MCSE 05 Implementing of a Network Infrastructure 03 Theory

8/6/2019 MCSE 05 Implementing of a Network Infrastructure 03 Theory

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Dynamic Host Configuration

Protocol


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Simplifies problems associated with manual addressing Automates

Assigning DHCP of Ips

Tracking Ips

Reassigning IPs DHCP

DHCPDHCP


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Came about as a result of challenges relating to configuringTCP/IP on large Networks

Reverse Address Resolution Protocol (RARP)

Designed for diskless workstations with no means ofpermanently storing TCP/IP settings

Broadcast the MAC address to discover thecorresponding IP address

History of DHCPHistory of DHCP


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Address Resolution Protocol (ARP)

Opposite ofRARP

Broadcast an IP address to discover the

corresponding MAC address.

Medium Access Control (MAC) address- an addressunique to a piece of hardware

History of DHCPHistory of DHCP


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Failed to provide much-needed settings to the client, suchas:

subnet mask

Default gateway

Gave way to the Bootstrap Protocol (BOOTP)

BOOTP enables a TCP/IP workstation to retrieve

settings for all the configuration parameters it needsto run, including an IP address, subnet mask, default

gateway, and Domain Name System (DNS) server

addresses

Disadvantages ofRARPDisadvantages ofRARP


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Using Trivial File Transfer Protocol (TFTP), a workstationcan download an executable boot file from a BOOTP server

Disadvantage is that an administrator must specify settings

for each workstation on the BOOTP server

BOOTP


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DHCP is based heavily on BOOTP, but rather than pushpreconfigured parameters to expected clients, DHCP can

dynamically allocate an IP address from a pool of

addresses and then reclaim it when it is no longer needed

DHCP is an open, industry-standard protocol that reduces

the complexity of administering networks based on TCP/IP

DHCP and BOOTPDHCP and BOOTP


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Centralized administration of IP configuration

DHCP IP configuration information can be stored in onelocation and enables the administrator to centrallymanage all IP configuration information.

A DHCP server tracks all leased and reserved IPaddresses and lists them in the DHCP console, whichshows all DHCP-enabled devices on the network

DHCP Benefits Network AdministratorsDHCP Benefits Network Administrators


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Dynamic host configuration DHCP automates the host configuration process for key

configuration parameters.

This eliminates the need to manually configure individualhosts when TCP/IP is first deployed or when IP

infrastructure changes are required


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Seamless IP host configuration

Use of DHCP ensures that without user interventionDHCP clients get accurate and timely IP configurationparameters, such as the IP address, subnet mask,

default gateway, IP address of the DNS server, etc.

Because the configuration is automatic, troubleshootingof misconfigurations such as mistyped numbers iseliminated


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Flexibility Easy to change IP configurations when the infrastructure

changes

Scalability DHCP scales from small to large networks

Can service networks with 10 clients as well as networks

with thousands of clients


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Core function is to assign addresses

Address allocation is done by clients sending application

layer messages to the server and receiving application

layer messages from the DHCP server

All DHCP messages are carried in User Datagram

Protocol (UDP). Datagrams use port 67 at the server

and 68 at the client.

How DHCP WorksHow DHCP Works


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Configuring Reliability and Redundancy

LONLON--DCDC--0101

DHCP ServerDHCP Server

192.168.16.2/20192.168.16.2/20

NYNY--DCDC--0101

DHCP ServerDHCP Server

192.168.80.2/20192.168.80.2/20

Scope 1Scope 1

192.168.16.1 to192.168.16.1 to

192.168.28.254 (80%)192.168.28.254 (80%)

Scope 2Scope 2

192.168.93.1 to192.168.93.1 to

192.168.95.254 (20%)192.168.95.254 (20%)

Scope 1Scope 1

192.168.80.1 to192.168.80.1 to

192.168.92.254 (80%)192.168.92.254 (80%)

Scope 2Scope 2

192.168.29.1 to192.168.29.1 to

192.168.31.254 (20%)192.168.31.254 (20%)

192.168.16.3192.168.16.3 192.168.29.1192.168.29.1

WorkstationsWorkstations

RoutersRouters192.168.16.1192.168.16.1 192.168.80.1192.168.80.1

HubsHubs

Wide AreaWide Area

NetworkNetwork

WRKWRK--LONLON--001001needs an IPneeds an IP

addressaddress

WRKWRK--LONLON--001001

LeasingLeasing

192.168.16.3 to192.168.16.3 to




needs an IPneeds an IP

addressaddress

X

LeasingLeasing

192.168.29.1 to192.168.29.1 to



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DHCP client- receive its configuration information from aDHCP server

Communicates with DHCP server to obtain IP addresses

and TCP/IP configuration information as defined by the

administrator

DHCP Leases

Defines the duration for which a DHCP server loans an

IP to a DHCP client (1 minute to 999 days, or unlimited)

Default lease duration is 8 days

TermsTerms


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DHCPDI

SC

OVE

R- sent by clients via broadcast to locatea DHCP server

DHCPOFFER- Sent by DHCP servers to a DHCP client in

response to DHCPDIS

COV

ER

along with offeredparameters

DHCPREQUEST- Sent by DHCP client as a broadcast

message to signal its acceptance or rejection of offeredaddress and parameters

Examples of DHCP LeasesExamples of DHCP Leases


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DHCPDECLINE- Sent by the DHCP client to a DHCPserver to decline an offered IP if the IP is already in use.Lease process must be restarted.

DHCPACK- Sent by a DHCP server to a DHCP client toconfirm an IP address and provide the client with

configuration requested parameters.


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DHCPNACK- Sent by a DHCP server to a DHCP client todeny the clients

DHCPREQUEST.

Occurs if requested address is incorrect because theclient was moved to a new subnet, or because theclients lease expired and cannot be renewed.

Lease process must be restarted

Examples of DHCP LeasesExamples of DHCP Leases


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DHCPRELEASE- Sent by a DHCP client to a DHCPserver that provided the lease to relinquish an IP andcancel the remaining lease.

DHCPINFORM- Sent from a DHCP client to a DHCPserver to ask for additional local configuration parameters;the client already has a configured IP.

Also used to detect unauthorized DHCP servers


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Lease process is performed in the following situations: First time the client boots

After releasing its IP address

After receiving a DHCPNACK message, in response

to a DHCP client attempting to renew a previously

leased address

Initial Lease ProcessInitial Lease Process


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Prior to Windows 2000, any user could create a DHCPserver on the network, this led to conflicts in IPassignments.

In Windows 2000/ 2003 an unauthorized DHCP server(rogue) is not listed in the Active Directory and is notauthorized. This is a benefit of Active Directory

Authorizing a DHCP ServerAuthorizing a DHCP Server


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At initialization the DHCP server contacts Active Directoryto determine whether the server is on the authorized list.

If server is authorized, DHCP service starts

If server is not on the list, the DHCP Server service

logs an error in the event log, does not start, and will

not respond to client requests

Authorization ProcessAuthorization Process


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When a DHCP server that is not a member of a domain(work group) initializes the following happens:

The server broadcasts a DHCPINFORM message onthe network

Other servers receiving this message respond with aDHCPACK message and provides the name of thedirectory domain it is part of

Protecting Against ImproperUse of Workgroup DHCP ServersProtecting Against ImproperUse of Workgroup DHCP Servers


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If a workgroup DHCP server detects another memberDHCP server of a domain on the network, theworkgroup DHCP server assumes itself to beunauthorized on that network and shuts itself down

If the workgroup DHCP server detects the presenceof another workgroup server, it ignores it, this meansmultiple workgroup servers can be active at the sametime as long as there is no directory service


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Scope determines which IP addresses are allocated toclients. You can configure as many scopes as needed foryour network environment

Scope must be defined and activated before DHCP clients

can use the DHCP server for dynamic TCP/IP configuration

An administrator can configure one or more scopes on oneor more 2003 servers, but scope information is notcommunicated from server to server

Be careful not to have servers assigning the sameIPs to multiple clients, or assigning IPs that arestatically assigned to IP hosts

DHCP ScopeDHCP Scope


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MS-DHCP Server allows Multicast addressing

Assigned in the same fashion as unicast addressing

Completely utilizes existing infrustructure

Used with conferencing or audio applications, which

require users to specifically configure multicast

addresses.

Multicast and Unicast AddressingMulticast and Unicast Addressing


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Not the same as IP broadcast, which must bereadable by all network computers, while multicast

addressing points to a specific group of computers,

using the concept of group membership to identify

those who are to receive the message


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Used for DHCP-enabled hosts that need to have staticIP addresses on your network, such as: Email servers,

Application servers, File and Print servers

Enable permanent address lease assignment

Must be created within a scope

Excluded addresses are not available for clientreservation

DHCP ReservationsDHCP Reservations


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The reserved IP should be set aside for the device thathas the MAC (physical) address associated with thatreserved IP.

Therefore you must know the MAC address for eachdevice needing to be reserved

MAC address can be determined by typing: ipconfig /allat the command line


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A superscope is an administrative grouping of scopes usedto support multinets, or multiple logical subnets (sub-divisions of an IP network)

Multinetting commonly occurs when the number of hosts

grows beyond the capacity of the original address space

Separate scopes are grouped into superscopesincreasing address capacity

Using SuperscopesUsing Superscopes


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Used to specify additional IP settings

Router (gateway), DNS servers, WINS servers, etc.

Option Types:

To a single reserved clientReservation options

A specific vendor classClass options

Clients from specific scopeScope options

All scopes on the serverServer options

Applies to:Option Type

DHCP Scope Options


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MCSE 05 Implementing of a Network Infrastructure 03 Theory