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Networking II > Ch10 DHCP - Theory > Flashcards

Ch10 DHCP - Theory Flashcards

1
Q

DHCP Definition

A

Dynamic Host Configuration Protocol

Protocol that dynamically assigns IP addresses and other network configuration information.

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2
Q

DHCP Address Allocation Mechanisms

A
  1. Manual Allocation
  2. Automatic Allocation
  3. Dynamic Allocation
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3
Q

DHCP Manual Allocation

A

Admin. assigns a pre-allocated IPv4 address to a client and DHCPv4 communicates only the IPv4 address to the device.

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4
Q

DHCP Automatic Allocation

A

DHCPv4 automatically assigns a static IPv4 address permanently to a device selected from a pool of available addresses.; no leases

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5
Q

DHCP Dynamic Allocation

A

Dynamically assigns (leases) an IPv4 address from a pool of addresses for a limited period of time or until the client no longer needs the address.

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6
Q

DHCPv4 Lease Origination Process

A
  1. DHCPDISCOVER - DHCP Discover
  2. DHCPOFFER - DHCP Offer
  3. DHCPREQUEST - DHCP Request
  4. DHCPACK - DHCP Acknowledgement
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7
Q

DHCPv4 - DHCP Discover Step

A

First step of lease origination where client sends out DHCPDISCOVER message over network to find DHCP servers on network using Layer 2 and Layer 3 broadcast addresses.

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8
Q

DHCPv4 - DHCP Offer Step

A

Second step of lease origination where DHCP server receives DHCPDISCOVER , reserves an available address, and sends DHCPOFFER to client system.

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9
Q

How is a DHCPv4 DHCPOFFER message sent?

A
  1. As a unicast message using the MAC Address of the server as the source and the MAC address of the requesting client as the destination.
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10
Q

DHCPv4 - DHCP Request Step

A

Third step of lease origination where client receives DHCPOFFER and responds with DHCPREQUEST message.

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11
Q

What does a DHCPv4 DHCPREQUEST Message do?

A

Used during Lease Origination and Lease Renewal and acts as a binding acceptance to the selected server as well as an implicit decline to any other DHCP servers that may have made an offer to the client.

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12
Q

DHCPv4 - DHCP Acknowledgement Step

A

Final step of Lease Origination where the DHCP server receives the DHCPREQUEST message from the client and responds with a DHCPACK to finalize the DHCP lease.

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13
Q

What 4 Things Occur during DHCPACK

A
  1. Server verifies the lease with ICMP ping to the newly assigned address to ensure it is not being used.
  2. Creates new ARP entry for client lease.
  3. Replies to client with a unicast DHCPACK message.
  4. Client receives DHCPACK, logs configuration information and performs ARP lookup for its new assigned address; if no reply is detected the address is considered valid and the client begins using it.
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14
Q

DHCPv4 Lease Renewal (2)

A
  1. DHCPREQUEST - DHCP Request

2. DHCPACK - DHCP Acknowledgement

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15
Q

What Protocol Do DHCPv4 Messages Use ?

A

UDP

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16
Q

Client Side Ports for Sending DHCPv4 Messsages.

A 
UDP 68 (source)
UDP 67 (destination)
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17
Q

Server Side Ports for Sending DHCPv4 Messages

A 
UDP 68 (destination)
UDP 67 (source)
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18
Q

Minimums and Maximum # of Default Gateways Definable in DHCPv4

A
  1. One minimum

2. Eight maximum.

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19
Q

Operation (OP) Code Message Field (3)

A

Specifies the type of message.

1= request message

2= reply message.

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20
Q

Hardware Type Message Field (4)

A

Identifies type of hardware used in network; same codes used in ARP messages.

1= Ethernet

15= Frame Relay

20= Serial Line

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21
Q

Hardware Address Length Message Field

A

Specifies the length of the address

22
Q

Hops Message Field

A

Controls the forwarding of messages

Set to 0 by a client before transmitting a request.

23
Q

Transaction Identifier Message Field

A

Used by the client to match the request with replies received from DHCPv4 servers.

24
Q

Seconds Message Field (2)

A

id’s the number of seconds elapsed since the client begain attempting to acquire or renew a lease.

Used by servers to prioritize multiple client requests.

25
Q

Flags Message Field (3)

A
  1. Used by a client that does not know its IPv4 address when it sends a request
  2. Only 1 of 16 bits is used; which is a broadcast flag.
  3. Value of 1 tells DHCPv4 server or relay agent that the reply should be sent as a broadcast.
26
Q

Client IP Address (CIADDR) Message Field (2)

A
  1. Used by client during lease renewal when the address of the client is valid and usable.

2 Not used durring Lease Origination ; client sets to 0 for this phase.

27
Q

Your IP Address (YIADDR) Message Field

A

Used by server to assign an IPv4 address to the client.

28
Q

Server IP Address (SIADDR) Message Field

A

Used by server to identify the address of the server that the client should use for the next step in the bootstrap process, which may or may not be the server sending this reply.

29
Q

Server Identifier DHCPv4 Option

A

Special field used by the sending server which includes its own IPv4 address.

30
Q

Gateway IP Address (GIADDR) Message Field

A

Routes DHCPv4 messages when DHCPv4 relay agents are involved.

31
Q

Client Hardware Address (CHADDR) Message Field

A

Specifies the physical layer of the client.

32
Q

Server Name Message Field (3)

A
  1. Used by server during DHCPOFFER and DHCPACK
  2. Server may optionally put its name in this field.
  3. Can be simple text name or DNS server name.
33
Q

Boot Filename Message Field (2)

A
  1. Optional field used by client to request a particular type of boot file in DHCPDISCOVER message.
  2. Used by server in DHCPOFFER to fully specify a boot file directory and filename.
34
Q

DHCP Options Message Field (3)

A
  1. Holds DHCP Options, including several parameters required for basic DHCP operation.
  2. Variable in length.
  3. Usable by client and server.
35
Q

DHCP Relay Agent

A

Router that forwards address assignment / parameter requests to and from a DHCP server.

36
Q

Troubleshooting DHCPv4

A
  1. Resolve IPv4 address conflicts.
  2. Verify physical connectivity.
  3. Test connectivity with static ip address.
  4. Verify switch port connections
  5. Test DHCPv4 Operation on the same subnet or vlan.
37
Q

Two Methods to Dynamically Address in IPv6

A
  1. Stateless Address Autoconfiguration (SLAAC)

2. Dynamic Host Configuration Protocol for IPv6 (Stateful DHCPv6)

38
Q

Router Solicitation Message

A

Client sent message to router to acquire addressing.

39
Q

Where is a RS Message sent.

A

Multicast address FF02::2

40
Q

Router Advertisement Message

A

Router sent message to client which includes the prefix and prefix length of a local segment that the client uses to create its own IPv6 global unicast address.

41
Q

Where is an RA Message sent.

A

All-Nodes multicast address FF02::1

42
Q

Stateless Address Autoconfiguration Operation

A
  1. PC1 sends Router Solicitation(RS) to the all-routers multicast address (FF02::2) to inform the local IPv6 router it needs an Router Advertisement (RA).
  2. Router 1 receives the RS and responds with the requested RA which includes the prefix and prefix length. RA is sent to all-nodes multicast address FF02::1, with the link-local address of the router as the IPv6 source address.
  3. PC1 receives the RA and uses the 64 bit network prefix to create a global unicast address and uses the link-local address of the router as its default gateway.
  4. PC1 sends an ICMPv6 Neighbor Solicitation message with its own newly created address as the target IPv6 address. If no other devices respond with the Neighbor Advertisement message then the ID is unique and is used by the system.
43
Q

EUI-64

A

Creates the “host portion” (Interface ID) out of its 48 bit MAC address.

44
Q

What happens if the IPv6 ID is determined to be not unique in the network?

A

OS has to create a new one.

45
Q

Duplicate Address Detection

A

Process in IPv6 that uses Neighbor Discover and Neighbor Advertisement to determine if an IPv6 address has been duplicated by a client.

46
Q

Stateless DHCPv6 Option (2)

A

Informs client to use RA information to create IPv6 global unicast address.

M Flag = 0; O Flag=1

47
Q

Stateful DHCPv6 Option (

A

Informs client to use a stateful DHCPv6 server for addressing.

M Flag = 1; O Flag is not used.

48
Q

DHCPv6 Operations (6)

A
  1. DHCPv6 starts with ICMPv6 RA message from router.
  2. When stateless/stateful is indicated by RA then DHCPv6 operation is invoked.

3 Sends DHCPv6 SOLICIT message to reserved IPv6 multicast address all-DHCPv6 servers address FF02::1:2

  1. One or more servers respind with DHCPv6 ADVERTISE unicast message; informs client that the server is available for DHCPv6 service.
  2. Client responds with DHCPv6 REQUEST or INFORMATION-REQUEST message to server depending if it is stateful or stateless.
  3. Server sends DHCPv6 REPLY to client containing requested information.
49
Q

DHCP UDP Ports Used

A
  1. Server to Client ; UDP Destination Port 546

2. Client to Server UDP Destination Port 547

50
Q

DHCPv6 INFORMATION-REQUEST Purpose.

A

Used by DHCPv6 client to request only configuration parameters such as DNS server; Stateless.

Client generated its own IPv6 address from RA message and self-generated IID

51
Q

DHCPv6 REQUEST Purpose

A

Stateful; Message to server to obtain IPv6 address and any other configuration parameters from server.

52
Q

Troubleshoot DHCPv6

A
  1. Resolve address conflicts
  2. Verify allocation method / check M | O Flags
  3. Test with static IPv6 address.
  4. Verify switch port configuration
  5. Test DHCPv6 operation on same subnet or VLAN

Networking II (15 decks)

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