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CCNA Access List Sim 2

February 15th, 2014 Go to comments

Question

access_list_sim2.jpg

Answer and Explanation

(Note: If you are not sure how to use access-list, please check out my access-list tutorial at: http://www.9tut.com/access-list-tutorial, also some modifications about the access-list have been reported so you should read the “Some modifications” section at the end of this question to understand more. You can also download this sim to practice (open with Packet Tracer) here: http://www.9tut.com/download/9tut.com_Access-list_sim2.pkt

Corp1>enable (you may enter “cisco” as it passwords here)

We should create an access-list and apply it to the interface which is connected to the Server LAN because it can filter out traffic from both Sw-2 and Core networks. The Server LAN network has been assigned addresses of 172.22.242.17 – 172.22.242.30 so we can guess the interface connected to them has an IP address of 172.22.242.30 (.30 is the number shown in the figure). Use the “show running-config” command to check which interface has the IP address of 172.22.242.30.

Corp1#show running-config

access_list_sim_show_running.jpg

We learn that interface FastEthernet0/1 is the interface connected to Server LAN network. It is the interface we will apply our access-list (for outbound direction).

Corp1#configure terminal

Our access-list needs to allow host C – 192.168.33.3 to the Finance Web Server 172.22.242.23 via web (port 80)

Corp1(config)#access-list 100 permit tcp host 192.168.33.3 host 172.22.242.23 eq 80

Deny other hosts access to the Finance Web Server via web

Corp1(config)#access-list 100 deny tcp any host 172.22.242.23 eq 80

All other traffic is permitted

Corp1(config)#access-list 100 permit ip any any

Apply this access-list to Fa0/1 interface (outbound direction)

Corp1(config)#interface fa0/1
Corp1(config-if)#ip access-group 100 out

Notice: We have to apply the access-list to Fa0/1 interface (not Fa0/0 interface) so that the access-list can filter traffic coming from both the LAN and the Core networks. If we apply access list to the inbound interface we can only filter traffic from the LAN network.

In the exam, just click on host C to open its web browser. In the address box type http://172.22.242.23 to check if you are allowed to access Finance Web Server via HTTP or not. If your configuration is correct then you can access it.

Click on other hosts (A, B and D) and check to make sure you can’t access Finance Web Server from these hosts.

Finally, save the configuration

Corp1(config-if)#end
Corp1#copy running-config startup-config

(This configuration only prevents hosts from accessing Finance Web Server via web but if this server supports other traffic – like FTP, SMTP… then other hosts can access it, too.)

Notice: You might be asked to allow other host (A, B or D) to access the Finance Web Server so please read the requirement carefully.

Some modifications (mods):

Modification 1 (Mod 1):

permit host B from accessing finance server access-list 100 permit ip host 192.168.33.2 host 172.22.242.23
deny host B from accessing other servers (not the whole network) access-list 100 deny ip host 192.168.33.2 172.22.242.16 0.0.0.15
permit everything else access-list 100 permit ip any any

Modification 2 (Mod 2):

Only allow Host C to to access the financial server access-list 100 permit ip host 192.168.33.3 host 172.22.242.23
Not allow anyone else in any way communicate with the financial server access-list 100 deny ip any host 172.22.242.23
Allow all other traffic access-list 100 permit ip any any

Modification 3 (Mod 3):

– Host C should be able to use a web browser(HTTP)to access the Finance Web Server access-list 100 permit tcp host 192.168.33.3 host 172.22.242.23 eq 80
– Other types of access from host C to the Finance Web Server should be blocked
– All access from hosts in the Core or local LAN to the Finance Web Server should be blocked
access-list 100 deny ip any host 172.22.242.23
(because the requirement says we can not use more than 3 statements so we have to use “any” here for the hosts in the Core and hosts in local LAN)
– All hosts in the Core and local LAN should be able to access the Public Web Server * access-list 100 permit ip any host
(If the question asks this, surely it has to give you the IP of Public Web Server) but in the exam you should use “access-list 100 permit ip any any”

Modification 4 (Mod 4):

Host C should be able to use a web browser to access the financial web server access-list 100 permit tcp host 192.168.33.3 host 172.22.242.23 eq 80
Other types of access from host C to the finance web server should be blocked access-list 100 deny ip host 192.168.33.3 host 172.22.242.23
All hosts in the core and on the local LAN should be able to access the Public web server * access-list 100 permit ip any host
(The IP of Public Web Server will surely be given in this question) but in the exam you should use “access-list 100 permit ip any any”

* There are some reports about the command of “All hosts in the core and on the local LAN should be able to access the Public web server” saying that the correct command should be “access-list 100 permit ip any any”, not “access-list 100 permit ip any host (IP of Public Web Server)”. Although I believe the second command is better but maybe you should use the first command “access-list 100 permit ip any any” instead as some reports said they got 100% when using this command (even if the question gives you the IP address of Public Web Server). It is a bug in this sim.

(Note: Don’t forget to apply this access list to the suitable interface or you will lose points
interface fa0/1
ip access-group 100 out

And in the exam, they may slightly change the requirements, for example host A, host B instead of host C… so make sure you read the requirement carefully and use the access-list correctly)

I created this sim in Packet Tracer v5.2.1 so you can practice with it. You will need new version of Packet Tracer to open it (v5.1+).

accesslist_sim2_packet_tracer.jpg

Download this sim here

Notice: After typing the commands above, if you make a “ping” from other hosts (PC0, PC1, PC3) then PC4 (Finance Web Server) can still reply because we just filter HTTP traffic, not ICMP traffic. To generate HTTP traffic, select “Web Browser” in the “Desktop” tab of these PCs. When a web browser opens, type the IP address of Finance Web Server and you can see how traffic flows in Simulation Mode.

accesslist2_test_http.jpg

And notice that in the initial configuration of this sim the Core network can ping Finance Web Server. We have to create an access-list that can filter this traffic too.

Comments
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    August 16th, 2017

    @ anony

    in the third statement you should use
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    What is the qustion in this lab? I see only the answer

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  9. Abdullah
    September 1st, 2017

    today 31-8-2017 this lab was one of the exam labs. one change as Modification 3 (Mod 3). I made all the requirement. at the end I issued copy running-config startup-config, the command is accepted an ” configuration build ok ” message is appeared but, when I check the startup config by show command I couldn’t find the configuration. all the configuration still in running config but not copyed. I tried many times but the same thing. I lost the points.

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  36. Jessy
    October 1st, 2017

    ACL MOD 1 and 4 can be applied to the interface closest do the source of the traffic?
    Because the text don’t say anything about the Core traffic. Especialy because we should apply extended ACL’s close to the source of the traffic, right?
    Now, ACL MOD 2 and 3 force us to apply to the interface closest to the destination.

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  41. GD
    October 17th, 2017

    Wouldn’t you apply the ACL on both the serial interface and the Fe0/0 inbound?

  42. alberhander
    October 20th, 2017

    Guys, I still have a doubt. The last line has to be “access-list 100 permit ip any any” always in the exam? Even if they give you the Public Server IP address?
    Please, someone clarify it. Thanks!

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