DHCPDHCP Dynamic Host Configuration Dynamic Host Configuration

ProtocolProtocol

By By

Curtis Wright IIICurtis Wright III

DHCP Definition DHCP Definition

Dynamic Host Configuration Protocol(DHCP) Dynamic Host Configuration Protocol(DHCP) provides a framework for passing provides a framework for passing configuration information to hosts on a configuration information to hosts on a TCP/IP network. DHCP is based on the TCP/IP network. DHCP is based on the Bootstrap Protocol(BOOTP) adding the Bootstrap Protocol(BOOTP) adding the capability of automatic allocation of capability of automatic allocation of reusable network addresses and additional reusable network addresses and additional configuration options. DHCP captures the configuration options. DHCP captures the behavior of BOOTP relay agents. DHCP behavior of BOOTP relay agents. DHCP participants can interoperate with BOOTP participants can interoperate with BOOTP participants.participants.

DHCP OriginsDHCP Origins

DHCP is the result of the Dynamic Host DHCP is the result of the Dynamic Host Configuration (DHC) working group of Configuration (DHC) working group of the IETF addressing the issue they the IETF addressing the issue they defined on their first meeting in April defined on their first meeting in April 1989 in Cocoa Beach, FL of the 1989 in Cocoa Beach, FL of the automated allocation of a network automated allocation of a network address and transmission of other address and transmission of other parameters such as the subnet mast parameters such as the subnet mast and a default router.and a default router.

DHCP RFC Sequence DHCP RFC Sequence

RFC 1531 which was published in RFC 1531 which was published in October of 1993 followed by 1541 October of 1993 followed by 1541 same and month followed by RFC same and month followed by RFC 2131 in 1997. 2131 in 1997.

Ralph Droms was the original author of Ralph Droms was the original author of DHCP and it currently involved on its DHCP and it currently involved on its ongoing evolution.ongoing evolution.

Predecessors to DHCP Predecessors to DHCP

1.1. Reverse Address Resolution Reverse Address Resolution Protocol (RARP)Protocol (RARP)

2.2. Bootstrap Protocol (BOOTP) Bootstrap Protocol (BOOTP)

RARPRARP Provides a mechanism for a host to determine Provides a mechanism for a host to determine

its IP address when it is only aware of its MAC its IP address when it is only aware of its MAC address.address.

RARP can determine and configure a diskless RARP can determine and configure a diskless workstation with an IP address.workstation with an IP address.

No method for determining and delivering No method for determining and delivering other configuration data.other configuration data.

RARP server can service only a single subnet RARP server can service only a single subnet because of its complete reliance on Ethernet because of its complete reliance on Ethernet broadcasts.broadcasts.

RFC 903RFC 903

BOOTP BOOTP

Developed as answer to RARP’s Developed as answer to RARP’s limitations.limitations.

BOOTP allows hosts to be dynamically BOOTP allows hosts to be dynamically configured to use the TCP/IP protocol suite.configured to use the TCP/IP protocol suite.

BOOTP delivers configuration information BOOTP delivers configuration information automatically instead of each TCP/IP host automatically instead of each TCP/IP host on a network being manually configured.on a network being manually configured.

RFC 951RFC 951

BOOTP BOOTP BOOTP is a client/server process where the BOOTP BOOTP is a client/server process where the BOOTP

client, during the boot phase, requests configuration client, during the boot phase, requests configuration information from a BOOTP server.information from a BOOTP server.

After receiving a request from a BOOTP client, the After receiving a request from a BOOTP client, the server looks up the clients MAC address in its BOOTP server looks up the clients MAC address in its BOOTP configuration database and sends a reply containing IP configuration database and sends a reply containing IP configuration information.configuration information.

Client receives the reply and configures its TCP/IP stack.Client receives the reply and configures its TCP/IP stack. BOOTP client will also load a boot file if the BOOTP BOOTP client will also load a boot file if the BOOTP

server supplies a path using the fully qualified filename.server supplies a path using the fully qualified filename. The magic cookie, a mechanism for a BOOTP server to The magic cookie, a mechanism for a BOOTP server to

supply vendor-specific operating system(OS) options to supply vendor-specific operating system(OS) options to a BOOTP client. Options include DNS servers, WINS or a BOOTP client. Options include DNS servers, WINS or NetBIOS name server, time servers, etc.NetBIOS name server, time servers, etc.

BOOTP BOOTP Even with these improvements BOOTP Even with these improvements BOOTP

had serious drawbacks such as:had serious drawbacks such as:

1. BOOTP database was a static text 1. BOOTP database was a static text file.file.

File had to be maintained by hand as File had to be maintained by hand as changes were made to the network.changes were made to the network.

2. Unable to dynamically allocate and 2. Unable to dynamically allocate and distribute IP addresses.distribute IP addresses.

Dynamic IP addressing was critical when Dynamic IP addressing was critical when IP address space was limited.IP address space was limited.

BOOTP ConversationBOOTP Conversation

Two types of BOOTP messages:Two types of BOOTP messages:

1. BOOTREQUEST1. BOOTREQUEST

2. BOOTREPLY2. BOOTREPLY

BOOTREQUEST/BOOTREPLYBOOTREQUEST/BOOTREPLY

Have the sane packet structure.Have the sane packet structure. BOOTREQUEST includes information BOOTREQUEST includes information

that allows the BOOTP server to that allows the BOOTP server to determine what configuration data it determine what configuration data it must supply the requesting host.must supply the requesting host.

BOOTREPLY includes the information BOOTREPLY includes the information that the client requested of the that the client requested of the server.server.

BOOTREQUEST BOOTREQUEST

Contains following information:Contains following information:

1. Source’s MAC address 1. Source’s MAC address

2.Destination’s MAC address2.Destination’s MAC address

3. Destination’s IP address3. Destination’s IP address

4.Source’s IP address4.Source’s IP address

5. Destination server hostname5. Destination server hostname

6. Boot filename6. Boot filename

7. Vendor-specific data7. Vendor-specific data

BOOTP/DHCP similaritiesBOOTP/DHCP similarities DHCP has many of the same DHCP has many of the same

characteristics as BOOTP such ascharacteristics as BOOTP such as

1.Client/server operating model1.Client/server operating model

2.Packet structure2.Packet structure

3.UDP port numbers3.UDP port numbers

a. messages from a client to a a. messages from a client to a server are sent to the ‘server’ port server are sent to the ‘server’ port (67).(67).

b. Messages from a server to a b. Messages from a server to a client are sent to the ‘client’ port client are sent to the ‘client’ port (68).(68).

BOOTP/DHCP DifferencesBOOTP/DHCP Differences

There are two primary differences There are two primary differences between DHCP and BOOTP:between DHCP and BOOTP:

1.1. DHCP defines a mechanism through DHCP defines a mechanism through which clients can be assigned a which clients can be assigned a network address for a finite lease, network address for a finite lease, allowing for serial reassignment of allowing for serial reassignment of network addresses to different network addresses to different clients.clients.

2.2. DHCP provides the mechanism for a DHCP provides the mechanism for a client to acquire all of the IP client to acquire all of the IP configuration parameters that it configuration parameters that it needs in order to operate.needs in order to operate.

DHCP Message formatDHCP Message format

DHCP Message Field DesciptionsDHCP Message Field Desciptions

FieldsFields OcOctettetss

DescriptionsDescriptions

opop 11

op code/message typeop code/message type

htypehtype 11

Hardware address typeHardware address type

hlenhlen 11

hardware address lengthhardware address length

hopshops 11

Client sets to zero, optionally used by relay agents when booting via relay agentClient sets to zero, optionally used by relay agents when booting via relay agent

xidxid 44

Transaction IDTransaction ID

secssecs 22

Filled in by client, seconds elapsed since client began address acquisition or renewal Filled in by client, seconds elapsed since client began address acquisition or renewal process.process.

flagsflags 22

flagsflags

ciaddciaddrr

44

Client IP addressClient IP address

yiaddyiaddrr

44

‘‘your’ (client) IP addressyour’ (client) IP address

siaddsiaddrr

44

IP address of next server to use in bootstrap; returned in DHCPOFFER, DHCPACK by IP address of next server to use in bootstrap; returned in DHCPOFFER, DHCPACK by server.server.

giaddgiaddrr

44

Relay agent IP addressRelay agent IP address

chaddchaddrr

1616

Client hardware addressClient hardware address

snamsnamee

6464 Optional server host name, null terminated stringOptional server host name, null terminated string..

filefile 121288

Boot file nameBoot file name

optiooptionsns

varvar

Optional parameters field.Optional parameters field.

DHCP Allocation DHCP Allocation MechanismsMechanisms

DHCP supports three mechanisms for IP allocation:DHCP supports three mechanisms for IP allocation: 1.Automatic – a permanent IP address is assigned 1.Automatic – a permanent IP address is assigned

to a client.to a client. 2.Dynamic – an IP address is assigned for a 2.Dynamic – an IP address is assigned for a

limited amount of time.limited amount of time. 3.Manual – a client’s IP address is assigned by 3.Manual – a client’s IP address is assigned by

network administrator, and DHCP conveys that network administrator, and DHCP conveys that address to the client.address to the client.

A network could use one or more of these A network could use one or more of these mechanisms depending on the network mechanisms depending on the network administrator’s policies.administrator’s policies.

Dynamic AllocationDynamic Allocation

1. Allows automatic reuse of an address that 1. Allows automatic reuse of an address that is no longer needed by the client to which it is no longer needed by the client to which it is assigned.is assigned.

2. Useful for assigning an address to a client 2. Useful for assigning an address to a client that will be connected to the network that will be connected to the network temporarily or for sharing a limited pool of temporarily or for sharing a limited pool of IP addresses among a group of clients that IP addresses among a group of clients that do not need permanent IP addresses.do not need permanent IP addresses.

3. Good for assigning an IP address to a new 3. Good for assigning an IP address to a new client being permanently connected to a client being permanently connected to a network having a limited number of IP network having a limited number of IP addresses that it is necessary to reclaim addresses that it is necessary to reclaim them when old clients are retired.them when old clients are retired.

DHCP server and client DHCP server and client messagesmessages

From client From client From serverFrom server

DHCPDISCOVERDHCPDISCOVER DHCPOFFERDHCPOFFER

DHCPREQUESTDHCPREQUEST DHCPACKDHCPACK

DHCPDECLINEDHCPDECLINE DHCPNACKDHCPNACK

DHCPRELEASEDHCPRELEASE

DHCPINFORMDHCPINFORM

DHCP messagesDHCP messages DHCPDISCOVER- Client broadcast to DHCPDISCOVER- Client broadcast to

locate available servers.locate available servers. DHCPOFFER- Server to client in DHCPOFFER- Server to client in

response to DHCPDISCOVER with offer response to DHCPDISCOVER with offer of configuration parameters. of configuration parameters.

DHCPREQUEST – Client message to DHCPREQUEST – Client message to servers either (a) requesting offered servers either (a) requesting offered parameters from one server and parameters from one server and implicitly declining offers from all implicitly declining offers from all others, (b) confirming correctness of others, (b) confirming correctness of previously allocated address after, e.g., previously allocated address after, e.g., system reboot, or (c) extending the system reboot, or (c) extending the lease on a particular network addresslease on a particular network address

DHCPACK Server to client with DHCPACK Server to client with configuration parameters, including configuration parameters, including committed network address.committed network address.

DHCP messages (contd)DHCP messages (contd) DHCPNACK – Server to client indicating DHCPNACK – Server to client indicating

client notion of network address is client notion of network address is incorrect or client’s lease as expired.incorrect or client’s lease as expired.

DHCPDECLINE – Client to server DHCPDECLINE – Client to server indicating network address is already indicating network address is already in use.in use.

DHCPRELEASE – Client to server DHCPRELEASE – Client to server relinquishing network address and relinquishing network address and cancelling remaining leasecancelling remaining lease

DHCPINFORM – Client to server, asking DHCPINFORM – Client to server, asking only for local configuration only for local configuration parameters; client already has parameters; client already has externally configured network address.externally configured network address.

DHCP client and server messages when allocating a DHCP client and server messages when allocating a new network addressnew network address

Server(Not Selected)

Client Server(selected)

Begins initialization

DHCPDISCOVER

Determines configuration

DHCPOFFER

Collects RepliesSelects configuration

DHCPREQUEST

DHCPDISCOVER

Determines Configuration

DHCPREQUESTCommits configuration

DHCPACK

Initialization complete

Graceful shutdown

DHCPRELEASEDiscards lease

DHCP client and server messages for previously DHCP client and server messages for previously allocated network addressallocated network addressServer Client Server

Begins Initialization

Locates Configuration

Locates Configuration

DHCPACKDHCPACK

Initialization completeSubsequent DHCPACKs ignored

Constructing and sending Constructing and sending DHCP messagesDHCP messages

DHCP clients and servers both construct DHCP DHCP clients and servers both construct DHCP messages by filling in fields in the fixed messages by filling in fields in the fixed format section of the message and appending format section of the message and appending tagged data items in the variable length tagged data items in the variable length option area.option area.

Options area includes first a four-octet ‘magic Options area includes first a four-octet ‘magic cookie’, followed by the options which comes cookie’, followed by the options which comes from BOOTP.from BOOTP.

The last option must ALWAYS be the ‘end’ The last option must ALWAYS be the ‘end’ option.option.

Constructing and sending Constructing and sending DHCP messages (contd)DHCP messages (contd)

DHCP messages broadcast by a client prior to DHCP messages broadcast by a client prior to that client obtaining its IP address must have the that client obtaining its IP address must have the source address field in the IP header set to 0.source address field in the IP header set to 0.

DHCP clients are responsible for all message DHCP clients are responsible for all message retransmission. The client MUST adopt a retransmission. The client MUST adopt a retransmission strategy that incorporates a retransmission strategy that incorporates a randomized exponential backoff algorithm to randomized exponential backoff algorithm to determine the delay between retransmissions.determine the delay between retransmissions.

DHCP servers and BOOTP relay agents attempt to DHCP servers and BOOTP relay agents attempt to deliver DHCPOFFER, DHCPACK, and DHCPNACK deliver DHCPOFFER, DHCPACK, and DHCPNACK messages directly to the client using unicast messages directly to the client using unicast delivery.delivery.

DHCP server administrative DHCP server administrative controlscontrols

A DHCP server has a block of network A DHCP server has a block of network addresses from with it can satisfy addresses from with it can satisfy requests for new addresses.requests for new addresses.

Each server maintains a database of Each server maintains a database of allocated addresses and leases in local allocated addresses and leases in local permanent storage.permanent storage.

DHCP server are not required to respond DHCP server are not required to respond to every DHCPDISCOVER and to every DHCPDISCOVER and DHCPREQUEST message they receive.DHCPREQUEST message they receive.

DHCP server needs to use some unique DHCP server needs to use some unique identifier to associate a client with its identifier to associate a client with its lease.lease.

DHCP clients are free to use any strategy DHCP clients are free to use any strategy in selecting a DHCP server among those in selecting a DHCP server among those from which the client receives a from which the client receives a DHCPOFFER message.DHCPOFFER message.

DHCP Server Behavior DHCP Server Behavior While not required for correct operation of DHCP, the sever While not required for correct operation of DHCP, the sever

SHOULD NOT use the selected network address before the SHOULD NOT use the selected network address before the client responds to the server’s DHCPOFFER message.client responds to the server’s DHCPOFFER message.

Procedure for server choosing an expiration time for a lease:Procedure for server choosing an expiration time for a lease:

If the client has not requested a specific lease in the If the client has not requested a specific lease in the DHCPDISCOVER message and the client already has an DHCPDISCOVER message and the client already has an assigned network address, the server returns the lease assigned network address, the server returns the lease expiration time previously assigned to that address(note expiration time previously assigned to that address(note that the client must explicitly request a specific lease to that the client must explicitly request a specific lease to extend the expiration time on a previously assigned extend the expiration time on a previously assigned address),address),

ELSEIF ELSEIF the client has not requested a specific lease in the the client has not requested a specific lease in the

DHCPDISCOVER message and the client does not have an DHCPDISCOVER message and the client does not have an assigned network address, the server assigns a locally assigned network address, the server assigns a locally configured default lease time, ELSE configured default lease time, ELSE

If the client has requested a specific lease in the If the client has requested a specific lease in the DHCPDISCOVER message(regardless of whether the client DHCPDISCOVER message(regardless of whether the client has an assigned network address) , the server may choose has an assigned network address) , the server may choose either to return the requested lease( if the lease is either to return the requested lease( if the lease is acceptable to local policy) or select another lease.acceptable to local policy) or select another lease.

DHCP server behavior DHCP server behavior (contd)(contd)The sever must return to the client:The sever must return to the client:

1.1. The client’s network addressThe client’s network address2.2. The expiration time for the client’s leaseThe expiration time for the client’s lease3.3. Parameters requested by the client based on Parameters requested by the client based on

specified rules. 4. The server MUST supply as specified rules. 4. The server MUST supply as many of the requested parameters as possible many of the requested parameters as possible and MUST omit any parameters it cannot provide.and MUST omit any parameters it cannot provide.

5.Any parameters from the existing binding that 5.Any parameters from the existing binding that differ from the Host Requirements Document differ from the Host Requirements Document defaults, defaults,

6.Any parameters specific to this client6.Any parameters specific to this client7.Any parameter specific to this client’s class; the 7.Any parameter specific to this client’s class; the

parameters must be identified by an exact match parameters must be identified by an exact match between the client’s vendor class identifiers and between the client’s vendor class identifiers and the client’s classes identified in the serverthe client’s classes identified in the server

8.Parameters with non-default values on the client’s 8.Parameters with non-default values on the client’s subnet.subnet.

State transition diagram for clientState transition diagram for client

INIT-REBOOT INIT

REBOOTING

REBINDING

REQUESTING

RENEWINGBOUND

SELECTING

DHCPACK/Record lease, set timers T1, T2

T1 expires Send DHCPREQUEST toLeasing server

Send

DHCPREQUEST

DHCPACK/Record lease,set timers T1, T2

DHCPAK/Halt Network

DHCPOFFER,DHCPACK,DHCPNAKDiscard

DH

CP

AC

K/R

ecord lease, set

Tim

ers T1, T

2

DHCPOFFER/Discard

DHCPNAK/

Restart

DHCPNAK/

Discard offer

DHCPACK/Record lease, set

timers T1, T2

DHCPOFFER/Collect Replies

DHCPACK(not accept)/S

end DHCPDECLINE

Select offer/send

DHCPREQUEST

Send

DHCPDISCOVER

DH

CP

AC

K/R

ecor

d le

ase,

Set

tim

ers

T1, T

2

Some DHCP drawbacksSome DHCP drawbacks A malicious user could make trouble by A malicious user could make trouble by

putting up an unofficial DHCP server. putting up an unofficial DHCP server. The "broadcast flag": DHCP includes a way The "broadcast flag": DHCP includes a way

in which client implementations unable to in which client implementations unable to receive a packet with a specific IP address receive a packet with a specific IP address can ask the server or relay agent to use the can ask the server or relay agent to use the broadcast IP address in the replies (a "flag" broadcast IP address in the replies (a "flag" set by the client in the requests set by the client in the requests

An easy mistake to make in setting up a An easy mistake to make in setting up a DHCP server is to fail to set all the DHCP server is to fail to set all the necessary global parameters. necessary global parameters.

Long leases can be disadvantageous in Long leases can be disadvantageous in cases where you need to change a cases where you need to change a configuration parameter or withdraw an configuration parameter or withdraw an address from use. address from use.

DHCP securityDHCP security

DHCP which is built on UDP and IP DHCP which is built on UDP and IP and is used to make maintenance of and is used to make maintenance of remote and/or diskless hosts easier remote and/or diskless hosts easier in its current form is quite insecure.in its current form is quite insecure.

IPv6(IPng) or IP Next GenerationIPv6(IPng) or IP Next Generation

It has been foreseen due to the rapid growth It has been foreseen due to the rapid growth of the Internet and its initial design that there of the Internet and its initial design that there will come a point where there will not be any will come a point where there will not be any available addresses to connect new hosts.available addresses to connect new hosts.

IPv6 is one of several solutions that has been IPv6 is one of several solutions that has been proposed to deal with this issue.proposed to deal with this issue.

IPv6 has a stateless autoconfiguration IPv6 has a stateless autoconfiguration capability.capability.

Stateless autoconfiguration does not require Stateless autoconfiguration does not require manual host configuration, minimal router manual host configuration, minimal router configuration, and no additional servers. A configuration, and no additional servers. A host is able generate its own addresses using host is able generate its own addresses using a combination of locally available information a combination of locally available information and information advertised by routers.and information advertised by routers.

Future of DHCPFuture of DHCP1. DHCP for IPv6 is the future for DHCP .1. DHCP for IPv6 is the future for DHCP .2. DHCPv6 complements IPv6 by providing a 2. DHCPv6 complements IPv6 by providing a stateful autoconfiguration option to facilitate stateful autoconfiguration option to facilitate

the automatic configuration of DHCP the automatic configuration of DHCP clients(RFC 3315).clients(RFC 3315).

In stateful autoconfiguration, hosts obtain In stateful autoconfiguration, hosts obtain interface addresses and/or configuration interface addresses and/or configuration information and parameters from a server. information and parameters from a server. The server maintains a database of the The server maintains a database of the addresses that have been to which hosts.addresses that have been to which hosts.

3.DHCP clients can get configuration options 3.DHCP clients can get configuration options such as DNS server addresses.such as DNS server addresses.

4. DHCPv6 uses a combination of unicast and 4. DHCPv6 uses a combination of unicast and multicast messages instead of broadcast multicast messages instead of broadcast message for the majority of its message for the majority of its conversation.conversation.

ReferencesReferences

1.www.dhcp.org1.www.dhcp.org

2.DHCP for Windows 20002.DHCP for Windows 2000

3.The DHCP handbook3.The DHCP handbook

Exam QuestionsExam Questions

1.1. Provide timeline diagram of Provide timeline diagram of messages exchanged between messages exchanged between DHCP client and servers when DHCP client and servers when allocating a new network address.allocating a new network address.

2.2. List the predecessors to DHCP with List the predecessors to DHCP with their advantages and their advantages and disadvantages and explain why disadvantages and explain why DCHP is better.DCHP is better.

Exam Question AnswersExam Question Answers Server Server Client Server Client Server

(not selected) (selected)(not selected) (selected) V V VV V V | | || | | | Begins Initialization || Begins Initialization | | | || | | | -------------------------------/ | \ ---------------------------------------- || -------------------------------/ | \ ---------------------------------------- | | / DHCPDISCOVER | DHCPDISCOVER \ || / DHCPDISCOVER | DHCPDISCOVER \ | | | || | | Determines Configuration | Determines Configuration Determines Configuration | Determines Configuration | | || | | | \----------------------- | ----------------------------------/ || \----------------------- | ----------------------------------/ | | DHCPOFFER \ | / DHCPOFFER || DHCPOFFER \ | / DHCPOFFER | | \ | / || \ | / | | Collects Replies || Collects Replies | | \ | || \ | | | Selects Configuration || Selects Configuration | | | || | | | ___________________/ | \__________________________ || ___________________/ | \__________________________ | | / DHCPREQUEST | DHCPREQUEST \ || / DHCPREQUEST | DHCPREQUEST \ | | | || | | | | Commits configuration| | Commits configuration | | || | | | | _________________________/ || | _________________________/ | | | / DHCPACK || | / DHCPACK | | | || | | | Initialization complete || Initialization complete |

Exam Question Answers(Contd)Exam Question Answers(Contd)

Predecessors to DHCP are Predecessors to DHCP are

1.RARP(Reverse Address Resolution Protocol)1.RARP(Reverse Address Resolution Protocol)

BenefitsBenefits

a. Provides a mechanism for a host to a. Provides a mechanism for a host to determine its IP address when it is only aware of determine its IP address when it is only aware of its MAC addressits MAC address

b. RARP can determine and configure a b. RARP can determine and configure a diskless workstation with an IP address.diskless workstation with an IP address.

DisadvantagesDisadvantages

a. No method for determining and delivering a. No method for determining and delivering other configuration data.other configuration data.

b. RARP server can service only a single b. RARP server can service only a single subnet because of its complete reliance on subnet because of its complete reliance on Ethernet broadcastsEthernet broadcasts

Exam Question Answers(Contd)Exam Question Answers(Contd)2.2. BOOTP(Bootstrap Protocol)BOOTP(Bootstrap Protocol) Benefits Benefits a. BOOTP allows hosts to be dynamically a. BOOTP allows hosts to be dynamically

configured to use the TCP/IP protocol suiteconfigured to use the TCP/IP protocol suite b. BOOTP delivers configuration b. BOOTP delivers configuration

information automatically instead of each information automatically instead of each TCP/IP host on a network being manually TCP/IP host on a network being manually configuredconfigured

DisadvantagesDisadvantages a. BOOTP database was a static text file a. BOOTP database was a static text file

which was maintained by hand as network which was maintained by hand as network changes were made.changes were made.

b. Unable to dynamically allocate and b. Unable to dynamically allocate and distribute IP addresses.distribute IP addresses.

Exam Question Answers(Contd)Exam Question Answers(Contd)

DHCP is better because DHCP is better because

a. DHCP defines a mechanism through which a. DHCP defines a mechanism through which clients can be assigned a network address clients can be assigned a network address for a finite lease, allowing for serial for a finite lease, allowing for serial reassignment of network addresses to reassignment of network addresses to different clients.different clients.

b. DHCP provides the mechanism for a client b. DHCP provides the mechanism for a client to acquire all of the IP configuration to acquire all of the IP configuration parameters that it needs in order to parameters that it needs in order to operate.operate.