[LAB5] Dhcp

[LAB5] Dhcp

In a dynamic IP address scenario, each computer does not set a fixed IP address, but only when the computer is powered on

is assigned an IP address, which is referred to as a DHCP client. assigning IP to DHCP clients

is called a DHCP server. This means that DHCP is in client/server (client/server) mode,

Clear division of client and server roles.

The working process for DHCP is as follows:

1. When the DHCP client starts, the client broadcasts the DHCPDISCOVER message to DHCP in the current subnet

The server requests an IP address.

2. When the DHCP server receives the DHCPDISCOVER message, it will be from the address range for that host

It provides an IP address that has not been assigned and temporarily marks the provided IP address as unavailable. Server to

The DHCPOFFER message is sent back to the host. If the network contains more than one DHCP server, the client can

Can receive several Dhcpoffer messages, the client usually only admits the first dhcpoffer.

3. After the client receives the DHCPOFFER, it sends a message to the server containing the IP provided by the DHCP server

Address of the DHCPREQUEST message. If the client does not receive the DHCPOFFER message and remembers the previous network

Configuration, using the previous network configuration (if the configuration is still within the validity period).

4. The DHCP server sends back a reply to the client that contains the IP address that was originally issued and its allocation scheme

Message (DHCPACK).

5. The client receives the DHCPACK message containing the configuration parameters and uses ARP to check if there is a phase on the network

The same IP address. If the check passes, the client accepts the IP address and its parameters, and if a problem is found, the customer

The machine sends DHCPDecline information to the server and restarts the new configuration process. Server received

DHCPDecline the information, mark the address as unavailable.

6. The DHCP server can only assign that IP address to a DHCP client for a certain amount of time, and the DHCP client must

Update the lease before it expires. After the client's 50% lease time has elapsed, requests are initiated at every time

The DHCP server updates the current lease, and the lease is postponed if the DHCP server answers. If the DHCP server is always

No answer, at 87.5% of the valid lease period, the customer should communicate with any other DHCP server and request

Updates its configuration information. If the client cannot contact all DHCP servers, the lease time is

You must discard the current IP address and resend a DHCPDISCOVER message to start the above IP address obtained

Ride.

7. The client can proactively send a dhcprelease message to the server, releasing the current IP address.

1-DHCP Basic Configuration

R1 (config) #service DHCP//Turn on DHCP service

R1 (config) #no ip dhcp conflict logging//shutdown DHCP conflict log

R1 (config) #ip DHCP pool CCIE//define address pool

R1 (dhcp-config) #network 192.168.1.0/24//dhcp The network and mask to be assigned by the server

R1 (dhcp-config) #domain-name cisco.com//Domain name

R1 (dhcp-config) #default-router 192.168.1.1

Default gateway, this address is the same as the Ethernet port address of the router connected to the corresponding network

R1 (dhcp-config) #netbios-name-server 192.168.1.2//wins Server

R1 (dhcp-config) #dns-server 192.168.1.4//dns Server

R1 (dhcp-config) #option IP 192.168.1.3//tftp Server

R1 (dhcp-config) #lease infinite//definition tenancy (defined here is infinite)

R1 (config) #ip dhcp excluded-address 192.168.1.1 192.168.1.5//excluded address segments

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2-DHCP Relay

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R1: Configuring

R1#sh Run | SE ip dhcp pool

IP DHCP Pool CCNP

Network 192.168.0.0 255.255.255.0

Domain-name lab.com

Default-router 192.168.0.1

Dns-server 192.168.0.1

Lease 0 4

IP DHCP Pool CCIE

Network 192.168.1.0 255.255.255.0

Domain-name lab.com

Default-router 192.168.1.1

Dns-server 192.168.1.1

Lease 0 4

R2:

R2 (config) #int F0/1

R2 (config-if) #ip helper-address 12.1.1.1 \ \ Configure DHCP Relay

R1 run RIP announces 12.1.1.0 and 192.168.0.X

R2 run RIP announces 12.1.1.0 and 192.168.1.X

Client:

R4#sh Run int F0/1

Interface FASTETHERNET0/1

IP address DHCP

No shut

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3-Command Summary

Show ip DHCP pool view information for DHCP address pool

show ip DHCP binding view DHCP address binding condition

show ip DHCP database view DHCP databases

show IP interface Viewing interface information

Debug IP DHCP server events dynamically viewing DHCP servers

Service DHCP to turn on DHCP services

No IP DHCP conflict logging shutdown DHCP conflict log

IP DHCP pool configuration DHCP-assigned address pool

Network and mask to be assigned by the networking DHCP Server

Default-router Default Gateway

Domain-name Domain Name

Netbios-name-server WINS Server

Dns-server Domain Name server

Option-IP FTP server

Lease Configure lease Period

IP DHCP excluded-address exclude address segments

IP helper-address Configuring the address of a DHCP relay

This article from the "Erick" blog, declined to reprint!

[LAB5] Dhcp