Cisco 32369 Manual

Ios dhcp server feature

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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)

Cisco IOS

Host A

DHCPOFFER (unicast)

DHCP server

DHCPREQUEST (broadcast)

DHCPACK (unicast)

A DHCP client may receive offers from multiple DHCP servers and can accept any one of the

Note

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 address.

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

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Summary of Contents for Cisco 32369

Page 1: Feature Overview
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.
Page 2: Supported Platforms
Benefits The formal request for the offered IP address (the DHCPREQUEST message) that is sent by Note 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.
Page 3 • 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 •...
Page 4 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. •...
Page 5 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.
Page 6 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 Router(conﬁg-dhcp)# network...
Page 7 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 Router(conﬁg-dhcp)# netbios-node-type type...
Page 8 DHCP Configuration Task List To conﬁgure manual bindings, use the following commands beginning in global conﬁguration mode: Step Command Router(conﬁg)# ip dhcp pool name Router(conﬁg-dhcp)# host address [mask | /preﬁx-length] Router(conﬁg-dhcp)# hardware-address hardware-address type Router(conﬁg-dhcp)# client-identiﬁer unique-identiﬁer Router(conﬁg-dhcp)# client-name name Configuring a DHCP Server Boot File The boot ﬁle is used to store the boot image for the client.
Page 9 Conﬁguring the Timeout Value for Ping Packets By default, the DHCP server 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 Router(conﬁg)# ip dhcp ping timeout milliseconds Enabling the Cisco IOS DHCP Server Feature By default, the Cisco IOS DHCP Server feature is enabled on your router.
Page 10 Configuration Examples To display DHCP server information, use the following commands in EXEC mode, as needed: Command Router> show ip dhcp binding [address] Router> show ip dhcp conﬂict [address] Router# show ip dhcp database [url] Router> show ip dhcp server statistics Conﬁguration Examples This section provides the following conﬁguration examples: •...
Page 11 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 172.16.1.103 172.16.2.103 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...
Page 12: Command Reference
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 • clear ip dhcp binding • clear ip dhcp conﬂict •...
Page 13 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”...
Page 14 Command Reference bootﬁle To specify the name of the default boot image for a Dynamic Host Configuration 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...
Page 15: 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 Command Modes Privileged EXEC Usage Guidelines...
Page 16 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 dhcp conﬂict address | * Syntax Description address Command Modes Privileged EXEC...
Page 17 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 dhcp server statistics Syntax Description This command has no arguments or keywords. Command Modes Privileged EXEC Usage Guidelines...
Page 18 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...
Page 19 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...
Page 20 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...
Page 21 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...
Page 22 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 Defaults None.
Page 23 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...
Page 24 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 | no host Syntax Description...
Page 25 ip dhcp conﬂict logging To enable conﬂict logging on a Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server, use the ip dhcp 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.
Page 26 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.
Page 27 ip dhcp database Related Commands show ip dhcp database Cisco IOS DHCP Server 27...
Page 28 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...
Page 29: 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 dhcp ping packets global conﬁguration command. Use the no form of this command to prevent the server from pinging pool addresses.
Page 30 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 dhcp 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...
Page 31: Ip Dhcp Pool
ip dhcp pool To conﬁgure a Dynamic Host Configuration Protocol (DHCP) address pool on a Cisco IOS DHCP Server and enter DHCP pool conﬁguration mode, use the ip dhcp 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...
Page 32: Ip Dhcp Relay Information Check
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.
Page 33: 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.
Page 34 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.
Page 35 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...
Page 36 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.
Page 37 netbios-node-type To conﬁgure the NetBIOS node type for Microsoft Dynamic Host Configuration Protocol (DHCP) clients, 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 Defaults None...
Page 38 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 | no network Syntax Description...
Page 39 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 Defaults...
Page 40 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...
Page 41 option Related Commands ip dhcp pool Cisco IOS DHCP Server 41...
Page 42: Service Dhcp
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 IOS DHCP Server feature. service dhcp no service dhcp Syntax Description...
Page 43: 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 Defaults None Command Modes EXEC Usage Guidelines This command ﬁrst appeared in Cisco IOS Release 12.0(1)T.
Page 44 Command Reference Related Commands clear ip dhcp binding Release 12.0(1)T...
Page 45 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 Defaults None...
Page 46: Syntax Description
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 Defaults If a URL is not speciﬁed, all database agent records are shown. Otherwise, only information about the speciﬁed agent is displayed.
Page 47: Related Commands
Table 4 Field Read Written Status Delay Timeout Failures Successes Related Commands ip dhcp database show ip dhcp database Field Descriptions (continued) Description The last time bindings were read from the ﬁle server. The last time bindings were written to the ﬁle server. Indication of whether the last read or write of host bindings was successful.
Page 48: Show Ip Dhcp Server Statistics
Command Reference show ip dhcp server statistics To display Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server statistics, use 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...
Page 49 Table 5 Field Memory usage Address pools Database agents Automatic bindings Manual bindings Expired bindings Malformed messages Message Received Sent Related Commands clear ip dhcp server statistics show ip dhcp server statistics Field Descriptions Description The number of bytes of RAM allocated by the DHCP server. The number of conﬁgured address pools in the DHCP database.
Page 50: Debug Commands
Debug Commands Debug Commands This section describes the following new debug command: • debug ip dhcp server Release 12.0(1)T...
Page 51: 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...
Page 52 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.

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