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Using DHCP

This document describes Nx Networks Dynamic Host Configuration Protocol (DHCP) implementation for both the DHCP client and the DHCP server and includes the following sections:

DHCP Overview

Dynamic Host Configuration Protocol (DHCP) is an Internet standard for passing configuration information, including Internet Protocol (IP) addresses, to hosts on a Transmission Control Protocol/Internet Protocol (TCP/IP) network. DHCP is an extension of the BOOTstrap Protocol (BOOTP) that adds the capability of automatic allocation of reusable network addresses. When you configure your Nx Networks router to use DHCP, you enable dynamic, centralized management of the IP addresses on your local internet so you no longer need to assign and track IP addresses manually.

The Nx Networks DHCP implementation allows a LAN interface to be either a DHCP client or a DHCP server, but not both simultaneously.

The DHCP client obtains its IP address and subnet mask for a router LAN interface from a DHCP server.
The DHCP server provides IP address, subnet mask, default gateway, DNS, and domain name information to DHCP clients.

Auto-Configuration

If there is a DHCP server on the local area network (LAN), when you start your router for the first time, it comes up in DHCP client mode on its first LAN interface. If there is no DHCP server on the LAN, the router assigns itself a fixed IP address (192.168.1.1) for the interface and switches to DHCP server mode.

Configuring DHCP Client

This section outlines the initial steps required to configure DHCP client on your router. After completing these tasks, restart the router for the new configuration to take effect.

: 1. Add a special IP address to your router's LAN interface that a DHCP server can dynamically configure.
: 2. Restart the router to activate the configuration changes.

Assigning a Dynamic IP Address to the LAN Interface

: 1. At the IP Config> prompt enter add address.
: 2. Accept 0 for the LAN network (net) number, or enter any other LAN interface number.
: 3. Accept 0.0.0.0 for the LAN interface's IP address.
: 4. Respond Yes to the prompt that asks if you want to allow dynamic address assignment via DHCP.

IP config> add address
Which net is this address for [0]?
New address [0.0.0.0]?
Allow dynamic address assignment via DHCP(Yes or [No]):yes
Accept default routes from DHCP server(Yes or [No]):

Displaying the DHCP Client Monitoring Prompt

To access the DHCP client monitoring environment, enter the following command at the IP> prompt:

IP>dhcDHCP Client>

DHCP Client Commands

This section describes the DHCP client monitoring commands.

Press Space after you type a command to display the available options for each command. Enter help for information about using the command line interface.

[M] means the command is available at the DHCP Client> prompt.

Table 13 DHCP Client Commands

Command Function

Clear [M] Clears either global counters or the counters on a specified interface.

Exit [M] Returns to the previous prompt level.

Interface [M]] Lists either a summary of information on the router's LAN interfaces configured for dynamic address assignment or detailed information on a specified interface.

Release [M] Releases the IP address lease on the specified interface.

Statistics [M] Lists global statistical information about the DHCP client.

Table 13 DHCP Client Commands
Command	Function
Clear [M]	Clears either global counters or the counters on a specified interface.
Exit [M]	Returns to the previous prompt level.
Interface [M]]	Lists either a summary of information on the router's LAN interfaces configured for dynamic address assignment or detailed information on a specified interface.
Release [M]	Releases the IP address lease on the specified interface.
Statistics [M]	Lists global statistical information about the DHCP client.

Clear [M]

Clears either global counters or the counters on a specified interface.

Syntax: clear

Example: clear

Clearing global counters.

Example: clear 0

Clearing counters for client configured on 0.

Exit [M]

Returns to the previous prompt level.

Syntax: exit

Example: exit

Interface [M]

Displays information on all interfaces that you configured to learn their address dynamically or, if you specified the interface number, displays detailed information on the specified interface.

Syntax: interface

Example: interface

Network Number (CR for summary)?
NetName     IP Address       Mask            ServerId         State
Eth/0       128.185.5.2      255.255.255.0   192.168.111.250  Bound
TKR/0        0.0.0.0          0.0.0.0          255.255.255.255  Selecting

Interfaces that are Bound:

NetName   IP Address						   Bound   Lease   Renewal  Rebind  BroadcastAddr
                       Time    Time    Time     Time

   Eth/0  128.185.5.2  15      1000    500      875     255.255.255.255


Lease Time	Time (in seconds) that the DHCP server offered to the client for leasing the IP address. If not offered, the time defaults to 14,400 seconds (4 hours).
Renewal Time	Time the client must renew its lease with the server that originally offered the lease. If the server does not specify the time, it is set to half of lease time.
Rebind Time	Time the client attempts to contact any server, if it cannot renew its lease in renewing state. If the server does not specify the lease time, rebind time defaults to (0.875 times lease time).

Example: interface 0

NetName    IP Address      Mask         serverId         State

   Eth/0   162.6.0.226     255.255.0.0  162.6.0.20       Bound

Destination address:    162.6.0.20
Requested address:      0.0.0.0
Time since bound:       149
Bad packets received:   0
Discover packets sent:  0
Request packets sent:   0
Decline packets sent:   0
Release packets sent:   0
Active Lease:

    serverId:           162.6.0.20
    Packet Type:        DhcpOffer
    Broadcast Address:  162.6.255.255
    Lease Time:         1802
    Renewal Time:       901
    Rebind Time:        1576
Offered Lease(s):       None


State	Possible states that the client can be in: Bound— Client bound to an IP address. Init— Client in initialization state. Rebinding— Client unable to renew its lease and attempting to contact any server. Init Reboot— Client has just rebooted and interface is disabled. Renewing— Client renewing the lease with the server that offered it. Requesting— Client requesting offered parameters from a particular server. Selecting— Client looking for, accumulating, or selecting an offer from multiple offers.
Packet Type	How the client's address was learned a DHCP offer a BOOTP reply.
BroadcastAddr	Specified by the server. If no address specified, displays zero (0).
Lease Time	The time that the client is allowed to use the address.
Renewal Time	Time interval set by the server or by default from the time the client receives an IP address until the client transitions to the renewal state.
Rebind Time	Time interval set by the server from the time the client receives an IP address until the client transitions to the rebinding state.
Destination address	Address to which the last DHCP packet was sent. May be either a broadcast address or a server ID.
Requested address	Address the client would like to be offered. (The client may remember the previously assigned address.)

Release [M]

Releases the lease.

Syntax: release

Example: release

Statistics [M]

Displays statistics related to the DHCP and IP forwarding process.

Syntax: statistics

Example: statistics

Number of clients:           1
Number of clients bound:     1
Bad packets received:        0
Buffer allocation failures:  0
Memory allocation failures:  0

Input packet overflows:     Net   Count
                            Eth/0  0

Configuring DHCP Server

This section outlines the initial steps required to configure DHCP server. After completing these tasks, restart the router for the new configuration to take effect.

: 1. Display the DHCP server configuration prompt.
: 2. Enable the DHCP server.
: 3. Set DNS, if you want your DHCP server to supply the DNS location to DHCP clients.
: 4. Set domain name, if you want your DHCP server to supply the domain name.
: 5. Restart the router to activate the configuration changes.

Notes:

Assignable-Range, Subnet Mask, and Default Gateway are automatically set based on the IP address assigned to the interface.
You must configure a numbered IP address on the selected interface.
OpenROUTE software supports a DHCP server only on LAN interfaces.
You configure a DHCP server per interface. If you have more than one LAN interface, you need to provide the interface number when configuring the server.

Displaying the DHCP Server Configuration Prompt

To access the DHCP server configuration environment, enter the dhs command at the IP Config> prompt:

IP config>dhsDHCP Server Config>

Displaying the DHCP Server Monitoring Prompt

To access the DHCP server monitoring environment, enter the dhs command at the IP> prompt:

IP>dhsDHCP Server>

DHCP Server Commands

This section describes the configuration and monitoring commands for a DHCP server.

Press Space twice after you type a command to display the available options for each command. Enter help for information about using the command line interface.

[C] means the command is available at the DHCP Server config> prompt.

[M] means the command is available at the DHCP Server> prompt.

Table 14 DHCP Server Commands

Command Function

Add [C] [M] Adds a fixed IP address assignment or an interface address range.

Clear-All [C] Modifies information that you originally entered with the add and set commands.

Delete [C] [M] Deletes DHCP configuration information that you entered with the add command.

Disable [C] [M] Disables a DHCP interface.

Enable [C] [M] Enables a DHCP interface.

Exit [C] [M] Returns to the previous prompt.

Free [C] [M] Frees up an individual DHCP IP address assignment or all DHCP IP address assignments. (Should rarely be needed.)

List [C] [M] Lists configuration settings for a selected DHCP interface, a range of fixed or dynamic IP addresses, profile options, or non-assignable IP addresses.

Revert [M]] Restores the configuration that is in permanent memory to the run-time configuration..

Save [M] Saves the current (running) configuration to permanent memory.

Set [C] [M] Sets the configurable DHCP server parameters for the router.

Table 14 DHCP Server Commands
Command	Function
Add [C] [M]	Adds a fixed IP address assignment or an interface address range.
Clear-All [C]	Modifies information that you originally entered with the add and set commands.
Delete [C] [M]	Deletes DHCP configuration information that you entered with the add command.
Disable [C] [M]	Disables a DHCP interface.
Enable [C] [M]	Enables a DHCP interface.
Exit [C] [M]	Returns to the previous prompt.
Free [C] [M]	Frees up an individual DHCP IP address assignment or all DHCP IP address assignments. (Should rarely be needed.)
List [C] [M]	Lists configuration settings for a selected DHCP interface, a range of fixed or dynamic IP addresses, profile options, or non-assignable IP addresses.
Revert [M]]	Restores the configuration that is in permanent memory to the run-time configuration..
Save [M]	Saves the current (running) configuration to permanent memory.
Set [C] [M]	Sets the configurable DHCP server parameters for the router.

Notes:

Changes you make at the Config> prompt do not take effect until you restart the router or enter revert at the DHCP Server> prompt.
Changes you make at the DHCP Server> prompt take effect immediately but do not survive a router restart unless you enter the save command first.
If you add a non-assignable range at the DHCP Server> prompt that includes currently bound addresses, the leases in that range are freed immediately and each client is assigned a new IP address when the original lease expires on the client.
To reset an IP address type parameter back to the automatic value, enter 0.0.0.0.

Add [C] [M]

Adds a fixed IP address or a non-assignable IP address range on an interface.

Syntax: add

fixed-assignment
non-assignable-range

fixed-assignment interface-number

Adds a fixed IP address that the DHCP server assigns to a specified client. The specified IP address is permanently reserved for assignment to the machine with the specified MAC address and is not assigned to any other machine.

Example: add fixed-assignment

Interface [0]?
IP Address? 128.185.10.16
MAC Address? 000093B40014

Note: If you have already configured a fixed IP address, the address you entered overwrites the MAC address.

non-assignable-range interface number

Defines a range of IP addresses that the DHCP server never assigns to any clients.

Example: add non-assignable-range 0

First address of range [0.0.0.0] ?128.185.4.10
Last address of range [0.0.0.0] ?128.185.4.15

Note: IP address range must be a valid range in the same class network.

Clear-All [C]

Clears all configuration settings for the DHCP server.

Syntax: clear-all

Example: clear-all

Are you sure you want to delete all DHCP Server configuration (Yes or [No])?

Delete [C] [M]

Deletes fixed IP address assignments and non-assignable IP address ranges.

Syntax: delete

fixed-assignment
non-assignable-range

fixed-assignment interface-number

Example: delete fixed-assignment

Interface [0]?
IP Address? 128.185.10.16

non-assignable-range interface-number

Example: delete non-assignable-range

Interface [0]?
First address of range [0.0.0.0] ?128.185.5.10
Last  address of range [0.0.0.0] ?128.185.5.15

Disable [C] [M]

Disables the DHCP server on the specified interface. (Turns the server off.)

Syntax: disable interface number

Example: disable

Interface [0]?
Free your run-time in-memory config(Yes or [No]): yes

Notes:

If you are not changing subnets while disabled, you do not need to free your leases.
If the disable time is longer than the lease time for bound IP addresses, you should free your leases.

Enable [C] [M]

Enables the DHCP server on the specified interface. (Turns the server on.)

This command by itself is sufficient to get the DHCP server going. The server derives default settings from the IP address configuration on the interface. However, the specified interface must have a fixed IP address configured.

Syntax: enable interface number

Example: enable 0

Exit [C] [M]

Returns to the previous prompt.

Example: exit

IP Config>

IP>

Free [C] [M]

Frees up the lease(es) that the DHCP server has dynamically assigned.

Syntax: free

all-dynamic-assignments
one-dynamic assignment

all-dynamic-assignments interface number

Frees up all the leases dynamically assigned to the interface.

Example: free all-dynamic-assignments 0

one-dynamic-assignment interface number

Frees up the lease dynamically assigned to a particular IP address.

Example: free one-dynamic-assignment 0

IP address?128.185.11.17

List [C] [M]

Lists either all or pieces of the DHCP server configuration settings.

Syntax: list

all
dynamic-assignment
fixed-assignment
interfaces
non-assignable-range
profile-options
exit

all interface number

Lists the DHCP server's entire configuration for a specified interface.

Example: DHCP Server config>list all

Interface [5]?

Ifc State      Assignable-IP-Address-Range 
5   enabled   *0.0.0.0-0.0.0.0 (*=automatically derived)
 
Option Profile: (*=automatically derived)
Subnet Mask:     *255.255.0.0
Default Gateway: *162.6.0.34
DNS1:             162.6.0.2
DNS2:             0.0.0.0
DNS3:             0.0.0.0
Domain Name:      nxnetworks
Lease Time:       360 seconds

Dynamic assignments:
IP Address      MAC Address   State       BoundTime   LeaseTime
162.6.0.1       000093B40014  Bound       0           360

Example: DHCP Server>list all

Ifc State     ClientsBound   ServerId      Assignable-IP-Address-Range
0   enabled   2             *162.6.0.2    *162.6.0.1-162.2.255.254

Option Profile (*=automatically derived):
Subnet Mask:     *255.255.255.0
Default Gateway: *10.10.1.237
DNS1:             0.0.0.0
DNS2:             0.0.0.0
DNS3:             0.0.0.0
Domain Name:      <none>
Lease Time:       14400 seconds

Non-assignable IP address ranges:
0.0.0.0-0.0.0.0

Dynamic assignments:
IP Address      MAC Address   State       BoundTime   LeaseTime
10.10.1.1       000093B4003C  Bound       4137        14400
10.10.1.2       000093B8A878  Bound       2877        14400


State	The server lease can be in one of the following states: Bound— Lease accepted by client. Init— Lease not offered to any client. Offered— Lease offered to a client. Preoffer— Lease chosen for a particular client, but server waits to be sure there is no other client with the same address on the same subnet

dynamic-assignment interface number

Lists any IP address(es) dynamically assigned to the selected interface.

Example: list dynamic-assignment

Interface [5]?

Dynamic assignments:
IP Address      MAC Address   State       BoundTime   LeaseTime
162.6.0.1       000093B40014  Bound       0           360

fixed-assignment interface number

Lists any fixed IP addresses assigned to the selected interface.

Example: list fixed-assignment

Interface [0]?
Fixed assignments:
IP Address      MAC Address      State      BoundTime   LeaseTime
128.185.10.5    000093B40014     Bound      187         300

interfaces

Lists the DHCP server configuration for the router's interfaces.

Example: DHCP Server Config>list interfaces

Ifc State     Assignable-IP-Address-Range (*=automatically derived)
0   disabled *0.0.0.0-0.0.0.0 
5   enabled  *0.0.0.0-0.0.0.0

Example: DHCP Server>list interfaces

Ifc  State     ClientsBound  ServerId       Assignable-IP-Address-Range
0   enabled-but interface has no fixed IP address-no run-time config
5    enabled   0             *162.6.0.34   *162.6.0.1 - 162.6.255.254

non-assignable-range interface number

Lists any range of IP addresses that the DHCP server cannot dynamically assign.

Example: list non-assignable-range

Interface [5]?
Non-assignable IP address ranges:
128.185.10.10          128.185.10.15

profile-options

Example: list profile options

Interface [5]?
Option Profile (*=automatically derived):  
Subnet Mask:     *255.255.0.0
Default Gateway: *162.6.0.34
DNS1:             162.6.0.2
DNS2:             0.0.0.0
DNS3:             0.0.0.0
Domain Name:      nxnetworks
Lease Time:       360 seconds

Revert [M]

Restores the router's configuration that is in permanent memory.

Syntax: revert interface number

Example: revert

Interface [5]?

Save [M]

Saves the running configuration to permanent memory.

Syntax: save

Example: save

Interface [5]?

Set [C] [M]

Sets certain parameters within your DHCP server configuration.

Syntax: set

assignable-range ([C] only)
default-gateway
dns
domain-name
lease-time
subnet-mask

assignable-range interface number

Sets the range of IP addresses that the DHCP server can assign automatically. (This option is not available in monitor mode [M].)

In most situations, you do not need to explicitly set this option. The DHCP server automatically sets the assignable-range to the full range of IP addresses of the subnet mask specified on the router's interface on which the server is running.

Example: set assignable-range

First address of range [0.0.0.0]? 128.185.19.1
Last address of range [0.0.0.0]? 128.185.19.5

default-gateway interface number

Sets the default gateway mask that the DHCP server assigns automatically.

In most situations, you do not need to explicitly set this option. The DHCP server automatically sets the default gateway value to be the same as the IP address on the router's interface on which the server is running.

Example: set default-gateway 0

Default Gateway (0.0.0.0 = automatic default) [0.0.0.0]?

dns interface number

Sets the Domain Name System (DNS) IP Addresses option that the DHCP server assigns. There is no default value.

Example: set dns 0

DNS1 (0.0.0.0 = none) [0.0.0.0]? 128.185.7.8

domain-name interface number

Sets the domain name option that the DHCP server assigns. There is no default value.

Example: set domain-name 0

Domain name? boston

lease-time interface number

Sets the lease time that the DHCP server assigns to a client.

Example: set lease-time 0

lease time [14400]? 3600

subnet-mask interface number

Sets the subnet mask that the DHCP server assigns automatically.

In most situations, you do not need to explicitly set this option. The DHCP server automatically defaults the subnet mask value to be the same as the IP subnet mask on the router's LAN interface on which the server is running.

Example: set subnet-mask 0

Subnet Mask (0.0.0.0 = automatic default) [0.0.0.0]?

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