Configuring DHCP Client
DHCP Client Configuration Task list
Obtain an IP address for Ethernet interface
Assigning a DHCP-Server address
Configuring DHCP protocol parameters
Obtain an IP address from the DHCP SERVER for PPP exchanging process
DHCP Client Configuration examples
DHCP (Dynamic Host
Configuration Protocol) protocol provides Network configuration parameters
for the host on the Internet. For details about DHCP, see RFC 2131. Allocating
IP ADDRESS on interface is a major function of DHCP on routers. DHCP protocol
supports 3 IP ADDRESS disbribution mechanisms:
l
Auto
allocation—DHCP server allocates a permanent IP ADDRESS to a client
l
Dynamic
allocation—DHCP server allocates an IP ADDRESS to a client for a period
of time or until the client gives up the right of using this address
l
Manual
allocation—DHCP server managers assign an IP address manually and
transfer this address to a client through DHCP protocol
There are several
DHCP applications. Use DHCP protocol when the following requests exists:
To allocate IP
ADDRESS, traffic and other related resources (such as corresponding gateway),
configure DHCP client.
When an interface
on a router connects to A device on the other end through PPP and another
interface is accessing DHCP, users may obtain an IP address from DHCP SERVER by
DHCPprotocol and allocate that IP address to A device through IPCP.
In exiting router versions,
DHCP clients are only supported on Ethernet interface and DHCP protocol packets
process is supported on all types of interfaces. The function provides the
following advantages:
l Reduce configuration time
l Reduce configuration errors
l
Manage
router interface IP addresses with DHCP SERVER
DHCP protocol is
based on Server/Client structure. Therefore, DHCP-Server and DHCP-Client exists
in a DHCP environment:
DHCP-srever – to allocate and take back DHCP protocol-related resources (such
as IP ADDRESS, leasing time, etc) device
DHCP-Client –
obtain IP ADDRESS and other information from DHCP-Server and used in local
system devices
As mentioned
above, DHCP dynamic allocation requires time:
Leasing
time – a valid period of
time start from an IP ADDRESS resource is allocated by a DHCP-Server. After
this period of time, the corresponding resources is going to be taken back by
DHCP-Server. To reuse the resource, users have to apply for DHCP-Client again.
DHCP Client Configuration Task list
Make sure there is at least
one DHCP server on the network before configuring any DHCP. The next section explains how to use DHCP to execute the following
tasks:
l
Obtain an IP ADDRESS for Ethernet interface
l
Assigning a DHCP-Server address
l
Configuring DHCP protocol parameters
l
Obtain
an IP address from the DHCP SERVER for PPP negotiation process
l
Monitor DHCP
Obtain an IP
address for Ethernet interface
Obtain
an IP ADDRESS by DHCP protocol router on the Ethernet interface and execute the
following Commands on Ethernet interface:
Step |
Command |
Function |
1
. |
ip address dhcp |
To assigning a
DHCP protocol to configure the Ethernet interface IP ADDRESS |
Assigning a DHCP-Server address
If there are
DHCP-Server addresses are already known, users may assign these addresses to
reduce the exchanging time for processing these address. Execute the following
Commands under Global
configuration mode.
Step |
Command |
Function |
1
. |
ip dhcp-server ip-address |
To assign DHCP
SERVER IP ADDRESS |
While in “Obtain
one IP ADDRESS from Ethernet Interface”, the Command is optional .
Configuring DHCP protocol parameters
Adjust the
parameters for DHCP protocol exchange as needed. Execute the following Commands
under Global configuration mode:
Step |
Command |
Function |
1 . |
ip dhcp
client minlease seconds |
To assign the
minimum leasing time |
Step |
Command |
Function |
1 . |
ip dhcp client retransmit
count |
To assign the time
for resending protocol packets |
Step |
Command |
Function |
1 . |
ip dhcp client select seconds |
To assign SELECT
interval |
While in “Obtain
one IP ADDRESS from Ethernet Interface”, the above Command is
optional.
Obtain an IP address from the DHCP SERVER for PPP exchanging process
For detail example, see chapters about “configure PPP”.
View the
DHCP-Server (including manually assigned) information. Execute the following
Command under supervisor mode:
Step |
Command |
Function |
1 . |
show dhcp server |
To display DHCP
SERVER information |
View IP ADDRESS
information. Execute the following Command under supervisor mode:
Step |
Command |
Function |
1 . |
show dhcp lease |
To display IP
ADDRESS resource and related information |
In addition, if users allocate an IP ADDRESS for Ethernet interface with
DHCP protocol, they may view Ethernet by “show interface” Command to make sure whether the IP ADDRESS is success.
DHCP Client Configuration examples
DHCP Client configuration is
shown as follows.
Obtaining an IP
ADDRESS example for Ethernet interface
The following example allocates an IP ADDRESS by DHCP protocol for ethernet1/1interface.
!
interface Ethernet1/1
ip address dhcp