DHCP in the network.

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Instructor, PACE-IT Program – Edmonds Community College

Areas of Expertise Industry Certifications

PC Hardware

Network Administration

IT Project Management

Network Design

User Training

IT Troubleshooting

Qualifications Summary

Education

M.B.A., IT Management, Western Governor’s University

B.S., IT Security, Western Governor’s University

Entrepreneur, executive leader, and proven manger with 10+ years of experience turning complex issues into efficient and effective solutions.

Strengths include developing and mentoring diverse workforces, improving processes, analyzing business needs and creating the solutions required— with a focus on technology.

Brian K. Ferrill, M.B.A.

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DHCP in the network.

– Static vs. dynamic IP addressing.

– How DHCP works.

– Components and processes of DHCP.

PACE-IT.

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Static vs. dynamic IP addressing.DHCP in the network.

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Static vs. dynamic IP addressing.

How does a computer know what its IP configuration is?

Most likely, a computer received its IP configuration from a DHCP (Dynamic Host Configuration Protocol) server. Not only did the server give the PC an IP address, but it also told the PC where the default gateway was—and more than likely—how to find a DNS server.

A computer will receive its IP configuration in one of two ways, statically (manually set) or dynamically (through a service like DHCP). Static address assignment works fine for very small and stable networks, but quickly becomes unwieldy and error prone as the network grows.

DHCP in the network.

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Static vs. dynamic IP addressing.

– Static IP addressing.» The administrator assigns an IP number and subnet

mask to each host in the network.• Each network interface that is going to be available

to connect to the network requires this information.» The administrator assigns a default gateway location

and DNS server location to each host in the network.• These are required if access outside of the network is

going to be allowed (default gateway) and human friendly naming conventions are allowed to find network resources (DNS server).

» Each time a change is made (e.g., a new default gateway is established) each IP configuration on each host must be updated.

– Dynamic IP addressing.» The administrator configures a DHCP server to handle

the assigning process, which automates the process.• The DHCP server listens on a specific port for IP

information requests.• Once it receives a request, the DHCP server responds

with the required information.

DHCP in the network.

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How DHCP works.DHCP in the network.

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How DHCP works.

– Typical DHCP process.» Upon boot up, a PC that is configured to request

an IP configuration sends a DHCP discovery packet.

• The discovery packet is sent to the broadcast address: 255.255.255.255:67 (UDP port 67).

» The DHCP server receives the discovery packet and responds with an offer packet.

• The offer packet is sent to the MAC address of the computer using UDP port 68.

» The computer receives the offer packet from the DHCP server and returns a request packet (requesting the proper IP configuration) to the DHCP server.

» Once the DHCP server receives the request packet, it sends back an acknowledgement packet, which contains the required IP configuration information.

» Upon receipt of the acknowledgement packet, the PC changes its IP configuration to reflect the information received.

DHCP in the network.

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Components and process of DHCP.DHCP in the network.

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Components and processes of DHCP.

– Ports used.» PC sends discovery packet to 255.255.255.255:67.» DHCP sends offer packet to the PC’s MAC address on

port 68.

– Address scope.» Administrator configures the IP address range with one

that is available to be handed out.

– Address reservations.» Administrator reserves specific IP addresses to be

handed out to specific MAC addresses. These are used for devices that should always have the same IP address (e.g., servers and routers).

» Allows for these addresses to be changed from a central location instead of having to log in to each device separately.

DHCP in the network.

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Components and processes of DHCP.

– Leases.» Configuration parameters are only good for a specified

amount of time.» Leases are configured by the administrator.

– Options.» Default gateway location.» DNS server addresses (there can be more than one).» Time server addresses.» Many additional options.

– Preferred IP configuration.» A PC can have a preferred IP address.» The administrator can configure the DHCP server to

either honor the preference or ignore it.

DHCP in the network.

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Components and processes of DHCP.

Under the right circumstances, a DHCP server isn’t required to reside on the local network segment.

Broadcast transmissions cannot pass through a router. If there is not a DHCP server on the local network segment, the router can be configured to be a DHCP relay. When a DHCP relay (which can also be called an IP helper) receives a discovery packet from a node, it will forward that packet to the network segment on which the DHCP server resides.

This allows for there to be fewer configured DHCP servers in any given network, reducing the amount of maintenance that an administrator needs to perform.

DHCP in the network.

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What was covered.DHCP in the network.

IP configurations can be static or dynamic. In a static configuration, an administrator supplies all of the required IP information to each device that requires it in a network. In a dynamic configuration, an administrator configures a DHCP server to automatically distribute the required IP configuration information upon request.

Topic

Static vs. dynamic IP addressing.

Summary

A device sends a discovery packet. A DHCP server responds with an offer packet (letting the device know that the DHCP server has the required information). Upon receipt of the offer packet, the device sends a request packet (requesting the proper IP configuration). When the DHCP server gets the request packet, it responds with all of the information in an acknowledgement packet.

How DHCP works.

DHCP uses UDP ports 67 and 68 to provide the IP configuration to a PC. The IP address comes from a scope (range) of addresses configured by the administrator. The administrator can reserve a pool of addresses. Options include: default gateway, DNS servers, time servers, and other options. Addresses are leased and leases expire; however, a device can request the same IP address again. A DHCP relay can be used when a DHCP server doesn’t reside on the local network segment.

Components and processes of DHCP.

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THANK YOU!

This workforce solution was 100 percent funded by a $3 million grant awarded by the U.S. Department of Labor's Employment and Training Administration. The solution was created by the grantee and does not necessarily reflect the official position of the U.S. Department of Labor. The Department of Labor makes no guarantees, warranties, or assurances of any kind, express or implied, with respect to such information, including any information on linked sites and including, but not limited to, accuracy of the information or its completeness, timeliness, usefulness, adequacy, continued availability or ownership. Funded by the Department of Labor, Employment and Training Administration, Grant #TC-23745-12-60-A-53.

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