Cisco 100-105 Exam

The ip helper-address command does what?

  • A. assigns an IP address to a host
  • B. resolves an IP address from a DNS server
  • C. relays a DHCP request across networks
  • D. resolves an IP address overlapping issue
Answer: Option C.
Explanation: 

When the DHCP client sends the DHCP request packet, it doesn’t have an IP address. So it uses the all-zeroes address, 0.0.0.0, as the IP source address. And it doesn’t know how to reach the DHCP server, so it uses a general broadcast address, 255.255.255.255, for the destination. So the router must replace the source address with its own IP address, for the interface that received the request. And it replaces the destination address with the address specified in the ip helper- address command. The client device’s MAC address is included in the payload of the original DHCP request packet, so the router doesn’t need to do anything to ensure that the server receives this information.

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