Access-list questions part 1

Question 1

Your boss is learning a CCNA training course, refer to the exhibit. The access list has been configured on the S0/0 interface of router RTB in the outbound direction. Which two packets, if routed to the interface, will be denied? (Choose two)

access-list 101 deny tcp 192.168.15.32 0.0.0.15 any eq telnet
access-list 101 permit ip any any

A. source ip address: 192.168.15.5; destination port: 21
B. source ip address:, 192.168.15.37 destination port: 21
C. source ip address:, 192.168.15.41 destination port: 21
D. source ip address:, 192.168.15.36 destination port: 23
E. source ip address: 192.168.15.46; destination port: 23
F. source ip address:, 192.168.15.49 destination port: 23

Answer: D E

Question 2

Refer to the graphic. It has been decided that PC1 should be denied access to Server. Which of the following commands are required to prevent only PC1 from accessing Server1 while allowing all other traffic to flow normally? (Choose two)

A – Router(config)# interface fa0/0
Router(config-if)# ip access-group 101 out
B – Router(config)# interface fa0/0
Router(config-if)# ip access-group 101 in
C – Router(config)# access-list 101 deny ip host 172.16.161.150 host 172.16.162.163
Router(config)# access-list 101 permit ip any any
D – Router(config)# access-list 101 deny ip 172.16.161.150 0.0.0.255 172.16.162.163 0.0.0.0
Router(config)# access-list 101 permit ip any any

Answer: B C

Question 3

Refer to the exhibit. Why would the network administrator configure RA in this manner?

A. to give students access to the Internet
B. to prevent students from accessing the command prompt of RA
C. to prevent administrators from accessing the console of RA
D. to give administrators access to the Internet
E. to prevent students from accessing the Internet
F. to prevent students from accessing the Admin network

Answer: B

Explanation

Although the access-list is used to “permit” network 10.1.1.0/24 but the best answer here is “to prevent students from accessing the command prompt of RA”. From the picture above, we know that 10.1.1.0/24 is the “Admin” network. This access list is applied to “line vty 0 4″ so it will permit only Telnet traffic from “Admin” to RA while drop all other traffic (because of the implicit “deny all” command at the end of the access list). Therefore we can deduce that it will “prevent students from accessing the command prompt of RA”.

This access list only filters Telnet traffic (because it is applied to vty line) so it will not prevent or allow anyone to access the Internet -> A, D, E are not correct.

C is not correct as this access list allows administrators to access the console of RA.

F is not correct as this access list does not proceed TCP, UDP or IP traffic so the students still access the Admin network.

(Notice that the “command prompt” here implies telnet as telnet is the only way to remotely access RA)

Question 4

A network administrator wants to add a line to an access list that will block only Telnet access by the hosts on subnet 192.168.1.128/28 to the server at 192.168.1.5. What command should be issued to accomplish this task?

A – access-list 101 deny tcp 192.168.1.128 0.0.0.15 192.168.1.5 0.0.0.0 eq 23
access-list 101 permit ip any any
B – access-list 101 deny tcp 192.168.1.128 0.0.0.240 192.168.1.5 0.0.0.0 eq 23
access-list 101 permit ip any any
C – access-list 1 deny tcp 192.168.1.128 0.0.0.255 192.168.1.5 0.0.0.0 eq 21
access-list 1 permit ip any any
D – access-list 1 deny tcp 192.168.1.128 0.0.0.15 host 192.168.1.5 eq 23
access-list 1 permit ip any any

Answer: A

Explanation:

First the question asks to block only Telnet access so the port we have to use is 23 -> C is not correct.

Next we need to block traffic from hosts on the subnet 192.168.1.128/28, which is 192.168.1.128 0.0.0.15 if we convert to wildcard mask (just invert all bits of the subnet mask,from 0 to 1 and from 1 to 0 we will get the equivalent wildcard mask of that subnet mask) -> so B is incorrect

In this case, we have to use extended access list because we need to specify which type of traffic (TCP) and which port (23) we want to block -> so D is incorrect because it uses standard access list.

Question 5

As a network administrator, you have been instructed to prevent all traffic originating on the LAN from entering the R2 router. Which the following command would implement the access list on the interface of the R2 router?

A – access-list 101 in
B – access-list 101 out
C – ip access-group 101 in
D – ip access-group 101 out

Answer: C