Exam 350-401 topic 1 question 772 discussion

I know A, B and D are wrong so i eliminated those answers and C is the result.

It's C. Cisco devices typically reject DHCP packets with zero giaddr (gateway IP address) when DHCP snooping is enabled. This can cause issues in certain network configurations. Here are some examples and solutions: Default Behavior By default, Cisco IOS devices reject DHCP packets with zero giaddr. This is done as a security measure to prevent potential DHCP spoofing attacks. Common Scenarios 1. DHCP Snooping on Access Switches: When DHCP snooping is enabled on Cisco Catalyst switches, they often use a giaddr of zero. This conflicts with the default behavior of Cisco DHCP servers. 2. Option 82 Insertion: Switches performing DHCP snooping insert Option 82 into DHCP messages from clients, but don't modify the giaddr field, leaving it as 0.0.0.0 hth

C is the only one makes sinse

With the information available, option C seems to be the most relevant: C. The DHCP server drops DHCP packets carrying Option 82 and an empty relay agent IP address. This is because the DHCP server itself is on the router (as evidenced by the presence of the DHCP pool configuration), and there's no need for an ip helper-address on the local router's interface for DHCP server functionality. The error message indicates an issue with DHCP Option 82, which suggests that the problem lies in how the DHCP server or relay agent is handling the packets, rather than a missing DHCP relay configuration. In practical scenarios, when DHCP snooping is configured on a switch, the switch inserts information into the DHCP packets (Option 82) to indicate where the packets came from. If the DHCP server is not expecting or is not configured to handle Option 82, it may drop the packets, hence the error message about inconsistent relay information. This is consistent with the symptoms described in the debug output provided.

Focus on log DHCPD: relay information option exists, but giaddr is zero giaddr (Gateway IP Address) is a field within DHCP packets used in DHCP relay scenarios. It contains the IP address of the relay agent (gateway) that forwards the DHCP request from a client to the DHCP server. This helps the DHCP server assign appropriate IP addresses and configuration to clients on different subnets. Add giaddr on the interface that perform DHCP. " ip dhcp relay information trusted giaddr_IP " command, you indicate that the relay agent IP address should be included in DHCP packets as they are forwarded to the DHCP server.

Can someone please explain?

Seems to be ok A,B,D - incorrect