Access-list questions part 2

Question 1

The following access list below was applied outbound on the E0 interface connected to the 192.169.1.8/29 LAN:

access-list 135 deny tcp 192.169.1.8 0.0.0.7 eq 20 any
access-list 135 deny tcp 192.169.1.8 0.0.0.7 eq 21 any

How will the above access lists affect traffic?

A – FTP traffic from 192.169.1.22 will be denied
B – No traffic, except for FTP traffic will be allowed to exit E0
C – FTP traffic from 192.169.1.9 to any host will be denied
D – All traffic exiting E0 will be denied
E – All FTP traffic to network 192.169.1.9/29 will be denied

Answer: D

Explanation:

There is always an implicit “deny all” command at the end of every access list, so if an access list doesn’t have any “permit” command, it will block all the traffic. If we use the command “access-list 135 permit ip any any” at the end of this access list then the answer should be C – FTP traffic from 192.169.1.9 to any host will be denied.

Question 2

The access control list shown in the graphic has been applied to the Ethernet interface of router R1 using the ip access-group 101 in command. Which of the following Telnet sessions will be blocked by this ACL? (Choose two)

A – from host PC1 to host 5.1.1.10
B – from host PC1 to host 5.1.3.10
C – from host PC2 to host 5.1.2.10
D – from host PC2 to host 5.1.3.8

Answer: B D

Explanation

Below is the simple syntax of an extended access list:

access-list access-list-number {deny | permit} {ip|tcp|udp|icmp} source [source-mask] dest [dest-mask] [eq dest-port]

Notice that this access list is applied to the Ethernet interface of R1 in the “in direction” so in this case, it will filter all the packets originated from E1 network (host PC1 and PC2) with these parameters:

Source network: 5.1.1.8 0.0.0.3 which means 5.1.1.8/252 (just invert all the wildcard bits to get the equivalent subnet mask) -> Packets from 5.1.1.8 to 5.1.1.11 will be filtered.

Destination network: 5.1.3.0 0.0.0.255 which means 5.1.3.0/24-> Packets to 5.1.3.0/24 will be filtered

Therefore packets originated from 5.1.1.8 to 5.1.1.11 and have the destination to the host 5.1.3.x (via Telnet) will be denied.

Question 3

The following configuration line was added to router R1

Access-list 101 permit ip 10.25.30.0 0.0.0.255 any

What is the effect of this access list configuration?
A – permit all packets matching the first three octets of the source address to all destinations
B – permit all packet matching the last octet of the destination address and accept all source addresses
C – permit all packet matching the host bits in the source address to all destinations
D – permit all packet from the third subnet of the network address to all destinations

Answer: A