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
WRKWRK--LONLON--001001
WRKWRK--LONLON--003003
WRKWRK--LONLON--003003
needs an IPneeds an IP
addressaddress
X
LeasingLeasing
192.168.29.1 to192.168.29.1 to
WRKWRK--LONLON--003003
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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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