Refer to the exhibit. Router R1 is being used as a relay device for autoconfiguration of switch
S1. Which configuration will accomplish this?
Select the best response.
A.
S1(config)# interface fastethernet 0/1
S1(config-if)# ip helper-address 10.0.0.2
B.
S1(config)# interface fastethernet 0/1
S1(config-if)# ip helper-address 20.0.0.1
C.
R1(config)# interface fastethernet 0/0
R1(config-if)# ip helper-address 20.0.0.2
R1(config-if)# ip helper-address 20.0.0.3
R1(config-if)# ip helper-address 20.0.0.4
R1(config-if)# exit
R1(config)# interface fastethernet 0/1
R1(config-if)# ip helper-address 10.0.0.1
D.
R1(config)# interface fastethernet 0/0
R1(config-if)# ip helper-address 20.0.0.1
R2(config)# interface fastethernet 0/0
R2(config-if)# ip helper-address 20.0.0.1
R3(config)# interface fastethernet 0/0
R3(config-if)# ip helper-address 20.0.0.1
R4(config)# interface fastethernet 0/0
R4(config-if)# ip helper-address 20.0.0.1
E.
S1(config)# interface fastethernet 0/1
S1(config-if)# ip helper-address 10.0.0.2
R2(config)# interface fastethernet 0/0
R2(config-if)# ip helper-address 20.0.0.1
R3(config)# interface fastethernet 0/0
R3(config-if)# ip helper-address 20.0.0.1
R4(config)# interface fastethernet 0/0
R4(config-if)# ip helper-address 20.0.0.1
Explanation:
The point of this question is about the command “ip helper-address”.
The ip helper-address command allows you to forward broadcast to unicast. One common
application that requires helper addresses is Dynamic Host Configuration Protocol (DHCP).
All of the following conditions must be met in order for a UDP or IP packet to be helpered by
the ip helper-address command:
1. The MAC address of the received frame must be all-ones broadcast address (ffff.ffff.ffff).
2. The IP destination address must be one of the following: all-ones broadcast
(255.255.255.255), subnet broadcast for the receiving interface; or major-net broadcast for
the receiving interface if the no ip classless command is also configured.
3. The IP time-to-live (TTL) value must be at least 2.
4. The IP protocol must be UDP (17).
5. The UDP destination port must be for TFTP, Domain Name System (DNS), Time,
NetBIOS, ND, BOOTP or DHCP packet, or a UDP port specified by the ip forward-protocol
udp global configuration command.
From this question, we will find the configuration must be done in CK-R1 which is the relay.