Cisco Systems Network Card 32369 User Manual

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)  
DHCPREQUEST (broadcast)  
DHCPACK (unicast)  
DHCP server  
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 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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.  
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO at  
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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
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 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.  
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.  
4
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Configuring a DHCP Database Agent or Disabling 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  
[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  
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  
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).  
Cisco IOS DHCP Server 5  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
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  
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. 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 a name resolution service that Microsoft DHCP clients  
use to correlate host names to 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
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  
address [address2 ... address8]  
Specifies the IP address of the default router for a DHCP 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. The default is a a one-day  
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 address 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
DHCP Configuration Task List  
To configure manual bindings, use the following commands beginning in global configuration mode:  
Step  
1
Command  
Purpose  
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 |  
/prefix-length]  
Specifies the IP address and subnet mask of the  
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  
unique-identifier  
Specifies the distinct identification of the client in  
dotted-hexadecimal notation, for example,  
01b7.0813.8811.66, where 01 represents the  
Ethernet media type.  
4
Router(config-dhcp)# client-name 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  
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  
number  
Specifies the number of ping packets the DHCP server sends to  
a pool address before assigning the address to a requesting cli-  
ent. The default is two packets.  
8
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Configuring the Timeout Value for Ping Packets  
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  
Purpose  
Router(config)# ip dhcp ping timeout  
milliseconds  
Specifies the amount of time the DHCP server must wait  
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# 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 |  
packets | linkage}  
Enables debugging on the DHCP server.  
Cisco IOS DHCP Server 9  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Configuration Examples  
To display DHCP server information, use the following commands in EXEC mode, as needed:  
Command  
Purpose  
Router> show ip dhcp binding [address] Displays a list of all bindings created on a specific DHCP  
server.  
Router> show ip dhcp conflict [address] Displays a list of all address conflicts recorded by a specific  
DHCP server.  
Router# show ip dhcp database [url]  
Router> show ip dhcp server statistics  
Displays recent activity on the DHCP database.  
Note Use this command in privileged EXEC mode.  
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  
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.  
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  
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  
172.16.1.101  
Default routers  
172.16.2.100  
172.16.2.101  
DNS server  
172.16.1.102  
172.16.2.102  
NetBIOS name server  
NetBIOS node type  
172.16.1.103  
172.16.2.103  
h-node  
10  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Manual Bindings Configuration Example  
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  
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.f800.0422 and the IP address of the client is 172.16.2.254.  
ip dhcp pool Mars  
host 172.16.2.254  
hardware-address 02c7.f800.0422 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.f800.0422 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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.  
12  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
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 (|), 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
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  
filename  
Specifies the name of the file that is used as a boot image.  
Defaults  
No default behavior or values.  
Command Modes  
Usage Guidelines  
Examples  
DHCP pool configuration  
This command first appeared in Cisco IOS Release 12.0(1)T.  
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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
Usage Guidelines  
Privileged EXEC  
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 dhcp 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 Server 15  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
The IP address of the host that contains the conflicting address you  
want to clear.  
*
Clears all address conflicts.  
Command Modes  
Usage Guidelines  
Privileged EXEC  
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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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 dhcp server statistics  
Syntax Description  
Command Modes  
Usage Guidelines  
This command has no arguments or keywords.  
Privileged EXEC  
This command first appeared in Cisco IOS Release 12.0(1)T.  
The show ip dhcp server statistics command displays DHCP counters. All counters 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
Usage Guidelines  
DHCP pool configuration  
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 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
Usage Guidelines  
Examples  
DHCP pool configuration  
This command first appeared in Cisco IOS Release 12.0(1)T.  
The following example specifies a string client1 that will be the name of the client:  
client-name client1  
Related Commands  
host  
ip dhcp pool  
Cisco IOS DHCP Server 19  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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 specify up to eight addresses in one command line.  
Defaults  
None  
Command Modes  
Usage Guidelines  
DHCP pool configuration  
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, address2 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
Usage Guidelines  
DHCP pool configuration  
This command first appeared in Cisco IOS Release 12.0(1)T.  
Servers are listed in order of preference (address1 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 domain name server of the  
client:  
dns-server 10.12.1.99  
Related Commands  
domain-name  
ip dhcp pool  
Cisco IOS DHCP Server 21  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
Usage Guidelines  
Examples  
DHCP pool configuration  
This command first appeared in Cisco IOS Release 12.0(1)T.  
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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
type  
Specifies the MAC address of the client’s hardware platform.  
Indicates the protocol of the hardware platform. Strings and values are  
acceptable. The string options are:  
• ethernet  
• ieee802  
The value options are:  
• 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.  
DHCP pool configuration  
Command Modes  
Usage Guidelines  
Examples  
This command first appeared in Cisco IOS Release 12.0(1)T.  
The following example specifies b708.1388.f166 as the MAC address of the client:  
hardware-address b708.1388.f166  
Related Commands  
client-identifier  
host  
ip dhcp pool  
Cisco IOS DHCP Server 23  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
Usage Guidelines  
DHCP pool configuration  
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 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 10.12.1.99 255.255.248.0  
Related Commands  
client-identifier  
hardware-address  
ip dhcp pool  
network (DHCP)  
24  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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 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  
Defaults  
This command has no arguments or keywords.  
Conflict logging is enabled.  
Command Modes  
Usage Guidelines  
Global configuration  
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 dhcp 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:  
no ip dhcp conflict logging  
Related Commands  
clear ip dhcp conflict  
ip dhcp database  
show ip dhcp conflicts  
Cisco IOS DHCP Server 25  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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 url [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:  
• 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.  
Global configuration  
Command Modes  
Usage Guidelines  
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:  
The following example specifies the DHCP database update delay value at 100 seconds:  
26  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
ip dhcp database  
Related Commands  
show ip dhcp database  
Cisco IOS DHCP Server 27  
Download from Www.Somanuals.com. All Manuals Search And Download.  
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.  
Global configuration  
Command Modes  
Usage Guidelines  
This command first appeared in Cisco IOS Release 12.0(1)T.  
The 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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.  
ip dhcp 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  
Usage Guidelines  
Global configuration  
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 dhcp ping packets 5  
Related Commands  
clear ip dhcp conflicts  
ip dhcp ping timeout  
show ip dhcp conflicts  
Cisco IOS DHCP Server 29  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
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  
Usage Guidelines  
Global configuration  
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 dhcp conflicts  
ip dhcp ping packets  
show ip dhcp conflicts  
30  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
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  
Usage Guidelines  
Global configuration  
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 pool1 as the DHCP address pool:  
ip dhcp pool pool1  
Related Commands  
host  
ip dhcp excluded-address  
network (DHCP)  
Cisco IOS DHCP Server 31  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
Defaults  
This command has no arguments or keywords.  
The DHCP server checks relay information. Invalid messages are dropped.  
Global configuration  
Command Modes  
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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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 dhcp relay information option  
Syntax Description  
Defaults  
This command has no arguments or keywords.  
The DHCP server does not insert relay information.  
Global configuration  
Command Modes  
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 the DHCP relay agent information option  
in forwarded BOOTREQUEST messages:  
ip dhcp relay information option  
Related Commands  
ip dhcp relay information check  
ip dhcp relay information policy  
Cisco IOS DHCP Server 33  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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.  
Global configuration  
Command Modes  
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 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 dhcp relay information check  
ip dhcp relay information option  
34  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
Usage Guidelines  
Examples  
DHCP pool configuration  
This command first appeared in Cisco IOS Release 12.0(1)T.  
The following example shows a one-day lease:  
lease 1  
The following example shows a one-hour lease:  
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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
Usage Guidelines  
DHCP pool configuration  
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 (address1 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
netbios-node-type  
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  
Specifies the NetBIOS node type. Valid types are:  
b-node Broadcast  
p-node Peer-to-peer  
m-node Mixed  
h-node Hybrid (recommended)  
Defaults  
None  
Command Modes  
Usage Guidelines  
DHCP pool configuration  
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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
mask  
The IP address of the DHCP address pool.  
(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 mask  
of the client. The prefix length must be preceded by a forward slash (/).  
Defaults  
None  
Command Modes  
Usage Guidelines  
DHCP pool configuration  
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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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 next-server command is not used to configure a boot server list, the DHCP server uses  
inbound interface helper addresses as boot servers.  
Command Modes  
Usage Guidelines  
DHCP pool configuration  
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 (address1 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
ascii string  
(Optional) Specifies a number from 0 to 255.  
Specifies an NVT ASCII character string. ASCII character strings that  
contain white space must be deliminated by quotation marks.  
hex string  
ip address  
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.  
Specifies an IP address.  
Defaults  
The default instance number is 0.  
Command Modes  
Usage Guidelines  
DHCP pool configuration  
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 ip 172.16.3.252 172.16.3.253  
40  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
option  
Related Commands  
ip dhcp pool  
Cisco IOS DHCP Server 41  
Download from Www.Somanuals.com. All Manuals Search And Download.  
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  
Defaults  
This command has no keywords or arguments.  
The feature is enabled.  
Command Modes  
Usage Guidelines  
Examples  
Global configuration  
This command first appeared in Cisco IOS Release 12.0(1)T.  
The following example enables DHCP services on the DHCP server:  
service dhcp  
42  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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  
Usage Guidelines  
EXEC  
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  
Router> show ip dhcp binding 172.16.1.11  
IP address  
172.16.1.11  
Hardware address  
00a0.9802.32de  
Lease expiration  
Feb 01 1998 12:00 AM Automatic  
Type  
Router> show ip dhcp binding 172.16.3.254  
IP address  
172.16.2.254  
Hardware address  
02c7.f800.0422  
Lease expiration  
Infinite  
Type  
Manual  
Table 2  
show ip dhcp Field Descriptions  
Description  
Field  
IP address  
Hardware address  
The IP address of the host as recorded on the DHCP server.  
The MAC address or client identifier of the host as recorded  
on the DHCP server.  
Lease expiration  
Type  
The lease expiration date of the IP address of the host.  
The manner in which the IP address was assigned to the host.  
Cisco IOS DHCP Server 43  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Command Reference  
Related Commands  
clear ip dhcp binding  
44  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
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  
Usage Guidelines  
EXEC  
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 offered that have conflicts with other devices. Table 3 lists descriptions of the fields  
in the example.  
Router> show ip dhcp conflict  
IP address  
172.16.1.32  
172.16.1.64  
Detection Method  
Ping  
Gratuitous ARP  
Detection time  
Feb 16 1998 12:28 PM  
Feb 23 1998 08:12 AM  
Table 3  
show ip dhcp conflict Field Descriptions  
Description  
Field  
IP Address  
Detection Method  
The IP address of the host as recorded on the DHCP server.  
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 dhcp conflict  
ip dhcp ping packets  
ip dhcp ping timeout  
Cisco IOS DHCP Server 45  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
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:  
• 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  
Usage Guidelines  
Examples  
Privileged EXEC  
This command first appeared in Cisco IOS Release 12.0(1)T.  
The following example shows all DHCP server database agent information. Table 4 lists descriptions  
for each field in the example.  
Router# show ip dhcp database  
URL  
Read  
:
:
:
:
:
:
:
Dec 01 1997 12:01 AM  
Never  
Last read succeeded. Bindings have been loaded in RAM.  
300 seconds  
300 seconds  
0
1
Written  
Status  
Delay  
Timeout  
Failures  
Successes :  
Table 4  
show ip dhcp database Field Descriptions  
Description  
Field  
URL  
Specifies the remote file used to store automatic DHCP  
bindings. Following are the acceptable URL file formats:  
• rcp://user@host/filename  
46  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
show ip dhcp database  
Table 4  
show ip dhcp database Field Descriptions (continued)  
Description  
Field  
Read  
The last time bindings were read from the file server.  
Written  
Status  
The last time bindings were written to the file server.  
Indication of whether the last read or write of host bindings  
was successful.  
Delay  
The amount of time to wait before updating the database.  
The amount of time before the file transfer is aborted.  
The number of failed file transfers.  
Timeout  
Failures  
Successes  
The number of successful file transfers.  
Related Commands  
ip dhcp database  
Cisco IOS DHCP Server 47  
Download from Www.Somanuals.com. All Manuals Search And Download.  
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  
Defaults  
This command has no arguments or keywords.  
None  
Command Modes  
Usage Guidelines  
Examples  
EXEC  
This command first appeared in Cisco IOS Release 12.0(1)T.  
the example.  
Router> show ip dhcp server statistics  
Memory usage  
40392  
Address pools  
3
Database agents  
Automatic bindings  
Manual bindings  
Expired bindings  
Malformed messages  
1
190  
1
3
0
Message  
Received  
BOOTREQUEST  
DHCPDISCOVER  
DHCPREQUEST  
DHCPDECLINE  
DHCPRELEASE  
DHCPINFORM  
12  
200  
178  
0
0
0
Message  
Sent  
12  
190  
172  
6
BOOTREPLY  
DHCPOFFER  
DHCPACK  
DHCPNAK  
48  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
show ip dhcp server statistics  
Table 5  
show ip dhcp server statistics Field Descriptions  
Description  
Field  
Memory usage  
Address pools  
The number of bytes of RAM allocated by the DHCP server.  
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  
The number of expired leases.  
Malformed messages  
The number of truncated or corrupted messages that were  
received by the DHCP server.  
Message  
Received  
Sent  
The DHCP message type that was received by the DHCP  
server.  
The number of DHCP messages that were received by the  
DHCP server.  
The number of DHCP messages that were sent by the DHCP  
server.  
Related Commands  
clear ip dhcp server statistics  
Cisco IOS DHCP Server 49  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Debug Commands  
Debug Commands  
This section describes the following new debug command:  
50  
Release 12.0(1)T  
Download from Www.Somanuals.com. All Manuals Search And Download.  
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  
Reports server events, like address assignments and database updates.  
Decodes DHCP receptions and transmissions.  
packets  
linkage  
Displays database linkage information (such as parent-child  
relationships in a radix tree).  
Defaults  
DHCP server debugging is not enabled.  
Usage Guidelines  
Examples  
This command first appeared in Cisco IOS Release 12.0(1)T.  
The first example below shows a combination of DHCP server events and decoded receptions and  
transmissions. The 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
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 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 reclaim 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  
Download from Www.Somanuals.com. All Manuals Search And Download.  

Black Box Network Hardware Hardened VDSL Ethernet Extender User Manual
Black Decker Saw 489051 00 User Manual
Blomberg Refrigerator KQD 1360X User Manual
Brilliant Label Flat Panel Television 532H User Manual
Bryan Boilers Boiler DR250 User Manual
Canon All in One Printer MX472 User Manual
Canon Camera Accessories 3554B002 User Manual
Chamberlain Home Security System CWV1000 User Manual
Cisco Systems IP Phone VG202 User Manual
Cisco Systems Life Jacket UCS C420 User Manual