4.6 Dynamic Host Config Protocol (DHCP) Flashcards
What is DHCP?
A protocol used by hosts to obtain various parameters necessary for the clients to operate in a network
What is an address pool
the range of addresses that can be assigned to requesting hosts.
What is a lease
length of time for which the assignment is valid. It contains the assigned IP address and other information for the client.
What are 4 DHCP options
Domain Name Server (DNS) server address(es)
Default router (or default gateway) address
Windows Internet Name Service (WINS) server addresses
Additional TCP/IP configuration parameters
What is binding
is an association of a MAC address with a specific IP address
What is an interface
The interface that responds to DHCP requests is identified automatically according to the IP address assigned to the interface.
What is the first step in the DHCP client process
Lease Request - The client initializes a limited version of TCP/IP and broadcasts a DHCPDISCOVER packet requesting the location of a DHCP server.
What is the second step in the DHCP Client Process?
Lease offer - All DHCP servers with available IP addresses send DHCPOFFER packets to the client. These include the client’s hardware address, the IP address the server is offering, the subnet mask, the duration of the IP lease, and the IP address of the DHCP server making the offer.
What is the third step in the DHCP Client Process?
Lease selection - The client selects the IP address from the first offer it receives and broadcasts a DHCPREQUEST packet requesting to lease the IP address in that offer.
What is the last step in the DHCP Client Process?
IP Lease Acknowledgement - The DHCP server that made the offer responds and all other DHCP servers withdraw their offers. The IP addressing information is assigned to the client and the offering DHCP server sends a DHCPACK (acknowledgement) packet directly to the client. The client finishes initializing and binding the TCP/IP protocol.
Why would you enable DHCP acroos subnets
Because DHCP leases uses frame-level broadcasts and they don’t pass through routers to other subnets
How do you enable dhcp across subnets
Enable BOOTP (DHCP broadcast) requests through the router. Configure a computer for BOOTP forwarding to request IP information on behalf of other clients.
Describe ARP
Used by hosts to discover the MAC address of a computer from its IP address.
Describe Reverse Address Resolution Protocol (RARP)
Used by a host to discover the IP address of a computer from its MAC address.
Describe Bootstrap Protocol (BOOTP)
Used by a host (such as a diskless workstation) to query a bootstrap computer and receive an IP address assignment. A BOOTP server has a static list of MAC addresses and their corresponding IP addresses.
What is the first step in the DHCP configuration process
Identify an external database agent with a URL.
What is the second step in the DHCP Pre-configuration process
Identify the IP address range to be assigned by the DHCP server
What is the third step in the DHCP Pre-configuration process
Identify DHCP options where necessary.
What is the fourth step in the DHCP Pre-configuration process
Identify the DNS domain name.
What does the command Router(config)#service dhcp do
Enables DHCP features on the router.
What does the command Router(config)#no ip dhcp conflict logging do
Prevents an address from being assigned by the DHCP server.
Router(config)#ip dhcp pool [VLAN_ID]
Configures a DHCP address pool on the specified VLAN
Router(dhcp-config)#network [address] [mask
Sets the network address and subnet mask for a DHCP address pool.
Router(dhcp-config)#domain-name [domain]
Sets the domain name to be delivered to DHCP clients.
Router(dhcp-config)#dns-server [server1_ip] [server2_ip]
Sets the DNS server address to be delivered to DHCP clients
Router(dhcp-config)#default-router [router_ip]
Sets the default router address to be delivered to DHCP clients
Router(dhcp-config)#lease [days]
Sets the lease duration (in days) for a DHCP address pool.
Router(dhcp-config)#host [address] [mask]
Router(dhcp-config)#client-identifier [mac_address]
Manually binds a specific IP address and mask to a host.
Router(config-subif)#ip helper-address [address]
Enables the DHCP relay agent feature.
no ip forward-protocol udp [port]
Controls which broadcast packets and protocols are forwarded by a DHCP relay agent.
Router#show ip dhcp binding
Displays information about each IP address lease.
Router#show ip dhcp pool [pool_name]
Displays information about the DHCP address pools, including the following:
Router#show ip dhcp server statistics
Displays DHCP server statistics.
Router#show ip dhcp conflict
Displays IP addresses with conflicts as well as the method used to identify them:
clear ip dhcp conflict
Clears the address conflict list.
Router#show ip dhcp database
Displays DHCP server database agent information, including the following:
Router#show hosts
Displays the default domain name, the style of name lookup service, a list of name server hosts, and the cached list of hostnames and addresses.
Router(config)#interface vlan 1
Router(config-if)#ip address dhcp
Configures an interface on a Cisco device to get its IP address from the DHCP server
use ip dhcp excluded-address [ip address - ip address
use ip dhcp pool cisco to enter dhcp conifg
to configure dns type ip adress of dns server use dns-server [server ip address]
