Security Questions and Answers

Answer: C

Correct answer: Router# show access-lists

show access-lists displays every list on the router with all its entries and the match counters against each, which is what makes it the first command for checking whether a list is doing what was intended. It is a privileged exec command, so the prompt must show the hash rather than the angle bracket - which is what rules out the user-mode options.

Answer: A

The first thing to check in a question like this is the access-list number. Right away, you can see that the second option is wrong because it is using a standard IP access-list number. The second thing to check is the protocol. If you are filtering by upper-layer protocol, then you must be using either UDP or TCP; this eliminates the fourth option. The third and last answers have the wrong syntax.

Answer: C

Correct answer: show ip interface

show ip interface reports the IP configuration of each interface, including the lines stating which access list is applied inbound and which outbound - so it answers where a list is applied. show access-lists answers the different question of what the lists contain, and neither of the other two commands exists.

Answer: B

Correct answer: 2 and 4

Both refer to exactly one host. The wildcard 0.0.0.0 requires every bit of the address to match, and the host keyword is shorthand for precisely that - IOS accepts either and displays the second form. Option 1 uses 0.0.0.255, which matches the whole 172.16.30.0 subnet, and options 3, 5 and 6 are not valid syntax at all.

Answer: D

The only command that shows which access lists have been applied to an interface is show ip interface Ethernet 0. The command show access-lists displays all configured access lists, and show ip access-lists displays all configured IP access lists, but neither command indicates whether the displayed access lists have been applied to an interface.

Answer: C

The range of 192.168.160.0 to 192.168.191.0 is a block size of 32. The network address is 192.168.160.0 and the mask would be 255.255.224.0, which for an access list must be a wildcard format of 0.0.31.255. The 31 is used for a block size of 32. The wildcard is always one less than the block size.

Answer: B

First, you must know that a /21 is 255.255.248.0, which is a block size of 8 in the third octet. Counting by eight, this makes our subnet 144 in the third octet, and the wildcard for the third octet would be 7 since the wildcard is always one less than the block size.

Answer: C

Correct answer: One access list may be configured, per direction, for each layer 3 protocol configured on an interface.

The limit is one list per protocol per direction per interface - so an interface can carry an inbound and an outbound IP list at once, and separate lists again for any other routed protocol running on it. Needing two IP lists in the same direction means the two sets of rules must be combined into one, which is why the order of entries within a list matters so much.

Answer: C

The extended access list ranges are 100-199 and 2000-2699, so the access-list number of 100 is valid. Telnet uses TCP, so the protocol TCP is valid. Now you just need to look for the source and destination address. Only the third option has the correct sequence of parameters. Answer B may work, but the question specifically states "only" to network 192.168.10.0, and the wildcard in answer B is too broad.

Answer: C

Correct answer: Router(config-if)# ip access-group 110 in

Two things must both be right, and each of the wrong options gets one of them wrong. The command is ip access-group, not ip access-list, since the latter creates a named list rather than applying one; and it is entered in interface configuration mode, because an access list is applied to a particular interface in a particular direction.