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

A network administrator needs to enable DHCP relay functionality on a Cisco IOS router so that hosts located in VLAN 40 (10.40.0.0/2410.40.0.0/24) can receive dynamic IP addresses from a centralized DHCP server located at 192.168.100.50192.168.100.50 in the management network. Subinterface GigabitEthernet0/0/0.40 serves as the default gateway for VLAN 40, while GigabitEthernet0/0/1 connects directly to the core switch leading to the DHCP server. On which interface must the administrator execute the `ip helper-address 192.168.100.50` command?

  1. Subinterface GigabitEthernet0/0/0.40Cevap
  2. B
    Interface GigabitEthernet0/0/1
  3. C
    Global configuration mode
  4. D
    Both GigabitEthernet0/0/0.40 and GigabitEthernet0/0/1

Cevap

Subinterface GigabitEthernet0/0/0.40 is the correct interface for configuring the helper address.
DHCP DISCOVER and REQUEST messages are sent as Local Subnet Broadcasts (255.255.255.255255.255.255.255). To forward these requests across network boundaries to a remote DHCP server, the router must intercept the broadcast at the client's default gateway interface. Therefore, `ip helper-address` must be applied to subinterface GigabitEthernet0/0/0.40, which inspects incoming broadcasts, inserts its IP address into the `giaddr` field, and unicasts the request to 192.168.100.50192.168.100.50.

Adım Adım Çözüm

1
Identify the ingress boundary for client broadcast traffic
Hosts on VLAN 40 send DHCP DISCOVER broadcasts to their default gateway at subinterface GigabitEthernet0/0/0.40.
Routers block broadcast traffic by default. The DHCP relay agent listens for incoming UDP broadcasts on the specific client gateway interface.
2
Apply the IP helper address configuration
Entering `ip helper-address 192.168.100.50` under interface configuration mode for subinterface GigabitEthernet0/0/0.40 enables broadcast-to-unicast conversion.
This sets the Gateway IP Address (giaddr) field to the subinterface IP address and forwards the unicast packet to the centralized DHCP server.

Anahtar Kavram

DHCP Relay Agent Interface Configuration
Tahmini Süre:1m 30s
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Konular

DHCP Server, Client, and Relay Agent Operation and Configuration

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