Security Questions and Answers

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.

Answer: D

When trying to find the best answer to an access-list question, always check the access-list number and then the protocol. When filtering to an upper-layer protocol, you must use an extended list, numbers 100-199 and 2000-2699. Also, when you filter to an upper-layer protocol, you must use either tcp or udp in the protocol field. If it says ip in the protocol field, you cannot filter to an upper-layer protocol. SMTP uses TCP.

Answer: B

Correct answer: access-list 1 deny 172.16.10.1 0.0.0.0

A standard IP access list is numbered 1 to 99, matches on the source address only, and uses a wildcard mask. This entry satisfies all three, and 0.0.0.0 as a wildcard means every bit must match - equivalent to writing host 172.16.10.1. The 110 example is an extended list, and the option with 255.255.0.0 uses a subnet mask where a wildcard is required.

Answer: C

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

A named list is applied exactly as a numbered one is, with its name in place of the number, from interface configuration mode. The names are case sensitive, so Blocksales must be typed as it was created. Applying the number 110 would reference a different list altogether - and probably one that does not exist.

Answer: D

First, you must know that a /20 is 255.255.240.0, which is a block size of 16 in the third octet. Counting by 16s, this makes our subnet 48 in the third octet, and the wildcard for the third octet would be 15 since the wildcard is always one less than the block size.

Answer: C

Telnet access to the router is restricted by using either a standard or extended IP access list inbound on the VTY lines of the router. The command access-class is used to apply the access list to the VTY lines.

Answer: C

Correct answer: ip access-group 101 in

The list is *created* with access-list in global configuration mode and *applied* with ip access-group in interface configuration mode, naming the list and the direction. Confusing the two commands is the commonest error here, and the direction keyword is not optional - a list applied the wrong way round filters traffic the interface never sees.

Answer: A

First, you must know that a /19 is 255.255.224.0, which is a block size of 32 in the third octet. Counting by 32, this makes our subnet 192 in the third octet, and the wildcard for the third octet would be 31 since the wildcard is always one less than the block size.

Answer: D

Extended IP access lists use numbers 100-199 and 2000-2699 and filter based on source and destination IP address, protocol number, and port number. The last option is correct because of the second line that specifies permit ip any any. (I used 0.0.0.0 255.255.255.255, which is the same as the any option.) The third option does not have this, so it would deny access but not allow everything else.