www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t1/easyip2.htm#xtocid432226
T) * Cisco 2500 series * Cisco 2600 series * Cisco 3600 series * Cisco 3800 series * 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 Standards, 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. 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 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. 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 bindings 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. For example, if a parameter is defined in both the natural network and a subnetwork, the definition of the subnetwork is used. 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. 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 timeout seconds | write-delay seconds Configures the database agent and the interval between 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 dhcp conflict logging Disables DHCP address conflict 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 excluded-address low-address high-address Specifies the IP addresses that the DHCP server should not assign to DHCP clients. 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 dhcp 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). 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 network-number mask | /prefix-length Specifies the subnet network number and mask of the DHCP address pool. 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. Note You can not configure manual bindings within the same pool that is configured with the network command. To configure manual bindings, see the 269 "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 domain Specifies the domain name for the client. 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. Configuring the NetBIOS Windows Internet Naming Service IP Servers for the Client Windows Internet Naming Service (WINS) is a name resolution service that Microsoft DHCP clients use to correlate host names to IP addresses within a general grouping of networks. 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 type Specifies the NetBIOS node type for a Microsoft DHCP client. 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. One IP address is required, although 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 hours minutes | infinite} Specifies the duration of the 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. 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 address and hardware address of the client or client identifier. 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. To configure manual bindings, use ...
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