
inside	(Optional) Clears the inside translations containing the specified `global-ip` and `local-ip` addresses. If used without the forced keyword, clears only those entries that do not have child translations.
`global-ip`	(Optional) Global IP address.
`global-port`	(Optional) Global port.
`local-ip`	(Optional) Local IP address.
`local-port`	(Optional) Local port.
outside	(Optional) Clears the outside translations containing the specified `local-ip` and `global-ip` addresses. If used without the forced keyword, clears only those entries that do not have child translations.

Command Modes

EXEC

Command History


Release	Modification
11.2	This command was introduced.
12.2(15)T	The esp keyword was added.
12.2 (33) XND	The forced keyword was extended to support the removal of a half entry regardless of whether it has any child translations.
12.4(2)T	The piggyback-internal keyword was added.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
XE 2.4.2	The forced keyword was extended to support the removal of a half entry regardless of whether it has any child translations.

Usage Guidelines

Use this command to clear entries from the translation table before they time out.

Examples

The following example shows the NAT entries before and after the User Datagram Protocol (UDP) entry is cleared:


Router> show ip nat translations
Pro Inside global        Inside local       Outside local      Outside global
udp 10.69.233.209:1220  10.168.1.95:1220   10.69.2.132:53     10.69.2.132:53
tcp     10.69.233.208       10.168.1.94 
tcp 10.69.233.209:11012 10.168.1.89:11012  10.69.1.220:23     10.69.1.220:23
tcp 10.69.233.209:1067  10.168.1.95:1067   10.69.1.161:23     10.69.1.161:23
Router# clear ip nat translation udp inside 10.69.233.209 1220 10.168.1.95 1220
outside 10.69.2.132 53 10.69.2.132 53
Router# show ip nat translations
 
Pro     Inside global       Inside local       Outside local      Outside global
tcp     10.69.233.208       10.168.1.94 
tcp     10.69.233.209:11012 10.168.1.89:11012  10.69.1.220:23     10.69.1.220:23
tcp     10.69.233.209:1067  10.168.1.95:1067   10.69.1.161:23     10.69.1.161:23
Router# clear ip nat translation inside 10.69.233.208 10.168.1.94 forced
Router# show ip nat translations
 
Pro     Inside global       Inside local       Outside local      Outside global
tcp     10.69.233.209:11012 10.168.1.89:11012  10.69.1.220:23     10.69.1.220:23
tcp     10.69.233.209:1067  10.168.1.95:1067   10.69.1.161:23     10.69.1.161:23

Related Commands


Command	Description
ip nat	Designates that traffic originating from or destined for the interface is subject to NAT.
ip nat inside destination	Enables NAT of the inside destination address.
ip nat inside source	Enables NAT of the inside source address.
ip nat outside source	Enables NAT of the outside source address.
ip nat pool	Defines a pool of IP addresses for NAT.
ip nat service	Changes the amount of time after which NAT translations time out.
show ip nat statistics	Displays NAT statistics.
show ip nat translations	Displays active NAT translations.

clear ip nat translation redundancy

To clear IP Network Address Translation (NAT) redundancy translations, use the clear ip nat translation redundancy command in privileged EXEC mode.

clear ip nat translation redundancy RG-id {* | forced}

Syntax Description


*	Clears all dynamic translations.
forced	Clears all dynamics forcefully.

Command Modes

Privileged EXEC

Command History


Release	Modification
15.3(2)T	This command was introduced.

Usage Guidelines

Use the clear ip nat translation redundancy command to clear IP NAT redundancy translations. It is not recommended to execute this command on a device which is currently in the standby redundancy state.

Examples

The following example shows how to all clear IP NAT redundancy translations.

Device# clear ip nat translation redundancy *

Related Commands


Command	Description
show ip nat redundancy	Displays NAT redundancy information
show ip nat translations redundancy	Displays active NAT translations.

clear ip nhrp

To clear all dynamic entries from the Next Hop Resolution Protocol (NHRP) cache, use the clear ip nhrp command in user EXEC or privileged EXEC mode.

clear ip nhrp [dest-ip-address [dest-mask]] [counters | [interface | {tunnel number | Virtual-Access number} | vrf vrf-name]] [shortcut | [interface | {tunnel number | Virtual-Access number}]]

Syntax Description


`dest-ip-address`	(Optional) Destination IP address. Specifying this argument clears NHRP mapping entries for the specified destination IP address.
`dest-mask`	(Optional) Destination network mask.
counters	(Optional) Clears the NHRP counters.
interface	(Optional) Clears the NHRP mapping entries for all interfaces.
tunnel `number`	Removes the specified interface name from the NHRP cache that all entries learned using this tunnel interface.
Virtual-Access `number`	Removes the specified interface name from the NHRP cache that all entries learned using this virtual access interface.
vrf	(Optional) Deletes entries from the NHRP cache for the specified VPN Routing and Forwarding (VRF) and Front VRF (FVRF).
`vrf-name`	Name of the VRF address family to which the command is applied.
shortcut	(Optional) Deletes shortcut entries from the NHRP cache.

Command Modes

User EXEC (>)

Privileged EXEC (#)

Command History


Release	Modification
11.0	This command was introduced.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.
Cisco IOS XE Release 2.5	This command was modified. The shortcut keyword was added.
15.3(2)T	This command was modified. The behavior of the interface keyword was updated to clear NHRP mapping entries for all interfaces. The Virtual-Access `number` keyword-argument pair was added.

Usage Guidelines

The clear ip nhrp command does not clear any static (configured) IP-to-NBMA address mappings from the NHRP cache. The clear ip nhrp shortcut command clears NHRP cache entries that have associated NHRP routes or next-hop overrides in the Routing Information Base (RIB).

The clear ip nhrp command clears Front VRF (FVRF) counters. It does not clear Internal VRF (IVRF) counters.

Replacing ip in the command name with ipv6 clears IPv6-specific cache.

Examples

The following example shows how to clear all dynamic entries from the NHRP cache for an interface:


Device# clear ip nhrp

The following example shows how to clear the NHRP cache entries that have associated NHRP routes or next-hop overrides in the RIB:


Device# clear ip nhrp shortcut

Related Commands


Command	Description
show ip nhrp	Displays NHRP mapping information.

clear ip route

To delete routes from the IP routing table, use the clear ip route command in EXEC mode.

clear ip route {network [mask] | *}

Syntax Description


`network`	Network or subnet address to remove.
`mask`	(Optional) Subnet address to remove.
*	Removes all routing table entries.

Command Default

All entries are removed.

Command Modes

EXEC

Command History


Release	Modification
10.0	This command was introduced.
12.2(33)SRA	This command was integrated into Cisco IOS Release 12.2(33)SRA.
12.2SX	This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Examples

The following example removes a route to network 10.5.0.0 from the IP routing table:


Router> clear ip route 10.5.0.0

Bias-Free Language

Results

Chapter: accounting DHCP through clear ip route

accounting DHCP through clear ip route

accounting (DHCP)

Syntax Description

Command Default

Command Modes

Command History

Usage Guidelines

Examples

Related Commands

accounting (DHCP for IPv6)

Syntax Description

Command Default

Command Modes

Command History

Usage Guidelines

Examples

address client-id

Syntax Description

Command Default

Command Modes

Command History

Usage Guidelines

Examples

Related Commands

address hardware-address

Syntax Description

Command Default

Command Modes

Command History

Usage Guidelines

Examples

Related Commands

address prefix

Syntax Description

Command Default

Command Modes

Command History

Usage Guidelines

Examples

Related Commands

address range

Syntax Description

Command Default

Command Modes

Command History

Usage Guidelines

Examples

Related Commands

application redundancy

Syntax Description

Command Default

Command Modes

Command History

Examples

Related Commands

alg sip blacklist

Syntax Description

Command Default

Command Modes

Command History

Usage Guidelines

Examples

Related Commands

alg sip processor

Syntax Description

Command Default

Command Modes

Command History

Usage Guidelines

Examples

Related Commands

alg sip timer

Syntax Description

Command Default

Command Modes

Command History