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DHCP Statement Hierarchy and Inheritance

DHCP configuration statements are organized hierarchically. Statements at the top of the hierarchy apply to the DHCP server and network, branches contain statements that apply to address pools in a subnetwork, and leaves contain statements that apply to static bindings for individual clients. See Table 1.

The pool and static-binding statements appear at the [edit system services dhcp] hierarchy level. You can include the remaining statements at the following hierarchy levels:

[edit system services dhcp][edit system services dhcp pool][edit system services dhcp static-binding]

Table 1: Pool and Binding Statements

Statement

Description

Hierarchy Level

 pool

Configure a pool of IP addresses for DHCP clients on a subnet. When a client joins the network, the DHCP server dynamically allocates an IP address from this pool.

[edit system services dhcp]

 

 static-binding

Set static bindings for DHCP clients. A static binding is a mapping between a fixed IP address and the client’s MAC address.

To minimize configuration changes, include common configuration statements shown in Table 2 (for example, the domain-name statement) at the highest applicable level of the hierarchy (network or subnetwork). Configuration statements at lower levels of the hierarchy override statements inherited from a higher level. For example, if a statement appears at both the [edit system services dhcp] and [edit system services dhcp pool] hierarchy levels, the value assigned to the statement at the [edit system services dhcp pool] level takes priority.

 

Table 2: Common Configuration Statements

Statement

Description

Hierarchy Level

boot-file

Set the boot filename advertised to clients. The client uses the boot image stored in the boot file to complete configuration.

[edit system services dhcp]

[edit system services dhcp pool]

[edit system services dhcp static-binding]

boot-server

Set the server that contains the boot file.

default-lease-time

Set the default lease time assigned to any client that does not request a specific lease time.

domain-name

Configure the name of the domain in which clients will search for a DHCP server host. This is the default domain name that is appended to hostnames that are not fully qualified.

domain-search

Define a domain search list.

maximum-lease-time

Set the maximum lease time allowed by the server.

name-server

Specify the DNS server that maintains the database of client name to IP address mappings.

option

Configure user-defined DHCP options.

router

Specify IP address for routers on the client’s subnetwork. Routers are listed in order of preference.

server-identifier

Set the IP address of the DHCP server.


Published: 2010-04-26

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