C H A P T E R  3

Feedback DHCP


Note - This chapter applies to the Sun Network 10GbE Switch 72p product only. DHCP is not supported on the Sun Blade 6000 Ethernet Switched NEM 24p 10GbE, so do not use any of the procedures in this chapter for that product.


DHCP allows dynamic configuration of a host computer. When a DHCP client is turned on, it initially does not have an IP address assigned to it. It issues a broadcast message to any DCHP servers that are on the network. An exchange takes place during which the DHCP server assigns an IP address to the client and tells the client certain key network configuration parameters.

Many ISPs require that their customers use a DHCP client, so the ISP may dynamically assign IP addresses and control other network settings. Another use is for laptop computers connected to more than one network. For example, when a laptop is connected to a network in the office and at home, the laptop need not be manually reconfigured for use in the two different networks. Instead, with a DHCP server on both the office network and the home network and with a DHCP Client in the laptop, this can be achieved easily.


3.1 DHCP Commands

The list of CLI commands for the configuration of DHCP is as follows:

DHCP Client

DHCP Relay

DHCP Server


3.2 DHCP Client

Details for DHCP Client commands.

3.2.1 debug ip dhcp client

Sets the debug level for tracing the DHCP client module. The no form of the command disables the debug level for the DHCP client.


debug ip dhcp client {all | event | packets | errors | bind}


no debug ip dhcp client {all | event | packets | errors | bind}


Syntax Description

all - All trace messages.

event - Trace management messages.

packets - Packets related messages.

errors - Trace error code debug messages.

bind - Trace bind messages.

Mode

Privileged EXEC

Defaults

Debugging is disabled.

Example

SEFOS# debug ip dhcp client all


Related Commands

3.2.2 release

Immediately releases the DHCP lease on the interface specified.


release dhcp [{vlan 1-4094 | interface-type interface-id}]


Syntax Description

vlan - VLAN identifier.

interface-type - Interface type.

interface-id - Interface identifier.

Mode

Privileged EXEC

Defaults

Disabled.

Example

SEFOS# renew dhcp vlan 1

Notes

  • VLAN interface must have an IP address assigned by the DHCP server.
  • If the router interface was not assigned an IP address by the DHCP server, the renew DHCP command fails and displays the following error message:

Interface does not have a DHCP originated address


Related Commands

3.2.3 renew

Immediately renews the DHCP lease for the interface specified.


renew dhcp [{vlan 1-4094 | interface-type interface-id}]


Syntax Description

vlan - VLAN identifier.

interface-type - Interface type.

interface-id - Interface identifier.

Mode

Privileged EXEC

Defaults

Disabled.

Example

SEFOS# renew dhcp vlan 1

Notes

  • VLAN interface must have an IP address assigned by the DHCP server.
  • If the router interface was not assigned an IP address by the DHCP. Server, the renew DHCP command fails and displays the following error message:

Interface does not have a DHCP originated address


Related Commands

3.2.4 show ip dhcp client stats

Displays the DHCP client statistics.


show ip dhcp client stats


Mode

Privileged EXEC

Example

SEFOS# show ip dhcp client stats

 

Dhcp Client Statistics

--------------------------

 

Interface : vlan3

Client IP Address : 0.0.0.0

Client Lease Time : 0

Client Remain Lease Time : 0

Message Statistics

------------------

DHCP DISCOVER : 1

DHCP REQUEST : 0

DHCP DECLINE : 0

DHCP RELEASE : 0

DHCP INFORM : 0

DHCP OFFER : 1


Related Commands


3.3 DHCP Relay

Details for DHCP Relay commands.

3.3.1 service dhcp-relay

Enables the DHCP relay agent in the switch. The no form of the command disables the DHCP relay agent. The relay agent becomes active once it is enabled.


service dhcp-relay


no service dhcp-relay


Mode

Global Configuration

Defaults

Disabled.

Example

SEFOS(config)# service dhcp-relay

Notes

The DHCP server should be disabled before enabling the DHCP relay.


Related Commands

3.3.2 ip dhcp server

Sets the IP address of the DHCP server. The relay agent now starts forwarding the packets (that is, UDP broadcasts including BOOTP) from the client to the specified DHCP server. This command allows to add more than one DHCP server. The no form of the command deletes the DHCP server IP address.


ip dhcp server ip-address


no ip dhcp server ip-address


Syntax Description

ip-address - IP address of the server to which the packets are to be forwarded.

Mode

Global Configuration

Defaults

The IP address is 0.0.0.0 and the status of the DHCP relay servers only is disabled.

Example

SEFOS(config)# ip dhcp server 12.0.0.1

Notes

The relay agent will start forwarding the packets from the client to a specific DHCP server only when the relay agent is in the enabled state.


Related Commands

3.3.3 ip helper-address

Sets the IP address of the DHCP server. The relay agent now starts forwarding the packets (that is, UDP broadcasts including BOOTP) from the client to the specified DHCP server. This command allows to add more than one DHCP server.

This command operates similar to the command ip dhcp server. This command also explicitly enables the DHCP relay and disables the DHCP server.


ip helper-address ip-address


Syntax Description

ip-address - IP address of the server to which the packets are to be forwarded.

Mode

Interface Configuration

Defaults

The IP address is 0.0.0.0 and the status of only the DHCP Relay Servers is disabled.

Example

SEFOS(config-if)# ip helper-address 12.0.0.1

Notes

The relay agent will start forwarding the packets from the client to a specific DHCP server only when the relay agent is in the enabled state.


Related Commands

3.3.4 ip dhcp relay information option

Enables the relay agent to perform any processing related to relay agent Information Options. The agent will insert DHCP relay information in DHCP request messages forwarded to the DHCP server, when the relay information option is enabled. The no form of this command disables the insertion of relay information.


ip dhcp relay information option


no ip dhcp relay information option


Mode

Global Configuration

Can also be executed in the VLAN Interface Configuration for a code base with industry-standard commands.

Defaults

Relay information option is disabled.

Example

SEFOS(config)# ip dhcp relay information option

 

SEFOS(config-if)# ip dhcp relay information option

Notes

Only when enabled, the relay agent does any processing related to relay agent Information Options - like inserting the necessary options while relaying a packet from a client to a server and examining or stripping of options when relaying a packet from a server to a client.


Related Commands

3.3.5 ip dhcp relay circuit-id

Configures circuit-id value for this interface. The no form of the command deletes the circuit-id configuration for this interface.


ip dhcp relay circuit-id 1-2147483647


no ip dhcp relay circuit-id


Syntax Description

circuit-id - Value ranges from 1 to 2147483647.

Mode

Interface Configuration

Example

SEFOS(config-if)# ip dhcp relay circuit-id 1


3.3.6 ip dhcp relay remote-id

Configures the remote-id value for this interface. The no form of the command deletes the remote-id configuration.


ip dhcp relay remote-id name


no ip dhcp relay remote-id


Syntax Description

remote-id - Name of the remote identifier.

Mode

Interface Configuration

Example

SEFOS(config-if)# ip dhcp relay remote-id Aricent


3.3.7 debug ip dhcp relay

Enables the debug level for tracing the DHCP relay module. The no form of the command disables the debug level for tracing the DHCP relay module.


debug ip dhcp relay {all | errors}


no debug ip dhcp relay {all | errors}


Syntax Description

all - All trace messages.

errors - Trace error code debug messages.

Mode

Privileged EXEC

Defaults

Debugging is disabled.

Example

SEFOS# debug ip dhcp relay all


Related Commands

3.3.8 show ip dhcp relay information

Displays the DHCP relay information.


show ip dhcp relay information [vlan 4-1094]


Mode

Privileged EXEC

Example

SEFOS# show ip dhcp relay information

 

Dhcp Relay : Disabled

Dhcp Relay Servers only : Disabled

 

DHCP server : 0.0.0.0

 

Dhcp Relay RAI option : Disabled

Debug Level : 0x1

 

No of Packets inserted RAI option : 0

No of Packets inserted circuit ID suboption : 0

No of Packets inserted remote ID suboption : 0

No of Packets inserted subnet mask suboption : 0

No of Packets dropped : 0

No of Packets which did not inserted RAI option : 0


Related Commands

3.3.9 show dhcp server

Displays the DHCP server information.


show dhcp server


Mode

Privileged EXEC

Example

SEFOS# show dhcp server

 

DHCP server: 40.0.0.4


Related Commands


3.4 DHCP Server

Details of DHCP Server commands.

3.4.1 service dhcp-server

Enables the DHCP server. The no form of this command disables the DHCP server.


service dhcp-server


no service dhcp-server


Mode

Global Configuration

Defaults

Disabled.

Example

SEFOS(config)# service dhcp-server

Notes

DHCP relay must be disabled before enabling the DHCP server.


Related Commands

3.4.2 service dhcp

Enables the DHCP server. The no form of this command disables the DHCP server. This command operates similar to the command service dhcp-server.


service dhcp


no service dhcp


Mode

Global Configuration

Defaults

DHCP server is disabled.

Example

SEFOS(config)# service dhcp

Notes

DHCP Relay must be disabled before enabling the DHCP server.


Related Commands

3.4.3 ip dhcp pool

Creates a DHCP server address pool and places the user in the DHCP pool configuration mode. The no form of the command deletes the DHCP server address pool.


ip dhcp pool index_1-2147483647


no ip dhcp pool index_1-2147483647


Syntax Description

index_1-2147483647 - Pool number.

Mode

Global Configuration

Defaults

Address pools are not created by default.

Example

SEFOS(config)# ip dhcp pool 1

Notes

On execution of this command, the configuration mode changes to DHCP pool configuration mode, identified by the (config-dhcp)# prompt. In this mode, the administrator can configure pool parameters.


Related Commands

3.4.4 ip dhcp next-server

Sets the next boot server in the DHCP server configuration parameters. The no form of this command deletes the next boot server from the DHCP server configuration parameters.


ip dhcp next-server ip-address


no ip dhcp next-server


Syntax Description

ip-address - IP address of the server (TFTP server).

Mode

Global Configuration

Example

SEFOS(config)# ip dhcp next-server 12.0.0.1


Related Commands

3.4.5 ip dhcp bootfile

Defines the name of the boot image file that the DHCP client should download during auto install process. The DHCP server passes this file name to the DHCP client. The no form of this command deletes the specified boot file name and assigns the value of boot file name as None (that is, no file is set as boot image file).


ip dhcp bootfile 63


no ip dhcp bootfile


Syntax Description

bootfile - Name of the boot image file that should be downloaded by the DHCP client.

Mode

Global Configuration

Defaults

None (Null terminated string).

Example

SEFOS(config)# ip dhcp bootfile boot.img


Related Commands

3.4.6 bootfile config-file

Defines the name of the boot image file that the DHCP client should download during auto install process. The DHCP server passes this file name to the DHCP client. The no form of this command deletes the specified boot file name and assigns the value of boot file name as None (that is, no file is set as boot image file).

This command operates similar to the command ip dhcp bootfile.


bootfile config-file 63


no bootfile config-file


Syntax Description

bootfile - Name of the boot image file that should be downloaded by the DHCP client.

Mode

Global Configuration

Defaults

None (Null terminated string).

Example

SEFOS(config)# bootfile config-file boot.img


Related Commands

3.4.7 ip dhcp

Sets the DHCP server parameters such as enabling ICMP echo mechanism or offer-reuse timeout. The no form of this command is used to set the DHCP server parameters like disabling ICMP echo mechanism or server offer-reuse to its default value or removing a bind entry from the server binding table.


ip dhcp {ping packets [count_0-10] | server offer-reuse timeout_1-120}


no ip dhcp {ping packets | server offer-reuse | binding ip-address


Syntax Description

ping packets - Enable icmp echo prior to assigning a pool address. The no form of this command option prevents the server from pinging pool addresses.

The count feature of this parameter allows to set the number of ping packets to be sent from the DHCP server to the pool address before assigning the address to a requesting client.

The pinging of pool addresses is disabled, if the count value is set as 0.

server offer-reuse - The amount of time the DHCP server entity would wait for the DHCP REQUEST from the client before reusing the offer.

binding - The binding option if specified deletes the specified address from binding.

Mode

Global Configuration Mode

Defaults

server offer-reuse - 10

Example

SEFOS(config)# ip dhcp ping packets

Notes

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.


Related Commands

3.4.8 ip dhcp option

Sets the DHCP server options.


ip dhcp option code_1-2147483647 {ascii string | hex hex-string | ip address}


no ip dhcp option code_1-2147483647


Syntax Description

code - Option code.

ascii - ASCII string.

hex - Hexadecimal string.

ip - IP address.

Mode

Global Configuration

Example

SEFOS(config)# ip dhcp option 19 hex d

Notes

  • RFC 2132 provides details about option code to option name mapping and the option length information.
  • The following is the list of supported/configurable DHCP options with their corresponding option length values.
  • Options 19, 20, 27, 29, 30, 31, 34, 36, 39, 46 must have length 1.
  • Options 12, 14, 15, 17, 18, 40, 43, 47, 64, 66, 67 must have length >=1.
  • Option 16 must have minimum length 4 and the value for this option must be an IP address and Option 25 can have a length of 2 and 2*n.
  • Option 68 must have length 4 and the value for this option must be an IP address.
  • Options 1-11, 41, 42, 44, 45, 48, 49, 65, 69, 70-76 must have a length of 4. Value for these options must be an IP address.
  • Options 21, 33 must have minimum length as 8 and 8*n.
  • Options 0, 255, 50-60 are non-configurable options.

Related Commands

3.4.9 network

Sets the network IP address and mask in DHCP server configuration parameters. The no form of the command deletes the network IP address and mask from DHCP server configuration.


network network-IP [ {mask | / prefix-length_1-31}] [end ip]


no network


Syntax Description

network-IP - Network IP address of the DHCP pool.

mask - Subnet mask of the DHCP pool.

prefix-length_1-31 - The number of bits that comprise the address prefix. Prefix is an alternative way of specifying the network mask of the client. The prefix length must be preceded by a forward slash (/).

end ip- End IP address of the pool.

Mode

DHCP Pool Configuration

Example

SEFOS(dhcp-config)# network 20.0.0.0 255.0.0.0 20.0.0.100

Notes

This command is valid for DHCP sub network address pools only.


Related Commands

3.4.10 excluded-address

Creates an excluded pool to prevent DHCP server from assigning certain addresses to DHCP clients. The no form of the command deletes the excluded pool.


excluded-address low-address high-address


no 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 - The last IP address in the excluded address range.

Mode

DHCP Pool Configuration

Example

SEFOS(dhcp-config)# excluded-address 20.0.0.20 20.0.0.30

Notes

The DHCP server assumes that all pool addresses may be assigned to clients. This command is used to exclude a single IP address or a range of IP addresses.

Subnet pool should have been created before creating an excluded pool. This excluded pool should be within the range of the created subnet pool. For example, the excluded pool 20.0.0.20 - 20.0.0.30 created using this command is within the already created subnet pool 20.0.0.0 - 20.0.0.100.


Related Commands

3.4.11 ip dhcp excluded-address

Creates an excluded pool to prevent DHCP server from assigning certain addresses to DHCP clients. The no form of the command deletes the excluded pool.

This command operates similar to the command excluded-address. This command is used to exclude a single IP address or a range of 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 - The last IP address in the excluded address range.

Mode

Global Configuration

Example

SEFOS(config)# ip dhcp excluded-address 20.0.0.20 20.0.0.30

Notes

  • The DHCP server assumes that all pool addresses may be assigned to clients.
  • Subnet pool should have been created before creating an excluded pool. This excluded pool should be within the range of the created subnet pool. For example, the excluded pool 20.0.0.20 - 20.0.0.30 created using this command is within the already created subnet pool 20.0.0.0 - 20.0.0.100.

Related Commands

3.4.12 domain-name

Sets the domain name in the DHCP server configuration parameters. The no form of the command deletes the domain name from the DHCP server configuration parameters.


domain-name domain_63


no domain-name


Syntax Description

domain_63 - Client’s domain name string.

Mode

DHCP Pool Configuration

Example

SEFOS(dhcp-config)# domain-name aricent

Notes

The configuration of this command will take effect only after configuring the network address pool using network command.


Related Commands

3.4.13 dns-server

Specifies the IP address of a DNS server that is available to a DHCP client. The no form of the command deletes the DNS server from the DHCP server configuration parameters.


dns-server ip-address


no dns-server


Mode

DHCP Pool Configuration

Example

SEFOS(dhcp-config)# dns-server 20.0.0.1

Notes

If DNS IP servers are not configured for a DHCP client, the client cannot correlate host names to IP addresses.

The configuration of this command will take effect only after configuring the network address pool using network command.


Related Commands

3.4.14 netbios-name-server

Sets the NetBIOS (WINS) name servers in the DHCP server configuration parameters. The no form of the command deletes the NetBIOS name server from the DHCP configuration parameters.


netbios-name-server ip-address


no netbios-name-server


Mode

DHCP Pool Configuration

Example

SEFOS(dhcp-config)# netbios-name-server 20.0.0.3

Notes

The configuration of this command will take effect only after configuring the network address pool using network command.


Related Commands

3.4.15 netbios-node-type

Sets the NetBIOS node type in the DHCP server configuration parameters. The no form of this command is used to delete the NetBios node type from the DHCP server configuration parameters.

The NetBIOS node type for Microsoft DHCP clients can be one of the four settings: broadcast, peer-to-peer, mixed, or hybrid.


netbios-node-type {0-FF | b-node | h-node | m-node | p-node}


no netbios-node-type


Syntax Description

0-FF - Node type value.

b-node - Broadcast node.

h-node - Hybrid node.

m-node - Mixed node.

p-node - Peer-to-peer node.

Mode

DHCP Pool Configuration

Example

SEFOS(dhcp-config)# netbios-node-type h-node

Notes

  • The recommended type is hybrid node
  • The configuration of this command will take effect only after configuring the network address pool using network command

Related Commands

3.4.16 default-router

Sets the default router in the DHCP server configuration parameters. The no form of the command deletes the default router from the DHCP server configuration parameters.


default-router ip-address


no default-router


Mode

DHCP Pool Configuration

Example

SEFOS(dhcp-config)# default-router 10.23.2.99

Notes

The configuration of this command will take effect only after configuring the network address pool using network command.


Related Commands

3.4.17 option

Sets the pool specific DHCP server option. The no form of the command deletes the pool specific DHCP server option.


option code_1-2147483647 {ascii string | hex hex-string | ip address}


no option code_1-2147483647


Syntax Description

code - Option code.

ascii - ASCII string.

hex - Hexadecimal string.

ip - IP address.

Mode

DHCP Pool Configuration

Example

SEFOS(dhcp-config) # option 19 hex f

Notes

  • RFC 2132 provides details about option code to option name mapping and the option length information.
  • The following is the list of supported/configurable DHCP options with their corresponding option length values.
  • Options 19, 20, 27, 29, 30, 31, 34, 36, 39, 46 must have length 1.
  • Options 12, 14, 15, 17, 18, 40, 43, 47, 64, 66, 67 must have length>=1.
  • Option 16 must have minimum length 4 and the value for this option must be an IP address and Option 25 can have a length of 2 and 2*n.
  • Option 68 must have length 4 and the value for this option must be an IP address.
  • Options 1-11, 41, 42, 44, 45, 48, 49, 65, 69, 70-76 must have a length of 4. Value for these options must be an IP address.
  • Options 21, 33 must have minimum length as 8 and 8*n.
  • Options 0, 255, 50-60 are non-configurable options.
  • Network pool must be configured prior to the execution of this command. Only then the configured option will be visible to the user in the show command output. If the network pool.

Related Commands

3.4.18 lease

Configures the duration of the lease for an IP address that is assigned from SEFOS DHCP server to a DHCP client. The no form of this command restores the default value of 3600 seconds.


lease {days_0-365 [hours_0-23 [minutes_1-59]] | infinite}


no lease


Syntax Description

days - Duration of the lease in number of days.

hours - Number of hours in lease.

minutes - Number of minutes in lease.

infinite - Duration of the lease is unlimited.

Mode

DHCP Pool Configuration

Defaults

3600 seconds.

Example

SEFOS(dhcp-config)# lease 1


Related Commands

3.4.19 utilization threshold

Sets the pool usage threshold value in percentage. If the pool usage reaches this threshold level, a syslog event and an SNMP trap message will be generated. The no form of this command sets pool usage threshold to its default value.


utilization threshold {0-100}


no utilization threshold


Mode

DHCP Pool Configuration

Defaults

75

Example

SEFOS(dhcp-config)# utilization threshold 76


Related Commands

3.4.20 host hardware-type

Specifies the hardware address of a DHCP client and host specific DHCP options. The no form of the command deletes the host option.


host hardware-type type_1-2147483647 client-identifier mac-address option code_1-2147483647 {ascii string | hex hex-string | ip address}


no host hardware-type host-hardware-type_1-2147483647 client-identifier client-mac-address option code_1-2147483647


Syntax Description

type - Host hardware address type.

client-identifier- Host MAC address. The client identifier keyword is not supported.

option - The tag octet of the DHCP option.

ascii - ASCII string.

hex - Hex string.

ip - Host IP address.

Mode

DHCP Pool Configuration

Example

SEFOS(dhcp-config)# host hardware-type 1 client-identifier 00:11:22:33:44:55 option 254 ip 10.0.0.1

Notes

The current valid values are only 0 and 1.


Related Commands

3.4.21 debug ip dhcp server

Enables the debug level for tracing the DHCP server module. The no form of this command disables the debug level for tracing the DHCP server module.


debug ip dhcp server {all | events | packets | errors | bind | linkage}


no debug ip dhcp server {all | events | packets | errors | bind | linkage}


Syntax Description

all - All trace messages.

events - Trace management messages.

packets - Packet related messages.

errors - Trace error code debug messages.

bind -Trace bind messages.

linkage - Database linkage messages.

Mode

Privileged EXEC

Defaults

Debugging is disabled.

Example

SEFOS# debug ip dhcp server all

Notes

 


Related Commands

3.4.22 show ip dhcp server information

Displays the DHCP server information.


show ip dhcp server information


Mode

Privileged EXEC

Example

SEFOS# show ip dhcp server information

DHCP server status : Enable

Send Ping Packets : Disable

Debug level : None

Server Address Reuse Timeout : 5 secs

Next Server Adress : 0.0.0.0

Boot file name : None


Related Commands

3.4.23 show ip dhcp server pools

Displays the DHCP server pools.


show ip dhcp server pools


Mode

Privileged EXEC

Example

SEFOS# show ip dhcp server pools

Pool Id : 1

__________________________________________

Subnet : 12.0.0.0

Subnet Mask : 255.0.0.0

Lease time : 3600 secs

Utilization threshold : 75%

Start Ip : 12.0.0.1

End Ip : 12.255.255.255

Subnet Options

______________

Code : 1, Value : 255.0.0.0


Related Commands

3.4.24 show ip dhcp server binding

Displays the DHCP server binding information.


show ip dhcp server binding


Mode

Privileged EXEC

Example

SEFOS# show ip dhcp server binding

Ip Hw Hw Binding Expire

Address Type Address State Time

------- ---- ------- ------ ------

12.0.0.2 Ethernet 00:02:02:03:04:01 Assigned May 12 13:22:41 2009

Notes

Binding refers to the state of binding. This can be offered, assigned or probing. In offered state offer is sent, but no req has been received from the client. In assigned state the address is assigned to the client. In probing state the address is currently being probed by the DHCP server.


Related Commands

3.4.25 show ip dhcp server statistics

This command displays the DHCP server statistics.


show ip dhcp server statistics


Mode

Privileged EXEC Mode

Example

SEFOS# show ip dhcp server statistics

Address pools : 2

Message Received

------- --------

DHCPDISCOVER 6

DHCPREQUEST 2

DHCPDECLINE 0

DHCPRELEASE 0

DHCPINFORM 0

Message Sent

------- ----

DHCPOFFER 6

DHCPACK 2

DHCPNAK 0


Related Commands

 

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