CCENT 6 S01 E24 – Routing: SDM and DHCP Server Configuration Pt.2

  CCENT, Networking, Routers

What is DHCP

  • Dynamic Host Configuration Protocol.
  • Automatically assigns IP addresses to connected hosts
  • Usually assigned for a limited time or as long as actively using it.
  • Can be “Manually Allocated” by MAC Address, so same MAC will always get the same IP.
  • DHCP Servers can be server-based or router based.
    • Router based more reliable, less prone to crashing
    • Server based generally easier and use a GUI, thus server based tend to be common.

DHCP Process

  1. PC sends out a “DHCP Discover” broadcast packet.
  2. DHCP Server will reply with “DHCP Offer” which will contain an IP address.  (Unicast)
  3. The PC will reply with a reply saying it accepts the IP (Unicast).
  4. The server replies with an acknowlegement and allocates the IP (Unicast).

Using the SDM to configure DHCP

Configure -> Additional Tasks

Setting up Command Line (cli)

r1(config)#ip dhcp pool POOL-NAME
r1(dhcp-config)#network 172.30.2.0 255.255.255.0
r1(dhcp-config)#domain-name lab.local
r1(dhcp-config)#dns-server 8.8.8.8
r1(dhcp-config)#default-router 172.30.2.1
r1(dhcp-config)#import all
r1(dhcp-config)#lease 3
r1(dhcp-config)#exit
r1(config)#ip dhcp exclude-addresses 172.30.2.1 172.30.2.19
r1(config)#ip dhcp exclude-addresses 172.30.2.101 172.30.2.254
domain-name: sets the default domain name. If you ping ‘r1’ it will automatically add .lab.local to the end of the host name.
dns-server: define the IP of the dns server
default-router: Same as default gateway.
import all: Grabs the information from the dhcp server and applies it to the server – such as the default gateway and dns servers.
lease: hours minutes seconds
ip dhcp exclude-addresses: by default dhcp will hand out all IPs in the subnet. The ‘exclude’ command reserves

 

 

To refresh the DHCP Address on a Windows PC

C:/> ipconfig /refresh

 

Show the addresses handed out

#show ip dhcp binding

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