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DHCP and joining a network

What happens when a device connects: DHCP and its four messages, the lease, reservation, relay, then ARP and DNS before the first page.

  • 42 cards
  • 3 topics
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The outline, topic by topic

Each topic is weighted the way the exam weighs it.

  1. The four messages
  2. Lease and reservations
  3. Joining a network

A few cards from the deck

  • What is DHCP?

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    The protocol that automatically gives a device its IP address, mask, gateway and DNS servers.

    Without it, every device would need manual configuration.

  • A computer shows the address 169.254.12.7. Diagnosis?

    • DNS is down
    • The address is perfectly normal
    • The visited site is blocked
    • No DHCP server answered: server down, cable, virtual network or relay
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    No DHCP server answered: server down, cable, virtual network or relay

    That range is the one a device gives itself for lack of a DHCP answer.

  • Short or long leases?

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    Short: addresses free up fast, ideal for transient places, but more renewals. Long: stable for an office, but the pool runs out fast with heavy turnover.

    Lease length sets both how fast addresses recycle and how much you depend on the DHCP server.

  • Getting an address through DHCP: after “Broadcast DHCPDISCOVER”, what is the next message?

    • DHCPREQUEST: I take 192.168.1.42
    • DHCPACK: 24 h lease, gateway and DNS
    • Renewal DHCPREQUEST halfway through the lease
    • DHCPOFFER: 192.168.1.42 offered
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    DHCPOFFER: 192.168.1.42 offered

    The server offers a free address from its pool.

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