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Zorluk: OrtaDHCP Server, Client, and Relay Agent Operation and Configuration

A host connected to VLAN 100 (10.100.1.0/2410.100.1.0/24) broadcasts a DHCPDISCOVER packet to obtain network parameters. The client-facing gateway interface GigabitEthernet0/0/0.100 (10.100.1.1/2410.100.1.1/24) on router R1 is configured with the command `ip helper-address 192.168.50.10`. Which operation does router R1 perform upon receiving this broadcast?

  1. R1 inserts its GigabitEthernet0/0/0.100 IP address (10.100.1.110.100.1.1) into the `giaddr` field and forwards the request as a unicast packet to 192.168.50.10192.168.50.10.Cevap
  2. B
    R1 inserts the IP address of its egress interface facing the DHCP server into the `giaddr` field and unicasts the packet to 192.168.50.10192.168.50.10.
  3. C
    R1 floods the original DHCPDISCOVER broadcast packet out all active interfaces except GigabitEthernet0/0/0.100.
  4. D
    R1 replaces the broadcast destination IP address (255.255.255.255255.255.255.255) with 192.168.50.10192.168.50.10 while preserving the broadcast MAC address.

Cevap

Router R1 inserts the IP address of its client-facing interface (10.100.1.110.100.1.1) into the `giaddr` field of the DHCP payload and forwards the request as a unicast packet to the configured relay destination 192.168.50.10192.168.50.10.
When a router configured with `ip helper-address` receives a broadcast DHCPDISCOVER packet on a client-facing interface, it acts as a DHCP relay agent. It populates the `giaddr` (gateway IP address) field in the DHCP header with the IP address assigned to the receiving ingress interface (10.100.1.110.100.1.1). This critical step enables the remote DHCP server to select an IP address from the matching IP pool subnet. The router then converts the broadcast frame into a unicast IP packet addressed directly to the helper address (192.168.50.10192.168.50.10).

Adım Adım Çözüm

1
Analyze the incoming DHCPDISCOVER request on the client-facing gateway interface.
The host sends a layer 2 broadcast (FF:FF:FF:FF:FF:FFFF:FF:FF:FF:FF:FF) and layer 3 broadcast (255.255.255.255255.255.255.255) requesting an address assignment on VLAN 100.
DHCP clients initially have no IP address and must discover servers via broadcasting.
2
Evaluate the relay agent processing mechanism invoked by `ip helper-address`.
Router R1 intercepts the UDP broadcast port 67 packet, inserts 10.100.1.110.100.1.1 into the `giaddr` (Gateway IP Address) field of the DHCP message header, and sets the destination IP to 192.168.50.10192.168.50.10.
The `giaddr` field informs the remote DHCP server which subnet IP pool must be drawn from to serve the client.
3
Determine packet forwarding mechanics across the network core.
R1 routes the modified request as a standard unicast packet to 192.168.50.10192.168.50.10.
Unicast routing allows the DHCP request to cross multiple routed hops to reach a centralized server.

Anahtar Kavram

DHCP Relay Agent Operation and Gateway IP Address (`giaddr`) Insertion
Tahmini Süre:1m 15s
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DHCP Server, Client, and Relay Agent Operation and Configuration

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