Showing posts with label firewall. Show all posts
Showing posts with label firewall. Show all posts

Saturday, June 2, 2012

Mapped IP configuration on Netscreen

         I'm going to talking about MIP feature on Nescreen via a sample network design. This network uses private addresses in the Internal Side and has got public addresses to use external side. The network structure is shown below,

         As shown on network design, we have a computer which has got ip address and we want to map it to public IP address. What we want is shown below:

         When computer sends any request to public Internet side, devices which are located on Internet side will see it as and when a request is sent from Internet to IP address, FW redirects it to IP address. So means and means

We will set MIP configuration on Netscreen for this purpose.

(The external side is defined as Internet zone and the internal network is defined as system zone on firewall before. Following configurations are illustrating as that zone names)

         First of all, is an IP address which is located in the segment between FW and Main router. This segment is not behind of a firewall, conversely, front of the firewall. The firewall should be taken on itself like a sub-interface. Anyway we have to see IP address in the main router ARP Table with a MAC address which is got from firewall. Otherwise, packages which contains in the destination field is not able to arrive to target. I will explain this background info at the end of this article. Let's continue to configuration.

         Select “Interfaces” item on the menu which is located on left side of the netscreen configuration web-interface.

         When Interfaces item is clicked, we can see a page as shown below on the right side of page.

         Clicking to Edit link which is marked on above picture. When It is clicked, following page will be opened.

         Clicking to MIP link, this page is listing already created MIPs.

         Clicking to New button on the right side.

         When clicking to OK and check MIP list again, we will see our configuration on the MIP list,

         Right now, Mapped IP configuration is done. But we have to create the policy to permit traffic. It should have both directions. The following one is about Internet to system direction.

         When you are clicking to policies under the policy menu, you can see policy list on the right side of the page. There are “from” and “to” commands at top of the right side. Select the “Internet” option from the combobox “from” and select system using the “to” part.  

         Right now, The firewall is listing policies from internet to system. Clicking to “New” buttom on the top-right side.

         These two points are important at this step. First, destination address should be MIP. Second, action should be “Permit”.

         Select “system” for 'from' part and select “Internet” for 'to' part on top side and click “go” button after than click to “New” button.

         Source address should be and destination address should be “any”. Than select permit for action.  

         This step permits access to Internet side for addressed computer. If you want to permit access from internet to your internal workstation only, you don't need this step.  

Let's analyse communication background on this scenario.

Telnet to Main router (It's Cisco 3661) and run “show arp” command. Getting output like below,

UGC_Topkapi_3661#show arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet          0   0010.dbff.22e0  ARPA   FastEthernet4/0
Internet        161   0010.dbff.22e0  ARPA   FastEthernet4/0

As you know, and ip addresses has got exactly same MAC address. The Main router should be send packages to firewall mac. The firewall know already how to access to main router. If you understand any step, let me know please.