Refer to the topology below and answer the questions.
Question 1
Examine the DHCP configuration between R2 and R3, R2 is configured as the DHCP server and R3 as the client. What is the reason R3 is not receiving the IP address via DHCP?
A. On R3, DHCP is not enabled on the interface that is connected to R2.
B. On R3, the interface that is connected to R2 is in shutdown condition.
C. On R2, the interface that is connected to R3 is in shutdown condition.
D. On R2, the network statement in the DHCP pool configuration is incorrectly configured.
Answer: A
Explanation
First we should check which interface on R3 that is connected to R2 via the “show run” command.
From the description we learn interface E0/1 is connected to R2. Use the “show ip interface brief” command to verify the IP address of this interface.
Therefore we can conclude this interface does not have any IP address and there is no configuration on this interface (except the “description Link to R2” line).
If R3 wants to receive an IP address from R2 via DHCP, interface E0/1 should be configured with the command “ip address dhcp” so the answer “DHCP is not enabled on this interface” is correct.
Question 2
R1 router clock is synchronized with ISP router. R2 is supposed to receive NTP updates from R1. But you observe that R2 clock is not synchronized with R1. What is the reason R2 is not receiving NTP updates from R1?
A. R1 router Ethernet interface that is connected to R2 is placed in shutdown condition.
B. R2 router Ethernet interface that is connected to R1 is placed in shutdown condition.
C. The NTP server command not configured on R2 router.
D. The IP address that is used in the NTP configuration on R2 router is incorrect.
Answer: D
Explanation
First we should verify if the ports connected between R1 and R2 is in “up/up” state with the “show ip interface brief” command on R1 & R2.
Note: We learn R1 & R2 connect to each other via E0/2 interface because the IP addresses of these interfaces belong to 192.168.10.0/30 subnet. Both of them are “up/up” so the link connecting between R1 & R2 is good.
Next we need to verify the ntp configuration on R2 with the “show running-config” command.
So there is only one command related to NTP configuration on R2 so we need to check if the IP address of 192.168.100.1 is correct or not. But from the “show ip interface brief” command on R1 we don’t see this IP -> This IP address is not correct. It should be 192.168.10.1 (IP address of interface E0/2 of R1), not 192.168.100.1.
Question 3
Why applications that are installed on PC’s in R2 LAN network 10.100.20.0/24 are unable to communicate with Server1?
A. A standard ACL statement that is configured on R1 is blocking the traffic sourced from R2 LAN network.
B. A standard ACL statement that is configured on R1 is blocking the traffic sourced from Server1 network.
C. A standard ACL statement that is configured on R2 is blocking the traffic sourced from Server1 network.
D. A standard ACL statement that is configured on R2 is blocking the traffic sourced from R2 LAN network.
Answer: C
Explanation
We should check if we can ping from R1 to Server 1 or not:
The ping worked well so maybe R1 is good so we should check R2 first. We notice on R2 there is an access-list:
This access-list is applied to E0/2 interface with inbound direction. The purpose of this access-list is to block traffic with source IP address of 172.16.200.0/24 so it will block all traffic sent from Server 1 to us.
Question 4
Users complain that they are unable to reach internet sites. You are troubleshooting internet connectivity problem at main office. Which statement correctly identifies the problem on Router R1?
A. NAT configurations on the interfaces are incorrectly configured.
B. NAT translation statement incorrectly configured.
C. Interesting traffic for NAT ACL is incorrectly configured.
D. Only static NAT translation configured from the server, missing Dynamic NAT or Dynamic NAT overloading for internal networks.
Answer: A
Explanation
If all users cannot access internet then R1 is most likely to cause the problem so we should check it first. From the “show running-config” command we will see:
We notice that interface E0/0 (connected to ISP) has been configured as “nat inside” while interfaces E0/1 & E0/2 (connected to our company) have been configured as “nat outside”. This is not correct because “nat inside” should be configured with interfaces connected to our company while “nat outside” should be configured with interfaces connected to the internet. Therefore we can conclude the NAT configuration on these interfaces is not correct.
Question 1
Examine the DHCP configuration between R2 and R3, R2 is configured as the DHCP server and R3 as the client. What is the reason R3 is not receiving the IP address via DHCP?
A. On R3, DHCP is not enabled on the interface that is connected to R2.
B. On R3, the interface that is connected to R2 is in shutdown condition.
C. On R2, the interface that is connected to R3 is in shutdown condition.
D. On R2, the network statement in the DHCP pool configuration is incorrectly configured.
Answer: A
Explanation
First we should check which interface on R3 that is connected to R2 via the “show run” command.
From the description we learn interface E0/1 is connected to R2. Use the “show ip interface brief” command to verify the IP address of this interface.
Therefore we can conclude this interface does not have any IP address and there is no configuration on this interface (except the “description Link to R2” line).
If R3 wants to receive an IP address from R2 via DHCP, interface E0/1 should be configured with the command “ip address dhcp” so the answer “DHCP is not enabled on this interface” is correct.
Question 2
R1 router clock is synchronized with ISP router. R2 is supposed to receive NTP updates from R1. But you observe that R2 clock is not synchronized with R1. What is the reason R2 is not receiving NTP updates from R1?
A. R1 router Ethernet interface that is connected to R2 is placed in shutdown condition.
B. R2 router Ethernet interface that is connected to R1 is placed in shutdown condition.
C. The NTP server command not configured on R2 router.
D. The IP address that is used in the NTP configuration on R2 router is incorrect.
Answer: D
Explanation
First we should verify if the ports connected between R1 and R2 is in “up/up” state with the “show ip interface brief” command on R1 & R2.
Note: We learn R1 & R2 connect to each other via E0/2 interface because the IP addresses of these interfaces belong to 192.168.10.0/30 subnet. Both of them are “up/up” so the link connecting between R1 & R2 is good.
Next we need to verify the ntp configuration on R2 with the “show running-config” command.
So there is only one command related to NTP configuration on R2 so we need to check if the IP address of 192.168.100.1 is correct or not. But from the “show ip interface brief” command on R1 we don’t see this IP -> This IP address is not correct. It should be 192.168.10.1 (IP address of interface E0/2 of R1), not 192.168.100.1.
Question 3
Why applications that are installed on PC’s in R2 LAN network 10.100.20.0/24 are unable to communicate with Server1?
A. A standard ACL statement that is configured on R1 is blocking the traffic sourced from R2 LAN network.
B. A standard ACL statement that is configured on R1 is blocking the traffic sourced from Server1 network.
C. A standard ACL statement that is configured on R2 is blocking the traffic sourced from Server1 network.
D. A standard ACL statement that is configured on R2 is blocking the traffic sourced from R2 LAN network.
Answer: C
Explanation
We should check if we can ping from R1 to Server 1 or not:
The ping worked well so maybe R1 is good so we should check R2 first. We notice on R2 there is an access-list:
This access-list is applied to E0/2 interface with inbound direction. The purpose of this access-list is to block traffic with source IP address of 172.16.200.0/24 so it will block all traffic sent from Server 1 to us.
Question 4
Users complain that they are unable to reach internet sites. You are troubleshooting internet connectivity problem at main office. Which statement correctly identifies the problem on Router R1?
A. NAT configurations on the interfaces are incorrectly configured.
B. NAT translation statement incorrectly configured.
C. Interesting traffic for NAT ACL is incorrectly configured.
D. Only static NAT translation configured from the server, missing Dynamic NAT or Dynamic NAT overloading for internal networks.
Answer: A
Explanation
If all users cannot access internet then R1 is most likely to cause the problem so we should check it first. From the “show running-config” command we will see:
We notice that interface E0/0 (connected to ISP) has been configured as “nat inside” while interfaces E0/1 & E0/2 (connected to our company) have been configured as “nat outside”. This is not correct because “nat inside” should be configured with interfaces connected to our company while “nat outside” should be configured with interfaces connected to the internet. Therefore we can conclude the NAT configuration on these interfaces is not correct.
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