Extended Access Control List is the Lab Scenario which has been repeatedly asked in the CCNA Routing & Switching Exam. Here I am going to show you the step by step configuration of the LAB.

A corporation wants to add security to its network. The requirements are:

  • Host B should be able to use a web browser (HTTP) to access the Finance Web Server.
  • Other types of access from host B 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.
  • All hosts in the Core and on local LAN should be able to access the Public Web Server.

You have been tasked to create and apply a numbered access list to a single outbound interface. This access list can contain no more than three statements that meet these requirements.

  • All passwords have been temporarily set to “cisco”.
  • The Core connection uses an IP address of 198.18.132.65.
  • The computers in the Hosts LAN have been assigned addresses of 192.168.201.1 – 192.168.201.254.
  • host A 192.168.201.1
  • host B 192.168.201.2
  • host C 192.168.201.3
  • host D 192.168.201.4
  • The Finance Web Server has been assigned an address of 172.22.237.17.
  • The Public Web Server in the Server LAN has been assigned an address of 172.22.237.18

Note: The IP Addresses will be different in the exam so make sure that you read the scenario properly.

Explanation:

We should create an access-list and apply it to the interface that is connected to the Server LAN because it can filter out traffic from both S2 and Core networks. To see which interface this is, use the “show ip interface brief” command:

From this, we know that the servers are located on the fa0/1 interface, so we will place our numbered access list here in the outbound direction.

Corp1#configure terminal

Our access-list needs to allow host B – 192.168125.2 to the Finance Web Server 172.22.109.17 via HTTP (port 80), so our first line is this:

Corp1(config)#access-list 100 permit tcp host 192.168.125.2 host 172.22.109.17 eq 80

Then, our next two instructions are these:

Other types of access from host B 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.

This can be accomplished with one command (which we need to do as our ACL needs to be no more than 3 lines long), blocking all other access to the finance web server:

Corp1(config)#access-list 100 deny ip any host 172.22.109.17

Our last instruction is to allow all hosts in the Core and on the local LAN access to the Public Web Server (172.22.109.18)

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

Finally, 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.

To verify, just click on host B to open its web browser. In the address box type http://172.22.109.17 to check if you are allowed to access Finance Web Server or not. If your configuration is correct then you can access it. Click on other hosts (A, C and D) and check to make sure you can’t access Finance Web Server from these hosts. Then, repeat to make sure they can reach the public server at 172.22.109.18. Finally, save the configuration

Corp1(config-if)#end

Corp1#copy running-config startup-config

Download the Packet Tracer file for this Lab: Click Here to Download

2 comments

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  • I believe there is something wrong with packet tracer as it does not allow the final command on the interface ip access-group 100 out
    it only provides the option for ip dhcp

    this could be a problem with my packet tracer only

    • I think there’s some problem with your packet tracer. You have to implement this command at the interface configuration mode.

      Eg:

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