Security problems
- 1. If you wanted to deny FTP access from network 200.200.10.0 to network 200.199.11.0 but allow everything else, which of the following command strings is valid?
Options- A. access-list 110 deny 200.200.10.0 to network 200.199.11.0 eq ftp
access-list 111 permit ip any 0.0.0.0 255.255.255.255 - B. access-list 1 deny ftp 200.200.10.0 200.199.11.0 any any
- C. access-list 100 deny tcp 200.200.10.0 0.0.0.255 200.199.11.0 0.0.0.255 eq ftp
- D. access-list 198 deny tcp 200.200.10.0 0.0.0.255 200.199.11.0 0.0.0.255 eq ftp
access-list 198 permit ip any 0.0.0.0 255.255.255.255
Discuss
Correct Answer: access-list 198 deny tcp 200.200.10.0 0.0.0.255 200.199.11.0 0.0.0.255 eq ftp
access-list 198 permit ip any 0.0.0.0 255.255.255.255
Explanation:
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.
- 2. Which router command allows you to view the entire contents of all access lists?
Options- A. Router# show interface
- B. Router> show ip interface
- C. Router# show access-lists
- D. Router> show all access-lists Discuss
Correct Answer: Router# show access-lists
Explanation:
The
show access-lists command will allow you to view the entire contents of all access lists, but it will not show you the interfaces to which the access lists are applied.
- 3. Which of the following is true regarding access lists applied to an interface?
Options- A. You can place as many access lists as you want on any interface until you run out of memory.
- B. You can apply only one access list on any interface.
- C. One access list may be configured, per direction, for each layer 3 protocol configured on an interface.
- D. You can apply two access lists to any interface. Discuss
Correct Answer: One access list may be configured, per direction, for each layer 3 protocol configured on an interface.
Explanation:
A Cisco router has rules regarding the placement of access lists on a router interface. You can place one access list per direction for each layer 3 protocol configured on an interface.
- 4. Which command would you use to apply an access list to a router interface?
Options- A. ip access-list 101 out
- B. access-list ip 101 in
- C. ip access-group 101 in
- D. access-group ip 101 in Discuss
Correct Answer: ip access-group 101 in
Explanation:
To apply an access list, the proper command is
ip access-group 101 in.
- 5. Which of the following is an example of a standard IP access list?
Options- A. access-list 110 permit host 1.1.1.1
- B. access-list 1 deny 172.16.10.1 0.0.0.0
- C. access-list 1 permit 172.16.10.1 255.255.0.0
- D. access-list standard 1.1.1.1 Discuss
Correct Answer: access-list 1 deny 172.16.10.1 0.0.0.0
Explanation:
Standard IP access lists use the numbers 1-99 and 1300-1999 and filter based on source IP address only. Option C is incorrect because the mask must be in wildcard format.
- 6. What command will permit SMTP mail to only host 1.1.1.1?
Options- A. access-list 10 permit smtp host 1.1.1.1
- B. access-list 110 permit ip smtp host 1.1.1.1
- C. access-list 10 permit tcp any host 1.1.1.1 eq smtp
- D. access-list 110 permit tcp any host 1.1.1.1 eq smtp Discuss
Correct Answer: access-list 110 permit tcp any host 1.1.1.1 eq smtp
Explanation:
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.
- 7. You configure the following access list:
What will the result of this access list be?access-list 110 deny tcp 10.1.1.128 0.0.0.63 any eq smtp access-list 110 deny tcp any eq 23 int ethernet 0 ip access-group 110 out
Options- A. Email and Telnet will be allowed out E0.
- B. Email and Telnet will be allowed in E0.
- C. Everything but email and Telnet will be allowed out E0.
- D. No IP traffic will be allowed out E0. Discuss
Correct Answer: No IP traffic will be allowed out E0.
Explanation:
If you add an access list to an interface and you do not have at least one
permit statement, then you will effectively shut down the interface because of the implicit
deny any at the end of every list.
- 8. If you wanted to deny all Telnet connections to only network 192.168.10.0, which command could you use?
Options- A. access-list 100 deny tcp 192.168.10.0 255.255.255.0 eq telnet
- B. access-list 100 deny tcp 192.168.10.0 0.255.255.255 eq telnet
- C. access-list 100 deny tcp any 192.168.10.0 0.0.0.255 eq 23
- D. access-list 100 deny 192.168.10.0 0.0.0.255 any eq 23 Discuss
Correct Answer: access-list 100 deny tcp any 192.168.10.0 0.0.0.255 eq 23
Explanation:
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.
- 9. You have created a named access list called Blocksales. Which of the following is a valid command for applying this to packets trying to enter interface s0 of your router?
Options- A. (config)# ip access-group 110 in
- B. (config-if)# ip access-group 110 in
- C. (config-if)# ip access-group Blocksales in
- D. (config-if)# blocksales ip access-list in Discuss
Correct Answer: (config-if)# ip access-group Blocksales in
Explanation:
Using a named access list just replaces the number used when applying the list to the router's interface.
ip access-group Blocksales in is correct.
- 10. Which of the following access lists will allow only HTTP traffic into network 196.15.7.0?
Options- A. access-list 100 permit tcp any 196.15.7.0 0.0.0.255 eq www
- B. access-list 10 deny tcp any 196.15.7.0 eq www
- C. access-list 100 permit 196.15.7.0 0.0.0.255 eq www
- D. access-list 110 permit ip any 196.15.7.0 0.0.0.255
- E. access-list 110 permit www 196.15.7.0 0.0.0.255 Discuss
Correct Answer: access-list 100 permit tcp any 196.15.7.0 0.0.0.255 eq www
Explanation:
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.
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