Cisco Systems 32369 Overview
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1. IP address Hardware address Lease expiration Type 172 16 2 254 02c7 800 0422 Infinite Manual Table 2 show ip dhcp Field Descriptions Field Description IP address The IP address of the host as recorded on the DHCP server Hardware address The MAC address or client identifier of the host as recorded on the DHCP server Lease expiration The lease expiration date of the IP address of the host Type The manner in which the IP address was assigned to the host Cisco IOS DHCP Server 43 Command Reference Related Commands clear ip dhcp binding 44 Release 12 0 1 T show ip dhcp conflict show ip dhcp conflict To display address conflicts found by a Cisco IOS Dynamic Host Configuration Protocol DHCP Server when addresses are offered to the client use the show ip dhcp conflict EXEC command show ip dhcp conflict address Syntax Description address Optional Specifies the IP address of the conflict found Defaults None Command Modes EXEC Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T The server detects conflicts using ping The client detects conflicts using gratuitous Address Resolution Protocol ARP If an address conflict is detected the address is removed from the pool and the address will not be assigned until an administrator resolves the conflict Examples The following example displays the detection method and detection time for all IP addresses the DHCP server has offered2. no ip dhcp conflict logging Related Commands clear ip dhcp conflict ip dhcp database show ip dhcp conflicts Cisco IOS DHCP Server 25 Command Reference ip dhcp database You can configure a Cisco IOS Dynamic Host Configuration Protocol DHCP Server to save automatic bindings on a remote host called a database agent To configure a DHCP server database agent and database agent parameters use the ip dhcp database global configuration command Use the no form of this command to remove the database agent ip dhcp database ur timeout seconds write delay seconds no ip dhcp database url Syntax Description url Specifies the remote file used to store the automatic bindings Following are the acceptable URL file formats e tftp host filename ftp user password host filename e rcp user host filename timeout seconds Optional Specifies how long in seconds the DHCP server should wait before aborting a database transfer Transfers that exceed the timeout period are aborted By default DHCP waits 300 seconds before aborting a database transfer Infinity is defined as 0 seconds write delay seconds Optional Specifies how soon the DHCP server should send database updates By default DHCP waits 300 seconds 5 minutes before sending database changes The minimum delay is 60 seconds Defaults DHCP waits 300 seconds for both a write delay and a timeout Command Modes Global configuration Usage Guidelin
3. Cisco IOS DHCP Server Feature Overview Dynamic Host Control Protocol DHCP enables you to automatically assign reusable IP addresses to DHCP clients The Cisco IOS DHCP Server feature is a full DHCP server implementation that assigns and manages IP addresses from specified address pools within the router to DHCP clients If the Cisco IOS DHCP Server cannot satisfy a DHCP request from its own database it can forward the request to one or more secondary DHCP servers defined by the network administrator Figure 1 shows the basic steps that occur when a DHCP client requests an IP address from a DHCP server The client Host A sends a DHCPDISCOVER broadcast message to locate a Cisco IOS DHCP Server A DHCP server offers configuration parameters such as an IP address a MAC address a domain name and a lease for the IP address to the client in a DHSCPOFFER unicast message Figure 1 DHCP Request for an IP Address from a DHCP Server DHCPDISCOVER broadcast gt Cisco IOS DHCPOFFER unicast DHCP server DHCPREQUEST broadcast z DHCPACK unicast e Note A DHCP client may receive offers from multiple DHCP servers and can accept any one of the offers however the client usually accepts the first offer it receives Additionally the offer from the DHCP server is not a guarantee that the IP address will be allocated to the client however the server usually reserves the address until the client has had a chance to formally request the
4. DHCP Address Pool Configuration Example In the following example three DHCP address pools are created one in network 172 16 0 0 one in subnetwork 172 16 1 0 and one in subnetwork 172 16 2 0 Attributes from network 172 16 0 0 such as the domain name DNS server NetBIOS name server and NetBIOS node type are inherited in subnetworks 172 16 1 0 and 172 16 2 0 In each pool clients are granted 30 day leases and all addresses in each subnetwork except the excluded addresses are available to the DHCP server for assigning to clients Table 1 lists the IP addresses for the devices in three DHCP address pools Table 1 DHCP Address Pool Devices Pool 0 Network 172 16 0 0 Pool 1 Subnetwork 172 16 1 0 Pool 2 Subnetwork 172 16 2 0 Device IP Address Device IP Address Device IP Address Default routers Default routers 172 16 1 100 Default routers 172 16 2 100 172 16 1 101 172 16 2 101 DNS server 172 16 1 102 172 16 2 102 NetBIOS name server 172 16 1 103 172 16 2 103 NetBIOS node type h node 10 Release 12 0 1 T Manual Bindings Configuration Example ip dhcp database ftp user password 172 16 4 253 router dhcp write delay 120 ip dhcp excluded address 172 16 1 100 172 16 1 103 ip dhcp excluded address 172 16 2 100 172 16 2 103 ip dhcp pool 0 network 172 16 0 0 16 domain name cisco com dns server 172 16 1 102 172 16 2 102 netbios name server 172 16 1 103 17
5. DHCP server assumes that all pool addresses may be assigned to clients Use this command to exclude a single IP address or a range of IP addresses Example The following example configures an excluded IP address range from 172 16 1 100 through 172 16 1 199 ip dhcp excluded address 172 16 1 100 172 16 1 199 Related Commands ip dhcp pool network DHCP 28 Release 12 0 1 T ip dhcp ping packets ip dhcp ping packets To specify the number of packets a Cisco IOS Dynamic Host Configuration Protocol DHCP Server sends to a pool address as part of a ping operation use the ip dhep ping packets global configuration command Use the no form of this command to prevent the server from pinging pool addresses ip dhep ping packets count no ip dhcp ping packets Syntax Description count Indicates the number of ping packets that are sent before assigning the address to a requesting client The default value is two packets Defaults Two packets Command Modes Global configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T The DHCP server pings a pool address before assigning the address to a requesting client If the ping is unanswered the DHCP server assumes with a high probability that the address is not in use and assigns the address to the requesting client Examples The following example specifies five ping attempts by the DHCP server before ceasing any further ping attempts ip d
6. IP addresses within a general grouping of networks To configure the NetBIOS WINS servers that are available to a Microsoft DHCP client use the following command in DHCP pool configuration mode Command Purpose Router config dhcp netbios name server Specifies the NetBIOS WINS server that is available to a address address2 address8 Microsoft DHCP client One address is required however you can specify up to eight addresses in one command line 6 Release 12 0 1 T Configuring the NetBIOS Node Type for the Client Configuring the NetBIOS Node Type for the Client The NetBIOS node type for Microsoft DHCP clients can be one of four settings broadcast peer to peer mixed or hybrid To configure the NetBIOS node type for a Microsoft DHCP use the following command in DHCP pool configuration mode Command Purpose Router config dhcp netbios node type Specifies the NetBIOS node type for a Microsoft DHCP client type Configuring the Default Router for the Client After a DHCP client has booted the client begins sending packets to its default router The IP address of the default router should be on the same subnet as the client To configure a default router for a DHCP client use the following command in DHCP pool configuration mode Command Purpose Router config dhcp default router Specifies the IP address of the default router for a DHCP client address address2 address8 One IP address is required alt
7. The number of expired leases Malformed messages The number of truncated or corrupted messages that were received by the DHCP server Message The DHCP message type that was received by the DHCP server Received The number of DHCP messages that were received by the DHCP server Sent The number of DHCP messages that were sent by the DHCP server Related Commands clear ip dhep server statistics Cisco IOS DHCP Server 49 Debug Commands Debug Commands This section describes the following new debug command debug ip dhcp server 50 Release 12 0 1 T debug ip dhcp server debug ip dhcp server To enable Cisco IOS Dynamic Host Configuration Protocol DHCP Server debugging use the debug ip dhcp server privileged EXEC command Use the no form of this command to disable DHCP server debugging debug ip dhcp server events packets linkage no debug ip dhcp server events packets linkage Syntax Description events packets linkage Defaults Reports server events like address assignments and database updates Decodes DHCP receptions and transmissions Displays database linkage information such as parent child relationships in a radix tree DHCP server debugging is not enabled Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Examples The first example below shows a combination of DHCP server events and decoded receptions and transmissions Th
8. address b7 0813 8811 66 in dotted hexadecimal notation client identifier 01b7 0813 8811 66 Related Commands hardware address host ip dhcp pool 18 Release 12 0 1 T client name client name To specify the name of a Dynamic Host Configuration Protocol DHCP client use the client name DHCP pool configuration command The client name should not include the domain name Use the no form of this command to remove the client name client name name no client name Syntax Description name Specifies the client s name using any standard ASCII character The client name should not include the domain name For example the name mars should not be specified as mars cisco com Defaults None Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Examples The following example specifies a string client that will be the name of the client client name clientl Related Commands host ip dhcp pool Cisco IOS DHCP Server 19 Command Reference default router To specify the default router list for a Dynamic Host Configuration Protocol DHCP client use the default router DHCP pool configuration command Use the no form of this command to remove the default router list default router address address2 address8 no default router Syntax Description address Specifies the IP address of a router One IP address is required although you can sp
9. for the lease expiration date is one day address conflict A duplication of use of the same IP address by two hosts During address assignment DHCP checks for conflicts using ping and gratuitous ARP If a conflict is detected the address is removed from the pool The address will not be assigned until the administrator resolves the conflict address pool The range of IP addresses assigned by the DHCP server Address pools are indexed by subnet number client Any host requesting configuration parameters database A collection of address pools and bindings database agent Any host storing the DHCP bindings database for example a Trivial File Transfer Protocol TFTP server DNS Domain Name System A system used in the Internet for translating names of network nodes into addresses automatic address allocation An address assignment method where a network administrator obtains an IP address for a client for a finite period of time or until the client explicitly relinquishes the address Automatic allocation is particularly useful for assigning an address to a client that will be connected to the network only temporarily or for sharing a limited pool of IP addresses among a group of clients that do not need permanent IP addresses Automatic allocation may also be a good choice for assigning an IP address to a new client being permanently connected to a network where IP addresses are sufficiently scarce that it is important to recl
10. most preferred server and so on Examples The following example specifies 10 12 1 99 as the IP address of the domain name server of the client dns server 10 12 1 99 Related Commands domain name ip dhcp pool Cisco IOS DHCP Server 21 Command Reference domain name To specify the domain name for a Dynamic Host Configuration Protocol DHCP client use the domain name DHCP pool configuration command Use the no form of this command to remove the domain name domain name domain no domain name Syntax Description domain Specifies the client s domain name string Defaults None Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Examples The following example specifies cisco com as the domain name of the client domain name cisco com Related Commands dns server ip dhcp pool 22 Release 12 0 1 T hardware address hardware address To specify the hardware address of a Dynamic Host Configuration Protocol DHCP client use the hardware address DHCP pool configuration command It is valid for manual bindings only Use the no form of this command to remove the hardware address hardware address hardware address type no hardware address Syntax Description hardware address Specifies the MAC address of the client s hardware platform type Indicates the protocol of the hardware platform Strings and values are acceptable The
11. string options are e ethernet e ieee802 The value options are e 1 10Mb Ethernet 6 IEEE 802 If no type is specified the default protocol is Ethernet Defaults Ethernet is the default type if none is specified Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Examples The following example specifies b708 1388 f166 as the MAC address of the client hardware address b708 1388 166 Related Commands client identifier host ip dhcp pool Cisco IOS DHCP Server 23 Command Reference host To specify the IP address and network mask for a manual binding to a Dynamic Host Configuration Protocol DHCP client use the host DHCP pool configuration command Use the no form of this command to remove the client s IP address host address mask prefix length no host Syntax Description address Specifies the IP address of the client mask Optional Specifies the network mask of the client prefix length Optional Specifies the number of bits that comprise the address prefix The prefix is an alternative way of specifying the network mask of the client The prefix length must be preceded by a forward slash Defaults None Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T If the mask and prefix length are unspecified DHCP examines its address pools If no mask is found in
12. that have conflicts with other devices Table 3 lists descriptions of the fields in the example Router gt show ip dhcp conflict IP address Detection Method Detection time 172 16 3 132 Ping Feb 16 1998 12 28 PM 172 16 1 64 Gratuitous ARP Feb 23 1998 08 12 AM Table 3 show ip dhcp conflict Field Descriptions Field Description IP Address The IP address of the host as recorded on the DHCP server Detection Method The manner in which the IP address of the hosts were found on the DHCP server Can be a ping or a gratuitous ARP Detection time The time when the conflict was found Related Commands clear ip dhep conflict ip dhcp ping packets ip dhcp ping timeout Cisco IOS DHCP Server 45 Command Reference show ip dhcp database To display Cisco IOS Dynamic Host Configuration Protocol DHCP Server database agent information use the show ip dhcp database Privileged EXEC command show ip dhcp database url Syntax Description url Optional Specifies the remote file used to store automatic DHCP bindings Following are the acceptable URL file formats e tftp host filename e ftp user password host filename e rcp user host filename Defaults If a URL is not specified all database agent records are shown Otherwise only information about the specified agent is displayed Command Modes Privileged EXEC Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Examples The follo
13. the show ip dhcp server statistics EXEC command show ip dhcp server statistics Syntax Description This command has no arguments or keywords Defaults None Command Modes EXEC Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Examples The following example displays DHCP server statistics Table 5 lists descriptions for each field in the example Router gt show ip dhcp server statistics Memory usage 40392 Address pools 3 Database agents t Automatic bindings 190 Manual bindings 1 Expired bindings 3 Malformed messages 0 Message Received BOOTREQUEST t2 DHCPDISCOVER 200 DHCPREQUEST 178 DHCPDECLINE 0 DHCPRELEASE 0 DHCP INFORM 0 Message Sent BOOTREPLY 12 DHCPOFFER 190 DHCPACK 172 DHCPNAK 6 48 Release 12 0 1 T show ip dhcp server statistics Table 5 show ip dhcp server statistics Field Descriptions Field Description Memory usage The number of bytes of RAM allocated by the DHCP server Address pools The number of configured address pools in the DHCP database Database agents The number of database agents configured in the DHCP database Automatic bindings The number of IP addresses that have been automatically mapped to the MAC addresses of hosts that are found in the DHCP database Manual bindings The number of IP addresses that have been manually mapped to the MAC addresses of hosts that are found in the DHCP database Expired bindings
14. the DHCP relay agent information option in forwarded BOOTREQUEST messages ip dhcp relay information option Related Commands ip dhep relay information check ip dhcp relay information policy Cisco IOS DHCP Server 33 Command Reference ip dhcp relay information policy To configure a Dynamic Host Configuration Protocol DHCP relay agent s information reforwarding policy what a DHCP relay agent should do if a message already contains relay information use the ip dhcp relay information policy global configuration command Use the no form of this command to restore the default relay information policy ip dhcp relay information policy drop keep replace no ip dhcp relay information policy Syntax Description drop Directs the DHCP relay agent to discard messages with existing relay information if the relay information option is already present keep Indicates that existing information is left unchanged on the DHCP relay agent replace Indicates that existing information is overwritten on the DHCP relay agent Defaults The DHCP server replaces existing relay information Command Modes Global configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T This command is used by cable modem termination systems When a DHCP relay agent receives a message from a another DHCP relay agent relay information might already be present in the message By default the relay information from
15. the previous relay agent is replaced Examples The following examples configure a DHCP relay agent to drop messages with existing relay information keep existing information and replace existing information ip dhcp relay information policy drop ip dhcp relay information policy keep ip dhcp relay information policy replace Related Commands ip dhep relay information check ip dhcp relay information option 34 Release 12 0 1 T lease lease To configure the duration of the lease for an IP address that is assigned from a Cisco IOS Dynamic Host Configuration Protocol DHCP Server to a DHCP client use the lease DHCP pool configuration command Use the no form of this command to restore the default value lease days hours minutes infinite no lease Syntax Description days Specifies the duration of the lease in numbers of days hours Optional Specifies the number of hours in the lease A days value must be supplied before you can configure an hours value minutes Optional Specifies the number of minutes in the lease A days value and an hours value must be supplied before you can configure a minutes value infinite Specifies the duration of the lease is unlimited Defaults One day Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Examples The following example shows a one day lease lease 1 The following example shows a one hour lease
16. 2 16 2 103 netbios node type h node ip dhcp pool 1 network 172 16 1 0 24 default router 172 16 1 100 172 16 1 101 lease 30 ip dhcp pool 2 network 172 16 2 0 24 default router 172 16 2 100 172 16 2 101 lease 30 Manual Bindings Configuration Example The following example creates a manual binding for a client named Mars cisco com The MAC address of the client is 02c7 800 0422 and the IP address of the client is 172 16 2 254 ip dhcp pool Mars host 172 16 2 254 hardware address 02c7 f 800 0422 ieee802 client name Mars Because attributes are inherited the previous configuration is equivalent to the following ip dhcp pool Mars host 172 16 2 254 mask 255 255 255 0 hardware address 02c7 f 800 0422 ieee802 client name Mars default router 172 16 2 100 172 16 2 101 domain name cisco com dns server 172 16 1 102 172 16 2 102 netbios name server 172 16 1 103 172 16 2 103 netbios node type h node Cisco IOS DHCP Server 11 Command Reference Command Reference This section documents new or modified commands All other commands used with this feature are documented in the Cisco IOS Release 12 0 command reference publications bootfile e clear ip dhcp binding e clear ip dhcp conflict clear ip dhcp server statistics client identifier e client name default router dns server domain name hardware address host ip dhcp conflict logging ip dhcp database ip d
17. Configuring a DHCP Address Pool You can configure a DHCP address pool with a name that is a symbolic string such as engineering or an integer such as 0 Configuring a DHCP address pool also places you in DHCP pool configuration mode identified by the config dhcp prompt from which you can configure pool parameters for example the IP subnet number and default router list To configure a DHCP address pool complete the required tasks in the following sections Configuring the DHCP Address Pool Name and Entering DHCP Pool Configuration Mode To configure the DHCP address pool name and enter DHCP pool configuration mode use the following command in global configuration mode Command Purpose Router config ip dhep pool name Creates a name for the DHCP server address pool and places you in DHCP pool configuration mode identified by the config dhcp prompt Cisco IOS DHCP Server 5 DHCP Configuration Task List Configuring the DHCP Address Pool Subnet and Mask To configure a subnet and mask for the newly created DHCP address pool which contains the range of available IP addresses that the DHCP server may assign to clients use the following command in DHCP pool configuration mode Command Purpose Router config dhcp network Specifies the subnet network number and mask of the DHCP network number mask prefix length address pool The prefix length specifies the number of bits that comprise the addre
18. S DHCP Server feature service dhcp no service dhcp Syntax Description This command has no keywords or arguments Defaults The feature is enabled Command Modes Global configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Examples The following example enables DHCP services on the DHCP server service dhcp 42 Release 12 0 1 T show ip dhcp binding show ip dhcp binding To display address bindings on the Cisco IOS Dynamic Host Configuration Protocol DHCP Server use the show ip dhcp binding EXEC command show ip dhcp binding address Syntax Description address Optional Specifies the IP address of the DHCP client for which bindings will be displayed Defaults None Command Modes EXEC Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T If the address is not specified all address bindings are shown Otherwise only the binding for the specified client is displayed Examples The following examples show the DHCP binding address parameters including an IP address an associated MAC address a lease expiration date and the type of address assignment that have occurred Table 2 lists descriptions of the fields in each example Router gt show ip dhcp binding 172 16 1 11 IP address Hardware address Lease expiration Type DPD Orel eT 00a0 9802 32de Feb 01 1998 12 00 AM Automatic Router gt show ip dhcp binding 172 16 3 254
19. address L fe 2 gt m l E 32369 The client returns a formal request for the offered IP address to the DHCP server in a DHCPREQUEST broadcast message The DHCP server confirms that the IP address has been allocated to the client by returning a DHCPACK unicast message to the client Cisco IOS DHCP Server 1 Benefits Benefits Note The formal request for the offered IP address the DHCPREQUEST message that is sent by the client is broadcast so that all other DHCP servers that received the DHCPDISCOVER broadcast message from the client can reclaim the IP addresses that they offered to the client If the configuration parameters sent to the client in the DHCPOFFER unicast message by the DHCP server are invalid a misconfiguration error exists the client returns a DHCPDECLINE broadcast message to the DHCP server The DHCP server will send to the client a DHCPNAK denial broadcast message which means the offered configuration parameters have not been assigned if an error has occurred during the negotiation of the parameters or the client has been slow in responding to the DHCPOFFER message the DHCP server assigned the parameters to another client of the DHCP server The Cisco IOS DHCP Server feature offers the following benefits Reduced Internet access costs Using automatic IP address assignment at each remote site substantially reduces Internet access costs Static IP addresses are
20. aim them when old clients are retired Dynamic Host Configuration Protocol DHCP A protocol that provides a mechanism for allocating IP addresses dynamically so that addresses can be reused when hosts no longer need them manual address allocation An address assignment method that allocates an administratively assigned IP address to a host Manual allocation allows DHCP to be used to eliminate the error prone process of manually configuring hosts with IP addresses server Any host providing configuration parameters 52 Release 12 0 1 T
21. ask of the client The prefix length must be preceded by a forward slash Defaults None Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T This command is valid for DHCP subnetwork address pools only If the mask or prefix length is not specified the class A B or C natural mask is used The DHCP server assumes that all host addresses are available The system administrator can exclude subsets of the address space by using the ip dhcp excluded address command You can not configure manual bindings within the same pool that is configured with the network command Examples The following example configures 172 16 0 0 16 as the DHCP pool s subnetwork number and mask network 172 16 0 0 16 Related Commands host ip dhcp excluded address ip dhcp pool 38 Release 12 0 1 T next server next server To configure the next server in a Dynamic Host Configuration Protocol DHCP client s boot process use the next server DHCP pool configuration command Use the no form of this command to remove the boot server list next server address address2 address8 no next server address Syntax Description address Specifies the IP address of the next server in the boot process which is typically a Trivial File Transfer Protocol TFTP server One IP address is required although you can specify up to eight addresses in one command line Defaults If the n
22. bling DHCP Conflict Logging Configuring a DHCP Database Agent or Disabling DHCP Conflict Logging A DHCP database agent is any host for example an FTP TFTP or RCP server that stores the DHCP bindings database You can configure multiple DHCP database agents and you can configure the interval between database updates and transfers for each agent To configure a database agent and database agent parameters use the following command in global configuration mode Command Purpose Router config ip dhcp database url Configures the database agent and the interval between timeout seconds write delay seconds database updates and database transfers If you choose not to configure a DHCP database agent disable the recording of DHCP address conflicts on the DHCP server To disable DHCP address conflict logging use the following command in global configuration mode Command Purpose Router config no ip dhep conflict Disables DHCP address conflict logging logging Excluding IP Addresses The DHCP server assumes that all IP addresses in a DHCP address pool subnet are available for assigning to DHCP clients You must specify the IP address that the DHCP server should not assign to clients To do so use the following command in global configuration mode Command Purpose Router config ip dhcp Specifies the IP addresses that the DHCP server should not excluded address low address assign to DHCP clients high address
23. clear ip dhcp server statistics Resets all DHCP server counters to 0 To enable DHCP server debugging use the following command in privileged EXEC mode as needed Command Purpose Router debug ip dhcp server events Enables debugging on the DHCP server packets linkage Cisco IOS DHCP Server 9 Configuration Examples To display DHCP server information use the following commands in EXEC mode as needed Command Purpose Router gt show ip dhcp binding address Displays a list of all bindings created on a specific DHCP server Router gt show ip dhcp conflict address Displays a list of all address conflicts recorded by a specific DHCP server Router show ip dhcp database url Displays recent activity on the DHCP database Note Use this command in privileged EXEC mode Router gt show ip dhep server statistics Displays count information about server statistics and mes sages sent and received Configuration Examples This section provides the following configuration examples DHCP Database Agent Configuration Example DHCP Address Pool Configuration Example Manual Bindings Configuration Example DHCP Database Agent Configuration Example The following example stores bindings on host 172 16 4 253 The file transfer protocol is FTP The server should wait 2 minutes 120 seconds before writing database changes ip dhcp database ftp user password 172 16 4 253 router dhcp write delay 120
24. considerably more expensive to purchase than are automatically allocated IP addresses Reduced client configuration tasks and costs Because DHCP is easy to configure it minimizes operational overhead and costs associated with device configuration tasks and eases deployment by nontechnical users Centralized management Because the DHCP server maintains configurations for several subnets an administrator only needs to update a single central server when configuration parameters change Supported Platforms This Cisco IOS DHCP Server feature is supported on the following routers and access servers Catalyst 5000 family switches with an installed Route Switch Module Catalyst 6000 family switches with an installed MultiLayer Switch Feature Card Catalyst 8500 series Cisco 800 series Cisco 1000 series Cisco 1400 series Cisco 1600 series Cisco 1700 series support for the Cisco 1700 series was added in Cisco IOS Release 12 0 2 T Cisco 2500 series Cisco 2600 series Cisco 3600 series Cisco 3800 series 2 Release 12 0 1 T Cisco MC3810 series Cisco 4000 series Cisco AS5100 access server Cisco AS5200 universal access server Cisco AS5300 universal access server Cisco 7000 series Cisco 7100 series Cisco 7200 series Cisco MGX 8800 with an installed Route Processor Module Cisco 12000 series Cisco uBR900 series Cisco uBR7200 series Supported Stan
25. dards MIBs and RFCs Standards No new or modified standards are supported by this feature MIBs No new or modified MIBs are supported by this feature For descriptions of supported MIBs and how to use MIBs see the Cisco MIB web site on CCO at http www cisco com public sw center netmgmt cmtk mibs shtml RFCs RFC 951 Bootstrap Protocol BOOTP RFC 1542 Clarifications and Extensions for the Bootstrap Protocol RFC 2131 Dynamic Host Configuration Protocol RFC 2132 DHCP Options and BOOTP Vendor Extensions Cisco IOS DHCP Server 3 Prerequisites Prerequisites Before you configure the Cisco IOS DHCP Server feature complete the following tasks Identify an external File Transport Protocol FTP Trivial File Transfer Protocol TFTP or remote copy protocol rcp server that you will use to store the DHCP bindings database Identify the IP addresses that you will enable the DHCP server to assign and the IP addresses that you will exclude Identify DHCP options for devices where necessary including Default boot image name Default router s Domain Name System DNS server s NetBIOS name server Decide on a NetBIOS node type b p m or h Decide on a DNS domain name DHCP Configuration Task List The DHCP server database is organized as a tree The root of the tree is the address pool for natural networks branches are subnetwork address pools and leaves are manual bind
26. dropped Command Modes Global configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T This command is used by cable modem termination systems By default DHCP checks relay information Invalid messages are dropped Examples The following example configures the DHCP server to check that the relay agent information option in forwarded BOOTREPLY messages is valid ip dhcp relay information check Related Commands ip dhcp relay information option ip dhcp relay information policy 32 Release 12 0 1 T ip dhcp relay information option ip dhcp relay information option To configure a Cisco IOS Dynamic Host Configuration Protocol DHCP Server to insert the DHCP relay agent information option in forwarded BOOTREQUEST messages use the ip dhcp relay information option global configuration command Use the no form of this command to disable inserting relay information to forwarded BOOTREQUEST messages ip dhcp relay information option no ip dhep relay information option Syntax Description This command has no arguments or keywords Defaults The DHCP server does not insert relay information Command Modes Global configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T This command is used by cable modem termination systems By default DHCP does not insert relay information Examples The following example configures a DHCP server to insert
27. e name Optional Specifies the name of the client using any standard ASCII character The client name should not include the domain name For example the name mars should not be specified as mars cisco com Configuring a DHCP Server Boot File The boot file is used to store the boot image for the client The boot image is generally the operating system the client uses to load To specify a boot file for the DHCP client use the following command in DHCP pool configuration mode Command Purpose Router config dhcp bootfile filename Specifies the name of the file that is used as a boot image Configuring the Number of Ping Packets 8 By default the DHCP server pings a pool address twice before assigning the address to a requesting client If the ping is unanswered the DHCP server assumes with a high probability that the address is not in use and assigns the address to the requesting client To change the number of ping packets the DHCP server should send to the pool address before assigning the address use the following command in global configuration mode Command Purpose Router config ip dhcp ping packets Specifies the number of ping packets the DHCP server sends to number a pool address before assigning the address to a requesting cli ent The default is two packets Release 12 0 1 T Configuring the Timeout Value for Ping Packets Configuring the Timeout Value for Ping Packets By default the DHCP se
28. e second example below shows database linkage information Router debug ip dhcp server events Router debug ip dhcp server packets DHCPD DHCPDISCOVER received from client 0b07 1134 a029 through relay 10 1 0 253 DHCPD assigned IP address 10 1 0 3 to client 0b07 1134 a029 DHCPD Sending DHCPOFFER to client 0b07 1134 a029 10 1 0 3 DHCPD unicasting BOOTREPLY for client 0b07 1134 a029 to relay 10 1 0 253 DHCPD DHCPREQUEST received from client 0b07 1134 a029 DHCPD Sending DHCPACK to client 0b07 1134 a029 10 1 0 3 DHCPD unicasting BOOTREPLY for client 0b07 1134 a029 to relay 10 1 0 253 DHCPD checking for expired leases Router debug ip dhcp server linkage DHCPD child pool 10 1 0 0 255 255 0 0 subnet10 1 DHCPD parent pool 10 0 0 0 255 0 0 0 net10 DHCPD child pool 10 0 0 0 255 0 0 0 net10 DHCPD pool net10 has no parent DHCPD child pool 10 1 0 0 255 255 0 0 subnet10 1 DHCPD parent pool 10 0 0 0 255 0 0 0 net10 DHCPD child pool 10 0 0 0 255 0 0 0 net10 DHCPD pool net10 has no parent Related Commands show ip dhcp bindings show ip dhcp database Cisco IOS DHCP Server 51 Glossary Glossary address binding A mapping between the client s IP and hardware MAC addresses The client s IP address may be configured by the administrator manual address allocation or assigned from a pool by the DHCP server automatic address allocation The binding also contains a lease expiration date The default
29. ecify up to eight addresses in one command line Defaults None Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T The IP address of the router should be on the same subnet as the client subnet You can specify up to eight routers in the list Routers are listed in order of preference address1 is the most preferred router address is the next most preferred router and so on Examples The following example specifies 10 12 1 99 as the IP address of the default router default router 10 12 1 99 Related Commands ip dhcp pool 20 Release 12 0 1 T dns server dns server To specify the Domain Name System DNS IP servers available to a Dynamic Host Configuration Protocol DHCP client use the dns server DHCP pool configuration command Use the no form of this command to remove the DNS server list dns server address address2 address8 no dns server Syntax Description address Specifies the IP address of a DNS server One IP address is required although you can specify up to eight addresses in one command line Defaults If DNS IP servers are not configured for a DHCP client the client cannot correlate host names to IP addresses Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Servers are listed in order of preference address is the most preferred server address2 is the next
30. es This command first appeared in Cisco IOS Release 12 0 1 T The administrator may configure multiple database agents Bindings are transferred by using the File Transfer Protocol FTP Trivial File Transport Protocol TFTP or remote copy protocol RCP Example The following example specifies the DHCP database transfer timeout value at 80 seconds ip dhcp database ftp user password 172 16 1 1 router dhcp timeout 80 The following example specifies the DHCP database update delay value at 100 seconds ip dhcp database tftp 172 16 1 1 router dhcp write delay 100 26 Release 12 0 1 T ip dhcp database Related Commands show ip dhcp database Cisco IOS DHCP Server 27 Command Reference ip dhcp excluded address To specify IP addresses that a Cisco IOS Dynamic Host Configuration Protocol DHCP Server should not assign to DHCP clients use the ip dhcp excluded address global configuration command Use the no form of this command to remove the excluded IP addresses ip dhcp excluded address low address high address no ip dhcp excluded address low address high address Syntax Description low address The excluded IP address or first IP address in an excluded address range high address Optional The last IP address in the excluded address range Defaults All IP pool addresses are assignable Command Modes Global configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T The
31. ext server command is not used to configure a boot server list the DHCP server uses inbound interface helper addresses as boot servers Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T You can specify up to eight servers in the list Servers are listed in order of preference address 1 is the most preferred server address2 is the next most preferred server and so on Examples The following example specifies 10 12 1 99 as the IP address of the next server in the boot process next server 10 12 1 99 Related Commands bootfile ip dhcp pool ip helper address option Cisco IOS DHCP Server 39 Command Reference option To configure Cisco IOS Dynamic Host Configuration Protocol DHCP Server options use the option DHCP pool configuration command Use the no form of this command to remove the options option code instance number ascii string hex string ip address no option code instance number Syntax Description code Specifies the DHCP option code instance number Optional Specifies a number from 0 to 255 ascii string Specifies an NVT ASCII character string ASCII character strings that contain white space must be deliminated by quotation marks hex string Specifies dotted hexadecimal data Each byte in hexidecimal character strings is two hexidecimal digits each byte can be separated by a period colon or white space ip address Speci
32. fies an IP address Defaults The default instance number is 0 Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T DHCP provides a framework for passing configuration information to hosts on a TCP IP network Configuration parameters and other control information are carried in tagged data items that are stored in the options field of the DHCP message The data items themselves are also called options The current set of DHCP options are documented in RFC 2131 Dynamic Host Configuration Protocol Examples The following example configures DHCP option 19 which specifies whether the client should configure its IP layer for packet forwarding A value of 0 means disable IP forwarding a value of 1 means enable IP forwarding IP forwarding is enabled in the following example option 19 hex 01 The following example configures DHCP option 72 which specifies the World Wide Web servers for DHCP clients World Wide Web servers 172 16 3 252 and 172 16 3 253 are configured in the following example option 72 1p 172 163 2592 192 16 3 253 40 Release 12 0 1 T option Related Commands ip dhcp pool Cisco IOS DHCP Server 41 Command Reference service dhcp To enable the Cisco IOS Dynamic Host Configuration Protocol DHCP Server feature on your router use the service dhcp global configuration command Use the no form of this command to disable the Cisco IO
33. hcp excluded address ip dhcp ping packets ip dhcp ping timeout ip dhcp pool ip dhcp relay information check ip dhcp relay information option ip dhcp relay information policy lease netbios name server netbios node type network DHCP next server option service dhcp show ip dhcp binding show ip dhcp conflict show ip dhcp database show ip dhcp server statistics 12 Release 12 0 1 T Manual Bindings Configuration Example In Cisco IOS Release 12 0 1 T or later you can search and filter the output for show and more commands This functionality is useful when you need to sort through large amounts of output or if you want to exclude output that you do not need to see To use this functionality enter a show or more command followed by the pipe character I one of the keywords begin include or exclude and an expression that you want to search or filter on command begin include exclude regular expression Following is an example of the show atm vc command in which you want the command output to begin with the first line where the expression PeakRate appears show atm vc begin PeakRate For more information on the search and filter functionality refer to the Cisco IOS Configuration Fundamentals Configuration Guide Cisco IOS DHCP Server 13 Command Reference bootfile To specify the name of the default boot image for a Dynamic Host C
34. hcp ping packets 5 Related Commands clear ip dhep conflicts ip dhcp ping timeout show ip dhcp conflicts Cisco IOS DHCP Server 29 Command Reference ip dhcp ping timeout To specify how long a Cisco IOS Dynamic Host Configuration Protocol DHCP Server waits for a ping reply from an address pool use the ip dhep ping timeout global configuration command Use the no form of this command to restore the default number of milliseconds 500 of the timeout ip dhcp ping timeout milliseconds no ip dhcp ping timeout Syntax Description milliseconds The amount of time in milliseconds that the DHCP server waits for a ping reply before it stops attempting to reach a pool address for client assignment The maximum timeout is 10000 milliseconds 10 seconds The default timeout is 500 milliseconds Defaults 500 milliseconds Command Modes Global configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T This command specifies how long to wait for a ping reply in milliseconds Examples The following example specifies that the DHCP server will wait 800 milliseconds for a ping reply before considering the ping a failure ip dhcp ping timeout 800 Related Commands clear ip dhep conflicts ip dhep ping packets show ip dhcp conflicts 30 Release 12 0 1 T ip dhcp pool ip dhcp pool To configure a Dynamic Host Configuration Protocol DHCP address pool on a Cisco IOS DHCP Server and e
35. hough you can specify up to eight addresses in one command line Configuring the Address Lease Time By default each IP address assigned by a DHCP server comes with a one day lease which is the amount of time that the address is valid To change the lease value for an IP address use the following command in DHCP pool configuration mode Command Purpose Router config dhcp lease days Specifies the duration of the lease The default is a a one day hours minutes infinite lease Configuring Manual Bindings An address binding is a mapping between the IP address and Media Access Control MAC address of a client The IP address of a client can be assigned manually by an administrator or assigned automatically from a pool by a DHCP server Manual bindings are IP addresses that have been manually mapped to the MAC addresses of hosts that are found in the DHCP database Manual bindings are stored in NVRAM on the DHCP server Manual bindings are just special address pools There is no limit on the number of manual bindings but you can only configure one manual binding per host pool Automatic bindings are IP addresses that have been automatically mapped to the MAC addresses of hosts that are found in the DHCP database Automatic bindings are stored on a remote host called a database agent The bindings are saved as text records for easy maintenance To configure a manual binding first create a host pool then specify the IP addres
36. ings to clients Subnetworks inherit network parameters and clients inherit subnetwork parameters Therefore common parameters for example the domain name should be configured at the highest network or subnetwork level of the tree Note Inherited parameters can be overridden For example if a parameter is defined in both the natural network and a subnetwork the definition of the subnetwork is used Address leases are not inherited If a lease is not specified for an IP address by default the DHCP server assigns a one day lease for the address To configure the Cisco IOS DHCP Server feature first configure a database agent or disable conflict logging then configure IP addresses that the DHCP server should not assign excluded addresses and should assign a pool of available IP addresses to requesting clients These configuration tasks are explained in the following sections Each task in the following list is identified as required or optional Configuring a DHCP Database Agent or Disabling DHCP Conflict Logging Required Excluding IP Addresses Required Configuring a DHCP Address Pool Required Configuring Manual Bindings Optional Configuring a DHCP Server Boot File Optional Configuring the Number of Ping Packets Optional Configuring the Timeout Value for Ping Packets Optional Enabling the Cisco IOS DHCP Server Feature Optional 4 Release 12 0 1 T Configuring a DHCP Database Agent or Disa
37. lease 0 1 The following example shows a one minute lease lease 0 0 1 The following example shows an infinite unlimited lease lease infinite Related Commands ip dhcp pool Cisco IOS DHCP Server 35 Command Reference netbios name server To configure NetBIOS Windows Internet Naming Service WINS name servers that are available to Microsoft Dynamic Host Configuration Protocol DHCP clients use the netbios name server DHCP pool configuration command Use the no form of this command to remove the NetBIOS name server list netbios name server address address2 address8 no netbios name server Syntax Description address Specifies the IP address of the NetBIOS WINS name server Defaults None Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T One IP address is required although you can specify up to eight addresses in one command line Servers are listed in order of preference address is the most preferred server address2 is the next most preferred server and so on Examples The following example specifies the IP address of a NetBIOS name server available to the client netbios name server 10 12 1 90 Related Commands dns server domain name ip dhcp pool netbios node type 36 Release 12 0 1 T netbios node type netbios node type To configure the NetBIOS node type for Microsoft Dynamic Host Configuration Protocol DHCP clie
38. nter DHCP pool configuration mode use the ip dhep pool global configuration command Use the no form of this command to remove the address pool ip dhcp pool name no ip dhcp pool name Syntax Description name Can either be a symbolic string such as engineering or an integer such as 0 Defaults DHCP address pools are not configured Command Modes Global configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T During execution the configuration mode changes to DHCP pool configuration mode identified by the config dhcp prompt In this mode the administrator can configure pool parameters like the IP subnet number and default router list Examples The following example configures pooll as the DHCP address pool ip dhcp pool pooll Related Commands host ip dhcp excluded address network DHCP Cisco IOS DHCP Server 31 Command Reference ip dhcp relay information check To configure a Cisco IOS Dynamic Host Configuration Protocol DHCP Server to validate the relay agent information option in forwarded BOOTREPLY messages use the ip dhcp relay information check global configuration command Use the no form of this command to disable an information check ip dhcp relay information check no ip dhcp relay information check Syntax Description This command has no arguments or keywords Defaults The DHCP server checks relay information Invalid messages are
39. nts use the netbios node type DHCP pool configuration command Use the no form of this command to remove the NetBIOS node type netbios node type type no netbios node type Syntax Description type Specifies the NetBIOS node type Valid types are b node Broadcast e p node Peer to peer m node Mixed h node Hybrid recommended Defaults None Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T The recommended type is h node hybrid Examples The following example specifies the client s NetBIOS type as hybrid netbios node type h node Related Commands ip dhcp pool netbios name server Cisco IOS DHCP Server 37 Command Reference network DHCP To configure the subnet number and mask for a Dynamic Host Configuration Protocol DHCP address pool on a Cisco IOS DHCP Server use the network DHCP pool configuration command Use the no form of this command to remove the subnet number and mask network network number mask prefix length no network Syntax Description network number The IP address of the DHCP address pool mask Optional The bit combination that renders which portion of the address of the DHCP address pool refers to the network or subnet and which part refers to the host prefix length Optional Specifies the number of bits that comprise the address prefix The prefix is an alternative way of specifying the network m
40. onfiguration Protocol DHCP client use the bootfile DHCP pool configuration command Use the no form of this command to delete the boot image name bootfile filename no bootfile Syntax Description filename Specifies the name of the file that is used as a boot image Defaults No default behavior or values Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Examples The following example specifies xllboot as the name of the boot file bootfile xllboot Related Commands ip dhcp pool next server 14 Release 12 0 1 T clear ip dhcp binding clear ip dhcp binding To delete an automatic address binding from the Cisco IOS Dynamic Host Configuration Protocol DHCP Server database use the clear ip dhcp binding privileged EXEC command clear ip dhcp binding address Syntax Description address The address of the binding you want to clear Clears all automatic bindings Command Modes Privileged EXEC Usage Guidelines Typically the address denotes the client s IP address If the asterisk character is used as the address parameter DHCP clears all automatic bindings Use the no ip dhep pool global configuration command to delete a manual binding Examples The following example deletes the address binding 10 12 1 99 from a DHCP server database clear ip dhcp binding 10 12 1 99 Related Commands show ip dhcp binding Cisco IOS DHCP Se
41. ounters are cumulative The counters will be initialized or set to zero with this command Examples The following example resets all DHCP counters to zero clear ip dhcp server statistics Related Commands show ip dhcp server statistics Cisco IOS DHCP Server 17 Command Reference client identifier To specify a Microsoft Dynamic Host Configuration Protocol DHCP client s unique identifier in dotted hexadecimal notation use the client identifier DHCP pool configuration command It is valid for manual bindings only Use the no form of this command to delete the client identifier client identifier unique identifier no client identifier Syntax Description unique identifier The distinct identification of the client in dotted hexadecimal notation for example 01b7 0813 8811 66 Defaults None Command Modes DHCP pool configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Microsoft DHCP clients require client identifiers instead of hardware addresses The client identifier is formed by concatenating the media type and the MAC address For example the Microsoft client identifier for Ethernet address b708 1388 f166 is 01b7 0813 88f1 66 where 01 represents the Ethernet media type For a list of media type codes refer to the Address Resolution Protocol Parameters section of RFC 1700 Assigned Numbers Examples The following example specifies the client identifier for Mac
42. rver 15 Command Reference clear ip dhcp conflict To clear an address conflict from the Cisco IOS Dynamic Host Configuration Protocol DHCP Server database use the clear ip dhcp conflict privileged EXEC command clear ip dhep conflict address Syntax Description address The IP address of the host that contains the conflicting address you want to clear Clears all address conflicts Command Modes Privileged EXEC Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T The server detects conflicts using a ping session The client detects conflicts using gratuitous Address Resolution Protocol ARP If the asterisk character is used as the address parameter DHCP clears all conflicts Examples The following example shows an address conflict of 10 12 1 99 being deleted from the DHCP server database clear ip dhcp conflict 10 12 1 99 Related Commands show ip dhcp conflict 16 Release 12 0 1 T clear ip dhcp server statistics clear ip dhcp server statistics To reset all Cisco IOS Dynamic Host Configuration Protocol DHCP Server counters use the clear ip dhcp server statistics privileged EXEC command clear ip dhep server statistics Syntax Description This command has no arguments or keywords Command Modes Privileged EXEC Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T The show ip dhcp server statistics command displays DHCP counters All c
43. rver waits 500 milliseconds before timing out a ping packet To change the amount of time the server waits use the following command in global configuration mode Command Purpose Router config ip dhep ping timeout Specifies the amount of time the DHCP server must wait milliseconds before timing out a ping packet The default 500 milliseconds Enabling the Cisco IOS DHCP Server Feature By default the Cisco IOS DHCP Server feature is enabled on your router If the feature is disabled use the following command in global configuration mode to reenable the Cisco IOS DHCP Server feature on your router Command Purpose Router config service dhcp Enables the Cisco IOS DHCP Server feature on your router Use the no form of this command to disable the Cisco IOS DHCP Server feature Monitoring and Maintaining the DHCP Server To clear DHCP server variables use the following commands in privileged EXEC mode as needed Command Purpose Router clear ip dhcp binding address Deletes an automatic address binding from the DHCP database Specifying address clears the automatic binding for a specific client IP address whereas specifying asterisk clears all automatic bindings Router clear ip dhcp conflict address Clears an address conflict from the DHCP database Specify ing address clears the conflict for a specific IP address whereas specifying an asterisk clears conflicts for all addresses Router
44. s and hardware address of the client or client identifier The hardware address is the MAC address The client identifier which is required for Microsoft clients instead of hardware addresses is formed by concatenating the media type and the MAC address of the client Refer to the Address Resolution Protocol Parameters section of RFC 1700 Assigned Numbers for a list of media type codes Cisco IOS DHCP Server 7 DHCP Configuration Task List To configure manual bindings use the following commands beginning in global configuration mode Step Command Purpose 1 Router config ip dhcp pool name Creates a name for the a DHCP server address pool and places you in DHCP pool configuration mode identified by the config dhcp prompt 2 Router config dhcp host address mask Specifies the IP address and subnet mask of the prefix length client The prefix length specifies the number of bits that comprise the address prefix The prefix is an alternative way of specifying the network mask of the client The prefix length must be preceded by a forward slash 3 Router config dhcp hardware address Specifies a hardware address for the client hardware address type or Router config dhcp client identifier Specifies the distinct identification of the client in unique identifier dotted hexadecimal notation for example 01b7 0813 8811 66 where 01 represents the Ethernet media type 4 Router config dhcp client nam
45. ss prefix The prefix is an alternative way of specifying the network mask of the client The prefix length must be preceded by a forward slash Note You can not configure manual bindings within the same pool that is configured with the network command To configure manual bindings see the Configuring Manual Bindings section Configuring the Domain Name for the Client The domain name of a DHCP client places the client in the general grouping of networks that make up the domain To configure a domain name string for the client use the following command in DHCP pool configuration mode Command Purpose Router config dhcp domain name Specifies the domain name for the client domain Configuring the Domain Name System IP Servers for the Client DHCP clients query DNS IP servers when they need to correlate host names to IP addresses To configure the DNS IP servers that are available to a DHCP client use the following command in DHCP pool configuration mode Command Purpose Router config dhcp dns server address Specifies the IP address of a DNS server that is available to a address2 address8 DHCP client One IP address is required however you can specify up to eight IP addresses in one command line Configuring the NetBIOS Windows Internet Naming Service IP Servers for the Client Windows Internet Naming Service WINS is aname resolution service that Microsoft DHCP clients use to correlate host names to
46. the pool database the Class A B or C natural mask is used This command is valid for manual bindings only There is no limit on the number of manual bindings but you can only configure one manual binding per host pool Examples The following example specifies 10 12 1 99 as the client s IP address and 255 255 248 0 as the subnet mask host 10 12 16 99 255 0299 02 48 0 Related Commands client identifier hardware address ip dhcp pool network DHCP 24 Release 12 0 1 T ip dhcp conflict logging ip dhcp conflict logging To enable conflict logging on a Cisco IOS Dynamic Host Configuration Protocol DHCP Server use the ip dhep conflict logging global configuration command Use the no form of this command to disable conflict logging ip dhcp conflict logging no ip dhcp conflict logging Syntax Description This command has no arguments or keywords Defaults Conflict logging is enabled Command Modes Global configuration Usage Guidelines This command first appeared in Cisco IOS Release 12 0 1 T Cisco recommends using a DHCP server database agent to store automatic bindings If you decide not to use a DHCP server database agent to store automatic bindings use the no ip dhep conflict logging command to disable the recording of address conflicts By default the Cisco IOS DHCP Server records DHCP address conflicts in a log file Example The following example disables the recording of DHCP address conflicts
47. wing example shows all DHCP server database agent information Table 4 lists descriptions for each field in the example Router show ip dhcp database URL t ftp user password 172 16 4 253 router dhcp Read Dec 01 1997 12 01 AM Written i Never Status Last read succeeded Bindings have been loaded in RAM Delay 300 seconds Timeout 300 seconds Failures 0 Successes T Table 4 show ip dhcp database Field Descriptions Field Description URL Specifies the remote file used to store automatic DHCP bindings Following are the acceptable URL file formats e tftp host filename e ftp user password host filename e rcp user host filename 46 Release 12 0 1 T show ip dhcp database Table 4 show ip dhcp database Field Descriptions continued Field Description Read The last time bindings were read from the file server Written The last time bindings were written to the file server Status Indication of whether the last read or write of host bindings was successful Delay The amount of time to wait before updating the database Timeout The amount of time before the file transfer is aborted Failures The number of failed file transfers Successes The number of successful file transfers Related Commands ip dhcp database Cisco IOS DHCP Server 47 Command Reference show ip dhcp server statistics To display Cisco IOS Dynamic Host Configuration Protocol DHCP Server statistics use
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