Tag: NAT overload

In this lab, we will run through the process of setting up a small network. We will use this network to show the different types of ACLs. We will start by using a standard named ACL in order to allow traffic to use NAT (PAT) to permit our workstation LAN network to access the internet. We will then create an extended network to permit web traffic but block others.

Change hostname Rtr-1
Access the router and change the hostname to ‘Rtr-1’. Configure the router to use Google’s DNS IP ‘8.8.8.8’.

Router>enable
Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#hostname Rtr-1
Rtr-1(config)#ip domain-lookup
Rtr-1(config)#ip name-server 8.8.8.8

Configure Rtr-1 Interfaces
Configure each interface of Rtr-1 as they appear in the table above.

Rtr-1(config)#interface Gi0/0
Rtr-1(config-if)#ip address dhcp
Rtr-1(config-if)#no shutdown
Rtr-1(config-if)#exit
Rtr-1(config)#interface Gi0/1
Rtr-1(config-if)#ip address 192.168.5.1 255.255.255.0
Rtr-1(config-if)#no shutdown
Rtr-1(config-if)#exit
Rtr-1(config)#interface Gi0/2
Rtr-1(config-if)#ip address 10.200.1.1 255.255.255.240
Rtr-1(config-if)#no shutdown
Rtr-1(config-if)#exit
Rtr-1(config)#

Create a DHCP server on Router 1 name it Workstation-LAN
Setup a DHCP Pool named Workstation-LAN. Set the network as 192.168.5.0/24. Configure the DNS server to use Google’s DNS server IP address ‘8.8.8.8’. Set the gateway as the IP assigned to interface Gi 0/1. Reserve the first 25 IPs and the last 55 IPs.

Rtr-1(config)#ip dhcp pool Workstation-LAN
Rtr-1(dhcp-config)#network 192.168.5.0 255.255.255.0
Rtr-1(dhcp-config)#network 192.168.5.0 255.255.255.0
Rtr-1(dhcp-config)#default-router 192.168.5.1
Rtr-1(dhcp-config)#dns-server 8.8.8.8
Rtr-1(dhcp-config)#exit
Rtr-1(config)#ip dhcp excluded-address 192.168.5.1 192.168.5.25
Rtr-1(config)#ip dhcp excluded-address 192.168.5.201 192.168.5.255

Set up PC-1 to a Dynamic IP address
I am using a Docker container in this lab, but you can use a Linux VM, Windows VM, or even a Virtual PC. If you are using the Docker container in EVE-NG make sure to Enable DHCP on Eth 0 is checked in the configuration window.

Set up Web-Svr as a Static IP
Configure the Web Server to use a static IP as it appears in the table above. Using a terminal configure the IP address. In this lab, I used a Docker container you can use a Linux VM, Windows VM, or a Virtual PC.

root@Web-Svr:~# ip addr add 10.200.1.4/28 dev eth0
root@Web-Svr:~# ip route add default via 10.200.1.1

Configure NAT Overload (PAT) on Rtr-1
Define the inside and outside interfaces on Rtr-1. Create a standard named ACL, using the name ‘NAT-ACL’. Permit the Workstation-LAN on the ACL. Set the ACL ‘NAT-ACL’ as the inside source and set the outside interface to overload.

Rtr-1(config)#interface Gi0/0
Rtr-1(config-if)#ip nat outside
Rtr-1(config-if)#exit
Rtr-1(config)#interface Gi0/1
Rtr-1(config-if)#ip nat inside
Rtr-1(config-if)#exit
Rtr-1(config)#ip access-list standard NAT-ACL
Rtr-1(config-std-nacl)#permit 192.168.5.0 0.0.0.255
Rtr-1(config-std-nacl)#exit
Rtr-1(config)#ip nat inside source list NAT-ACL interface Gi0/0 overload

Verify PC-1 can access internet websites
Open an RDP session to PC-1 and open a web browser and connect to any website to verify connectivity.

Start a simple web server
If you are using Docker Container in Eve-NG Pro ‘Gui-Server’ as I did you will not need to follow these instructions. If you are using a Linux VM add the following commands in the Linux terminal.

sudo apt update
sudo apt install apache2

After entering those commands you should be able to open the PC-1 web browser and access the apache webserver by typing the Web-Svr IP in the search bar of the browser like so ‘http://10.200.1.4’.

Start a Python SimpleHTTP Server on port 8080
Return back to the Web-Svr terminal and enter the following command in order to start an additional webserver on the Web-Svr.

root@Web-Svr:~# python -m SimpleHTTPServer 8080
Serving HTTP on 0.0.0.0 port 8080 ...

After entering those commands you should be able to open the PC-1 web browser and access the SimpleHTTPServer app using port 8080 and the IP address of the Web-Svr.

Create an extended ACL to block PC-1 access to port 80 but continue to permit 8080
Access Rtr-1 and configure an extended ACL using the access-list number 104. Assign the ACL to the appropriate interface. Remember the ACL created should be configured closer to the source.

Rtr-1(config)#ip access-list extended 104
Rtr-1(config-ext-nacl)#permit tcp host 192.168.5.26 host 10.200.1.4 eq 8080
Rtr-1(config-ext-nacl)#deny tcp host 192.168.5.26 host 10.200.1.4 eq 80
Rtr-1(config-ext-nacl)#exit
Rtr-1(config)#interface Gi0/1
Rtr-1(config-if)#ip access-group 104 in

Verify that PC-1 no longer has access to Port 80 of the Web-Svr

Verify the PC-1 still has access to port 8080 of the Web-Svr

Uh oh PC-1 No longer has access to the internet.

Fix the ACL so that PC-1 regains Internet Access
Change the ACL to permit all other traffic before the implicit deny.

Rtr-1(config)#ip access-list extended 104
Rtr-1(config-ext-nacl)#permit ip any any
Rtr-1(config-ext-nacl)#end

Verify that PC-1 can now access the internet after the ACL changes

You have completed the lab.