DHCP IP Address Allocation
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Questions and Answers

What happens when a client requests an IP address from a DHCP server?

  • The client assigns its own IP address
  • The DHCP server generates a new IP address
  • The DHCP server retrieves it from its storage and delivers it to the client (correct)
  • The DHCP server assigns a permanent IP address to the client

    • Which type of allocation is best suited for giving IP addresses to servers?

  • Static allocation
  • Manual allocation (correct)
  • Automatic allocation
  • Dynamic allocation

    • What is the main advantage of Dynamic allocation?

  • It allows for efficient management of a pool of network addresses (correct)
  • It assigns permanent IP addresses to clients
  • It is the simplest method of allocating IP addresses
  • It ensures that servers have permanent IP addresses

    • What happens when a client's lease expires?

    <p>The client's IP address is released back to the DHCP server</p> Signup and view all the answers

    What is the purpose of a lease in Dynamic allocation?

    <p>To allow the client to use the IP address for a limited period of time</p> Signup and view all the answers

    What is the purpose of the DHCPREQUEST message sent by the client?

    <p>To renew the lease of the current address</p> Signup and view all the answers

    What happens if the client does not receive an answer from the DHCP server until time2 has passed?

    <p>It enters the REBINDING state and sends a multicast message to all servers</p> Signup and view all the answers

    What can a client do when its lease is about to expire?

    <p>Extend its lease with subsequent requests</p> Signup and view all the answers

    What is the default value of time1?

    <p>Half of the lease time of the current address</p> Signup and view all the answers

    What is an advantage of using Dynamic allocation in a network with limited addresses?

    <p>It allows for efficient management of a pool of network addresses</p> Signup and view all the answers

    What is the main difference between Dynamic and Manual allocation?

    <p>Dynamic allocation assigns temporary IP addresses, while Manual allocation assigns permanent IP addresses</p> Signup and view all the answers

    What happens if the client gets a new address but not its previous address?

    <p>It continues to work, but not with the current web parameters, and must inform the users about this</p> Signup and view all the answers

    What is the purpose of the DHCP server?

    <p>To supply DHCP clients with the configuration parameters defined in the Host Requirements RFCs</p> Signup and view all the answers

    What does a client do with its IP address when it no longer needs it?

    <p>It releases the IP address back to the DHCP server</p> Signup and view all the answers

    What is the shortest waiting time before sending DHCPREQUEST again?

    <p>One minute</p> Signup and view all the answers

    What is the primary task of a DHCP server?

    <p>To provide a permanent storage of network parameters for network clients</p> Signup and view all the answers

    What is the format of the DHCP storage model?

    <p>A per-host list of entries of the form: key = value</p> Signup and view all the answers

    What happens if the client gets its previous address?

    <p>It continues to work normally</p> Signup and view all the answers

    How does a client request its configuration parameters from a DHCP server?

    <p>By sending a request message to the server</p> Signup and view all the answers

    What is the default value of time2?

    <p>0.875x(lease time)</p> Signup and view all the answers

    What is the purpose of the options field in a DHCP response message?

    <p>To carry the configuration parameters for the client</p> Signup and view all the answers

    What happens if the client does not get an address at all?

    <p>It stops its work and goes back to INIT state</p> Signup and view all the answers

    What is the advantage of using default values defined in the Host Requirements RFCs?

    <p>To reduce the number of parameters delivered from the server to the client</p> Signup and view all the answers

    What is the purpose of the parameter request list option?

    <p>To allow clients to request only those parameters required by the client</p> Signup and view all the answers

    What is the basis of the DHCP message format?

    <p>The format of BOOTP messages</p> Signup and view all the answers

    Why is the DHCP message format based on BOOTP messages?

    <p>To ensure compatibility with BOOTP relay agents and BOOTP clients</p> Signup and view all the answers

    What is the purpose of the DHCP protocol?

    <p>To provide a dynamic configuration of network parameters for network clients</p> Signup and view all the answers

    What is the purpose of the 'xid' field in a DHCP message?

    <p>To associate the request message with its response</p> Signup and view all the answers

    What is the length of the 'hlen' field in a DHCP message?

    <p>1 byte</p> Signup and view all the answers

    What is the purpose of the 'ciaddr' field in a DHCP message?

    <p>To specify the client's IP address</p> Signup and view all the answers

    What is the length of the 'chaddr' field in a DHCP message?

    <p>16 bytes</p> Signup and view all the answers

    What is the purpose of the 'hops' field in a DHCP message?

    <p>Optionally used by relay agents when booting via a relay agent</p> Signup and view all the answers

    What is the purpose of the 'flags' field in a DHCP message?

    <p>Flags</p> Signup and view all the answers

    What is the purpose of the 'yiaddr' field in a DHCP message?

    <p>To specify the 'your' IP address</p> Signup and view all the answers

    What is the length of the 'sname' field in a DHCP message?

    <p>64 bytes</p> Signup and view all the answers

    What is the purpose of the 'siaddr' field in a DHCP message?

    <p>To specify the server's IP address</p> Signup and view all the answers

    What is the first message sent by the DHCP client in the client-server negotiation process?

    <p>DHCPDISCOVER</p> Signup and view all the answers

    What is the purpose of the DHCPREQUEST message?

    <p>To select one server from which to request configuration parameters</p> Signup and view all the answers

    What happens when the client receives a DHCPNAK message?

    <p>The client restarts the configuration process</p> Signup and view all the answers

    What is the role of the DHCPOFFER message?

    <p>To offer configuration parameters to the client</p> Signup and view all the answers

    How many servers can be selected by the client in the DHCP negotiation process?

    <p>Only one server</p> Signup and view all the answers

    What is the purpose of the DHCPRELEASE message?

    <p>To relinquish the lease on a network address</p> Signup and view all the answers

    What is the final message sent by the server in the DHCP negotiation process?

    <p>DHCPACK</p> Signup and view all the answers

    What happens when the server receives a DHCPRELEASE message?

    <p>The server marks the lease as free</p> Signup and view all the answers

    What is the purpose of the DHCPACK message?

    <p>To commit the configuration parameters</p> Signup and view all the answers

    What happens when a DHCP client sends a request to a non-authoritative server?

    <p>The server ignores the request, leading to an implementation-dependent time out for the client</p> Signup and view all the answers

    What is the purpose of the DHCPOFFER message?

    <p>To reserve an IP address for the client and send an offer</p> Signup and view all the answers

    What happens when the client receives a DHCPOFFER message?

    <p>The client broadcasts a DHCPREQUEST message to all servers</p> Signup and view all the answers

    What information is included in the DHCPOFFER message?

    <p>The client's MAC address, IP address, subnet mask, lease duration, and server's IP address</p> Signup and view all the answers

    What is the purpose of the DHCPREQUEST message?

    <p>To accept an offer made by the DHCP server</p> Signup and view all the answers

    What is the final phase of the configuration process?

    <p>The DHCP acknowledgement phase</p> Signup and view all the answers

    What happens when a client's IP lease is still valid on a different subnet?

    <p>The client may request its last-known IP address.</p> Signup and view all the answers

    Which type of server may grant a client's request for its last-known IP address?

    <p>Authoritative server</p> Signup and view all the answers

    What is the purpose of a client's broadcast in the DHCP discovery phase?

    <p>To find available DHCP servers.</p> Signup and view all the answers

    What may a client start after obtaining an IP address to prevent IP conflicts?

    <p>An address resolution query.</p> Signup and view all the answers

    Which UDP port is used by the DHCP client side?

    <p>68/udp</p> Signup and view all the answers

    What is the destination of a client's UDP packet in the DHCP discovery phase?

    <p>255.255.255.255</p> Signup and view all the answers

    What is the primary purpose of a DHCPINFORM request message?

    <p>To obtain local configuration parameters without allocating a new address</p> Signup and view all the answers

    What happens when a client reuses a previously allocated network address?

    <p>The client includes its network address in the 'requested IP address' option</p> Signup and view all the answers

    What is the purpose of a DHCPOFFER message?

    <p>To offer configuration parameters to the client</p> Signup and view all the answers

    What message is sent by the client to locate available DHCP servers?

    <p>DHCPDISCOVER</p> Signup and view all the answers

    What is the purpose of the DHCPREQUEST message?

    <p>To decline offers from all other servers</p> Signup and view all the answers

    What is the response sent by the server when a client reuses a previously allocated network address?

    <p>DHCPACK</p> Signup and view all the answers

    What is the purpose of the DHCPDISCOVER message?

    <p>To locate available DHCP servers</p> Signup and view all the answers

    What is the response sent by the server when a client sends a DHCPINFORM request message?

    <p>DHCPACK</p> Signup and view all the answers

    Study Notes

    DHCP Allocation Methods

    • There are three methods of DHCP allocation: Manual, Automatic, and Dynamic allocation.
    • Manual allocation is best suited for giving IP addresses to servers, as it guarantees a permanent and known location in the network.
    • Dynamic allocation is the most interesting method, as it involves assigning, reclaiming, and reusing network addresses.
    • It's useful in cases where there is a limited amount of network addresses, and computers temporarily connect and disconnect to the network.

    Dynamic Allocation

    • The client requests a network address for a limited period of time (lease).
    • The DHCP server allocates an address, marks it as 'used', and notifies the client about the address and lease time.
    • The client can extend its lease, ask for a permanent assignment, or release the address back to the server before the lease expires.

    Renewing and Acquiring Addresses

    • The client holds two times in its memory: time1 and time2.
    • Time1 is when the client starts to ask its server for renewing the lease, and time2 is when the client starts to ask other servers for an address.
    • If the client doesn't get an answer, it waits half of the time left before sending DHCPREQUEST again.
    • The shortest waiting time is one minute.

    Configuration Parameters Delivery

    • The DHCP server supplies clients with configuration parameters defined in the Host Requirements RFCs.
    • The server provides a permanent storage of network parameters for clients.
    • The storage model is a set of key-value pairs for each client, where the key is a unique identifier and the value contains the configuration parameters.

    Message Format

    • The DHCP message format is based on the BOOTP message format.
    • The message format includes fields such as op, htype, hlen, hops, xid, secs, flags, ciaddr, yiaddr, siaddr, giaddr, chaddr, sname, and file.

    Client/Server Model

    • The client and server negotiate in a series of messages to get the parameters the client needs.
    • The client broadcasts a DHCPDISCOVER message, and each server responds with a DHCPOFFER message.
    • The client chooses one server and broadcasts a DHCPREQUEST message, and the selected server responds with a DHCPACK message.

    Steps of Communication

    • The client broadcasts a DHCPDISCOVER message.
    • Each server responds with a DHCPOFFER message.
    • The client chooses one server and broadcasts a DHCPREQUEST message.
    • The selected server responds with a DHCPACK message.
    • The client receives the DHCPACK message and is configured.
    • If the client receives a DHCPNAK message, it restarts the configuration process.
    • The client may choose to relinquish its lease on a network address by sending a DHCPRELEASE message.
    • The server receives the DHCPRELEASE message and marks the lease as free.

    DHCP Fundamentals

    • DHCP (Dynamic Host Configuration Protocol) is a network management protocol used to dynamically assign IP addresses to devices on a network.
    • DHCP automates and centrally manages IP configurations, replacing manual assignments by network administrators.

    DHCP Operations

    • DHCP operations fall into four basic phases: IP lease request, IP lease offer, IP lease selection, and IP lease acknowledgement.

    IP Lease Request

    • A client broadcasts a request for an IP address to available DHCP servers on the local physical subnet.
    • The client can request its last-known IP address, and the server may grant the request if it is still valid.

    IP Lease Offer

    • The DHCP server responds with a DHCPOFFER message containing the client's MAC address, IP address, subnet mask, lease duration, and server's IP address.
    • The server determines the configuration based on the client's hardware address (CHADDR field).

    IP Lease Selection and Acknowledgement

    • The client accepts an offer by broadcasting a DHCPREQUEST message, and other DHCP servers withdraw their offers.
    • The DHCP server responds with a DHCPACK packet, including the lease duration and any other requested configuration information.
    • The TCP/IP configuration process is complete after the client receives the DHCPACK packet.

    DHCP Message Types

    • DHCPDISCOVER: client broadcast to locate available servers
    • DHCPOFFER: server response to DHCPDISCOVER with configuration offer
    • DHCPREQUEST: client message to servers for requesting offered parameters or confirming correctness of previously allocated address
    • DHCPACK: server response to DHCPREQUEST, including lease duration and configuration information

    Additional DHCP Features

    • A client can reuse a previously allocated network address by including it in the 'requested IP address' option in the DHCPREQUEST message.
    • A client can obtain local configuration parameters without allocating a new address using a DHCPINFORM request message.

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    Related Documents

    ch1.pdf

    Description

    Learn about manual and dynamic allocation of IP addresses in DHCP, including its suitability for servers and temporary assignments.

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