DHCP Flashcards
What is DHCP?
DHCP (dynamic host configuration protocol) is used for dynamically assigning network addresses to hosts. DHCP operates on a client-server model, where a DHCP server sends configuration information to DHCP clients.
DHCP supports three types of address allocation, what are they?
DHCP supports three mechanisms for IP address allocation:
*Automatic allocation—DHCP assigns a permanent IP address to a client.
*Dynamic allocation—DHCP assigns an IP address to a client for a limited period of time (or until the client explicitly relinquishes the address).
*Manual allocation—The network administrator assigns an IP address to a client and DHCP is used simply to convey the assigned address to the client.
DHCP and its messages are based on what protocol?
DHCP is based on BOOTP (bootstrap protocol), which provides the framework for passing configuration information to hosts on a TCP/IP network. The main advantage of DHCP over BOOTP is that you don’t need to configure MAC addresses of all clients on the DHCP server.
What are the steps DHCP clients and server takes to allocate an ip address?
- The operating system on the host is configured to obtain network configuration via DHCP, so the host, acting as DHCP client, sends a DHCPDISCOVER broadcast message to locate a DHCP server.
- A DHCP server on the local subnet offers configuration parameters, including an IP address, to the client in a DHCPOFFER unicast message.
- The DHCP client returns a formal request for the offered IP address to the server in a DHCPREQUEST broadcast message.
- The DHCP server confirms that the IP address has actually been allocated for use by the client by returning the final DHCPACK unicast message.
What is a DHCP relay agent?
A DHCP relay agent is any host that forwards DHCP packets between DHCP clients and DHCP servers. A DHCP relay agent does more than simply forwarding DHCP packets like a router forwarding IP packets. The relay agent receives DHCP messages and then generates a new DHCP message to send on another interface. The Cisco IOS (Internetwork Operating System) running on Cisco routers includes both DHCP server and relay agent software
How will you configure an IOS router to be a dhcp server?
ip dhcp excluded-address 192.168.1.1 192.168.1.50
!
ip dhcp pool Pool_R1
network 192.168.1.0 255.255.255.0
default-router 192.168.1.1
dns-server 192.168.1.1
What command reports IP addresses assigned and client MAC addresses associated with those addresses?
show ip dhcp binding
What command reports the number of addresses leased so far, along with some other details on current utilization of addresses in the DHCP pool ?
show ip dhcp pool
What command reports the number of DHCP messages of each type received, as well as some other statistics.
show ip dhcp server statistics
How does the dhcp server tries to minimize ip address conflict?
DHCP servers detect such conflicts by pinging the new IP address before assigning it to a client. But there is nothing in the world that can prevent someone from statically configuring an IP address from within the range of addresses used by the DHCP server.
What command can you use to see the ip address conflict in dhcp?
show ip dhcp conflict
The DHCP server avoids assigning the addresses from the list to any clients until the list is manually cleared using the clear ip dhcp conflict command.
What are the ports does DHCP use?
The DHCP employs a connectionless service model, using the User Datagram Protocol (UDP). It is implemented with two UDP port numbers for its operations which are the same as for the BOOTP protocol. UDP port number 67 is the destination port of a server, and UDP port number 68 is used by the client.
What are the phases DHCP goes to?
DHCP operations fall into four phases: server discovery, IP lease offer, IP request, and IP lease acknowledgment. These stages are often abbreviated as DORA for discovery, offer, request, and acknowledgment.
How can you enable DHCP service on an IOS router?
service dhcp
