9. DHCP, NAT, Mobile IP Flashcards by Julia Delgado Placido

What is DHCP?

Dynamic Host Configuration Protocol is an application layer program that assigns and manages IPs to devices connected on the network.

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What paradigm does DHCP use?

Client-Server Paradigm where the client requests to the DHCP host an IP to be assigned to itself.

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Can DHCP be configured only for routers?

False, it can be assigned to hosts too.

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What can ISP customers do with IP addresses?

Share IP addresses assuming they do not use the Internet at the same time.

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What additional information does a computer need besides its IP address?

The network prefix (or address mask).

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What are two additional addresses most computers need?

Address of the gateway
Domain name server

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What is the role of a DHCP server in a network?

Responsible for configuration of the network

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What action does a client take to request an IP address?

Broadcasts a request using a DHCP DISCOVER packet

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What must happen to the DHCP DISCOVER packet?

It must reach the DHCP server

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What happens if the DHCP server is not directly attached to the network?

The gateway relays DHCP broadcasts to the server

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Fill in the blank: A client broadcasts a request for an IP address using a _______.

DHCP DISCOVER packet

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True or False: A DHCP server can be located anywhere as long as the DHCP DISCOVER packet reaches it.

True

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What is the function of the gateway in relation to DHCP?

Configured to receive and relay DHCP broadcasts

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What does a server do when it receives a request in DHCP?

It allocates a free IP address and sends it to the host in a DHCP OFFER packet

The DHCP OFFER packet may be relayed via the router.

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How does a DHCP server identify a host that does not have an IP address?

Using its Ethernet address carried in the DHCP DISCOVER packet

This allows the server to identify hosts even without assigned IP addresses.

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What is the duration for which IP address assignments are made in DHCP?

For a fixed period of time, called leasing.

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What must a host do just before the DHCP lease expires?

Ask for a DHCP renewal.

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What does the client do after receiving DHCP Offers?

The client selects one of the offers based on certain criteria, such as the first offer received.

Criteria for selection can include factors like offer speed or server preference.

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What message does the client broadcast to indicate acceptance of a DHCP offer?

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The client broadcasts a DHCP Request message.

This message is crucial for the DHCP process as it finalizes the selection.

What is the purpose of the DHCP Request message besides indicating acceptance?

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It serves as a notification to other DHCP servers that their offers were declined.

This helps in managing the offers made by multiple DHCP servers.

What type of message does the selected DHCP server send to confirm that the client can use the assigned IP address?

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DHCP Acknowledgment (ACK) message

The ACK message contains the same configuration parameters as the DHCP OFFER.

What does the DHCP Acknowledgment (ACK) message confirm for the client?

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The client can use the assigned IP address

The client can configure its network interface with the received parameters.

What happens if the DHCP server cannot allocate the requested IP address?

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The server sends a DHCP Negative Acknowledgment (NAK) message

This message prompts the client to restart the DHCP process.

What is the purpose of the DHCP Negative Acknowledgment (NAK) message?

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To prompt the client to restart the process

This occurs if there is an issue or conflict preventing IP address allocation.

Fill in the blank: The selected DHCP server responds with a _______ message.

DHCP Acknowledgment (ACK) message

What does the client do after receiving the DHCP Acknowledgment (ACK) message?

Configures its network interface with the received parameters ## Footnote This is the next step after the ACK message confirmation.

What must the client do before the lease expires?

Renew the lease to continue using the assigned IP address. ## Footnote This process ensures that the client retains its IP address without interruption.

What does the client send to the server to renew the lease?

A DHCP Request directly to the server that granted the lease. ## Footnote This request is essential for maintaining the current IP address.

What does the server respond with if it is available?

A DHCP ACK, extending the lease. ## Footnote The DHCP ACK confirms the extension of the lease period for the IP address.

What happens if the server is not available during the lease renewal?

The client will attempt to contact any available DHCP server to get a new lease. ## Footnote This ensures that the client can still obtain an IP address even if the original server is down.

What message does the client send to release the assigned IP address?

DHCP Release message. ## Footnote This message is sent when the client no longer needs the IP address, allowing it to be returned to the pool for other devices.

What is a magic cookie?

A number used by the server in the format of an IP address.

What is the specific value of the magic cookie mentioned?

99.130.83.99.

What does the magic cookie indicate?

It shows the beginning of the optional data.

If present, how many bytes are designated for options after the magic cookie?

60 bytes.

Fill in the blank: The server uses a magic cookie in the format of an _______.

[IP address]

What are three fields of a DHCP option?

A 1-byte tag field A 1-byte length field A variable length value field

If the tag field in a DHCP option is 53, what are the 8 message types?

DISCOVER OFFER REQUEST DECLINE ACK NACK RELEASE INFORM

What are DHCP messages encapsulated in?

UDP Datagrams, which are also which are encapsulated within IP packets, which are encapsulated within datalink frames.

How does Network Address Translation (NAT) work?

Each home or business is assigned an IP. Within this network, every computer gets a unique local IP which is used for internal traffic. As a packet exits the network, it undergoes address translation where the local IP is converted into the shared public IP

What are the three local IP address ranges?

10.0.0.0 - 10.255.255.255/8 172.16.0.0 - 172.16.255.255/12 192.168.0.0 - 192.168.255.255/16

Where does NAT take place?

NAT box that is located at the gateway of the network.

What is a NAT translation table?

Maps local IPs to global IPs

What mapping is NAT?

Many to one

Does it NAT violate that every IP address is unique?

True

Does NAT violate the end-to-end connectivity model?

True, since the model states that any host can send a packet to any other host but since the NAT box is set up by outgoing packets, incoming packet cannot be accepted until after outgoing packets are sent.

Does NAT change the internet from a connectionless network to connection-oriented?

True

9. DHCP, NAT, Mobile IP Flashcards

(47 cards)