Refer in the exhibit. A packet capture indicates that the router is not forwarding the DHCP packets that it receives on interface FastEthernet0/0. Which command needs to be entered in global configuration mode to resolve this issue?
A. ip helper-address
B. ip DHCP relay
C. service DHCP
D. ip forward-protocol
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_dhcp/configuration/15-sy/dhcp-15-sy-book/config-dhcp-server.html
“Prerequisites for Configuring the DHCP Server
Before you configure a Cisco DHCP server, you must understand the concepts documented in the “Overview of the DHCP Server” section.
The Cisco DHCP server and the relay agent are enabled by default. Use the no service dhcp command to disable the Cisco DHCP server and the relay agent and the service dhcp command to reenable the functionality.
Port 67 (the DHCP server port) is closed in the Cisco DHCP/BOOTP default configuration. There are two logical parts to the service dhcp command: service enabled and service running. The DHCP service is enabled by default, but port 67 does not open until the DHCP service is running. If the DHCP service is running, the show ip sockets details or the show sockets detail command displays port 67 as open.
The Cisco DHCP relay agent is enabled on an interface only when you configure the ip helper-address command. This command enables a DHCP broadcast to be forwarded to the configured DHCP server.”
I can’t believe people are still debating this.
C.
The Cisco IOS DHCP server and relay agent are enabled by default. You can verify if they have been disabled by checking your configuration file. If they have been disabled, the no service dhcp command will appear in the configuration file. Use the service dhcp command to reenable the functionality if necessary.
C is the correct answer.
Prerequisites for Configuring the Cisco IOS DHCP Relay Agent
Before you configure the DHCP relay agent, you should understand the concepts documented in the “DHCP Overview” module.
The Cisco IOS DHCP server and relay agent are enabled by default. You can verify if they have been disabled by checking your configuration file. If they have been disabled, the no service dhcp command will appear in the configuration file. Use the service dhcp command to reenable the functionality if necessary.
https://www.cisco.com/en/US/docs/ios/12_4t/ip_addr/configuration/guide/htdhcpre.html#wp1096452
Answer is B. The complete command should be:
ip dhcp relay information trust-all
Final answer is C
A. ip helper-address # Cisco router implementation of the DHCP relay agent is provided via the ip helper-address interface configuration command. #To enable forwarding of User Datagram Protocol (UDP) broadcasts, including Bootstrap Protocol (BOOTP), received on an interface, use the ip helper-address command in interface configuration mode.
B. ip DHCP relay #Not a complete command “ip dhcp relay information option”
Enables the system to insert the DHCP relay agent information option (option-82 field) in forwarded BOOTREQUEST messages to a DHCP server.
C. service DHCP #Enabled by default. If it is disable, then enable by issuing “service dhcp”
D. ip forward-protocol #To specify which protocols and ports the router forwards when forwarding broadcast packets
correct answer is D, if not entered ip forward-protocol dhcp will’t be work at all
To specify which protocols and ports the router forwards when forwarding broadcast packets, use the ip forward-protocol command in global configuration mode.
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/command/iap-cr-book/iap-i1.html#wp1776761080
actually, the command “ip dhcp relay” can be configured both globally and on the interface. I have tried on GNS3
Correct answer is C. Agree with RED1.
a and b are performed on interface mode. c is the only one.
Answer: B
https://www.cisco.com/en/US/docs/ios/12_4t/ip_addr/configuration/guide/htdhcpre.html
Agree with RED1. The question specifically states GLOBAL config.
GOOD ASWER IS C:
pay attention,
ip helper-address is in interface configuration mode
The question concerns a global configuration command.
If a no service DHCP command was entered, the dhcp relay agent is disabled, that means your ip helper is not fonctionning.
You have to enable service dhcp so that it will fonction again.
When service dhcp is enabled, the interface command ip helper-address will enable your dhcp relay agent.