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Server 2012 MOAC 70-410 > Lesson 11: Deploying and Configuring the DHCP Service > Flashcards

Lesson 11: Deploying and Configuring the DHCP Service Flashcards

1
Q

3 components of DHCP

A

Server application - responds to client requests for TCP/IP config settings
Client – Issues requests and applies received TCP/IP config settings
Communications protocol - Defines formats and sequences of the messages exchanged by DHCP clients and servers

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2
Q

IETF

A

Internet Engineering Task Force

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3
Q

Which IETF RFC describes DHCP

A

RFC 2131

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4
Q

Which IETF RFC describes DHCP options and bootp vendor extensions?

A

RFC 2132

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5
Q

3 types of DHCP allocation methods

A

Dynamic allocation
Automatic allocation
Manual allocation

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6
Q

DHCP dynamic allocation method

A

Server assigns client IP lease from a scope of IPs for a period of time. Client must renew lease. If not renewed, IP goes back into the scope for reassignment

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7
Q

DHCP automatic allocation method

A

Dynamic allocation with an indefinite lease. Reduces network traffic by eliminating lease renewals but does not allow for much change without reconfiguring the PC manually

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8
Q

DHCP manual allocation method

A

Server assigns IP permanently to client. Called a reservation.

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9
Q

BOOTP

A

Bootstrap Protocol. Allows a diskless client to boot from a network resource

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10
Q

DHCP packet

Size & description: op field

A

AKA Op code
1 byte
Specifies whether the message is a request or a reply

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11
Q

DHCP packet

Size & description: htype

A

AKA hardware type
1 bytes
Specifies the type of hardware address used in the chaddr field

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12
Q

DHCP packet

Size & description: hlen

A

AKA hardware address length
1 byte
Specifies the length of the hardware address in the chaddr field, in bytes

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13
Q

DHCP packet

Size & description: hops

A

1 byte

Specifies the number of network segments between client /server. CLient sets to 0. Each DHCP relay increments by 1

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14
Q

DHCP packet

Size & description: xid

A

Transaction ID
4 bytes
Contains transaction ID used to associate the request and response messages of a single DHCP transaction

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15
Q

DHCP packet

Size & description: secs

A

Seconds
2 bytes
Specifies the number of secs elaps since ip was assigned or lease last renewed

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16
Q

DHCP packet

Size & description: flags

A

2 bytes
Contains broadcast flag as first bit. When set to 1, specifies DHCP servers and relay agents should use broadcasts, not unicasts

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17
Q

DHCP packet

Size & description: ciaddr

A

Client IP address
4 bytes
Specifies the clients IP address in DHCPREQUEST messages transmitted while in the bound, renewal, or rebinding state

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18
Q

DHCP packet

Size & description: yiaddr

A

Your IP address
4 bytes
Specifies the IP address being offered or assigned by the server in DHCPOFFER or DHCPACK messages

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19
Q

DHCP packet

Size & description: siaddr

A

Server IP address
4 bytes
Specifies IP addr of the next server in bootstrap sequence. Only included when DHCP is configured to supply executable boot file to clients & files located on a different server

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20
Q

DHCP packet

Size & description: giaddr

A

Gateway IP Address
4 bytes
Specifies the ip addr of the DHCP replay agent the server should send its replies when a client and server are located at different subnets

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21
Q

DHCP packet

Size & description: chaddr

A

Client Hardware Address
16 bytes
Specifies the hardware address of the client system in CHCPDISCOVER and DCHPREQUEST messages, which the server uses to address its unicast responses to the client

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22
Q

DHCP packet

Size & description: sname

A

Server Host Name
64 bytes
Specifies the optional host name of the DHCP server. More commonly used to hold overflow data from the options field

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23
Q

DHCP packet

Size & description: file

A

Boot file name
128 bytes
Specifies the name of an executable boot file for diskless client workstation. More commonly used to hold overflow data from the option field

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24
Q

DHCP packet

Size & description: options

A

Variable size. Min of 312 bytes
Contains magic cookie that specifies how the rest of the field should be interpreted and the DHCP Message Type option that defines the function of the message.

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25
Q

8 different message types

A 
DHCPDISCOVER
DHCPOFFER
DHCPREQUEST
DHCPDECLINE
DHCPACK
DHCPNAK
DHCPRELEASE
DHCPINFORM
26
Q

The options field of a DHCP packet always begins with _____

A

The magic cookie

27
Q

Magic cookie

A

Portion of the DHCP options field that informs the server about what is contained in the rest of the field. 4 byte subfield.

28
Q

DHCPDISCOVER

A

Used by clients requesting config params from a DHCP server

29
Q

DHCPOFFER

A

Used by server to offer IP addresses to requesting clients

30
Q

DHCPREQUEST

A

Used by clients to accept or renew an ip address assignment

31
Q

DHCPDECLINE

A

Used by clients to reject an offered IP address

32
Q

DHCPACK

A

Used by server to acknowledge a client’s acceptance of an offered IP address

33
Q

DHCPNAK

A

Used by servers to reject a client’s acceptance of an offered IP address

34
Q

DHCPRELEASE

A

Used by clients to terminate an IP address lease

35
Q

DHCPINFORM

A

Used by clients to obtain additional TCP/IP config params

36
Q

Which transport layer protocol is used to carry DHCP packets?

A

UDP

37
Q

What BOOTP vendor info extensions are included in the DHCP option field and used by most clients?

A 
Subnet mask
Router / default route
domain name server
host name
domain name
38
Q

What DHCP message does a client send first when seeking an IP address?

A

DHCPDISCOVER

39
Q

When a DHCP server received DHCPDISCOVER and has an ip available, what does it send?

A

DHCPOFFER

40
Q

If a client received a DHCPOFFER and wants the address, what does it send?

A

DHCPREQUEST

41
Q

If a client sends a server a DHCPREQUEST but the offered IP is no longer available, what does the server send back?

A

DHCPNAK

42
Q

If a client sends a server a DHCPREQUEST and the offered IP is still available, what does the server send back?

A

DHCPACK

43
Q

init state

A

A client with no ip, looking for the DHCP server (having sent DHCPDISCOVER messages)

44
Q

Why might A client may receive DHCPOFFERs from more than on DHCP server?

A

Client sent a DHCPDISCOVER message as a broadcast. If there’s more than one DHCP server, both may respond.

45
Q

If a client receives DHCPACK for an IP, what does it then do?

A

Attempts an ARP test to confirm that the offered IP really isn’t in use in its network segment.

46
Q

If an offered IP fails an ARP test, what does the client send to the DHCP server?

A

DHCPDECLINE

47
Q

If an offered IP passes the ARP test, what happens?

A

Client is “bound”. Transaction complete.

48
Q

What is the default ip lease time for a DHCP client in server 2012?

A

8 days

49
Q

When is renewal time on a DHCP lease?

A

At 50% of the way through the lease time.

50
Q

Renewal time AKA

A

T1

51
Q

What state does a client enter at renewal time?

A

Renewing State

52
Q

Besides at renewal time, when do DHCP clients renew their lease?

A

On reboot

53
Q

What happens if the DHCP server does not respond to a client’s request to renew a lease via its DHCPREQUEST mesasgess?

A

Client enters rebinding state and beings transmitting DHCPREQUEST messages as broadcasts, attempting an IP assignment from any DHCP server on the network

54
Q

At what point does a client enter rebinding state?

A

87.5% into lease duration (T2) after DHCP server failed to respond to T1 renewal requests.

55
Q

Distributed DHCP infrastructure

A

Locating a DHCP server on each of your subnets – one per broadcast domain

56
Q

Advantages of distributed DHCP infrastructure

A

Clients have easy access to their DHCP servers
Do not have to worry about DHCP traffic adding to the burden of your routers. All client/server traffic for DHCP will be local

57
Q

Centralized DHCP infrastructure

A

DHCP servers are all placed in a single location. Request pass through subnets. Relay agents are required on each individual broadcast domain

58
Q

DHCP relay agent

A

Receives DHCP broadcast traffic on a subnet / broadcast domain and sends it to a DHCP server on at least one other subnet. DHCP servers send messages back to the agent, which processes and sends them to the client.

59
Q

What devices often have DHCP relay agents built in?

A

Routers

60
Q

On what and how does centralizing a DHCP server create a burden?

A

Creates a burden on the DHCP server and on the subnet the central server is located, b/c of increased traffic

61
Q

PXE

A

PreBoot Execution Environment

Allows a DHCP server to specify a boot file for a client to download and boot from.

62
Q

What does PXE use to transfer the boot files specified by the DHCP server?

A

TFTP - Trivial File Transfer Protocol

Server 2012 MOAC 70-410 (18 decks)

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