Shorewall configuration tool

After that, the accept prompt opens up. This asks permission for a couple of dependencies to install along with Shorewall.

Here we edit the configuration according to our requirements. After configuration, we save the file. The Shorewall has an inbuilt check tool for checking the configuration by applying the following command. While checking, If we could not trace any problem in configuration file then we can clear the Shorewall.

Recently, one of the customers approached us to restrict SSH access to the server. He wanted to access the server only from one of the IP addresses. Before editing, we required the name of the interface used by the customer. So we ran the following command. Initially, we created the zone file and call it loc for local traffic.

For providing a secure shell from For port forwarding, we added the DNAT entry. After all editing in the configuration files, we have then checked the Shorewall and restarted. In short, Shorewall is an open-source firewalling tool for making the task of network security easier.

It also helps easier handling of zones. So any address a. A Shorewall user has contributed a useful graphical summary of the above information. Later in this guide, you will see the notation a. This simply means that the interface is configured with ip address a.

One of the purposes of subnetting is that it forms the basis for routing. Here's the routing table on my firewall compressed for PDF :. The first three routes are host routes since they indicate how to get to a single host. The last route is the default route and the gateway mentioned in that route is called the default gateway. When the kernel is trying to send a packet to IP address A , it starts at the top of the routing table and:.

Lets take an example. Suppose that we want to route a packet to That address clearly doesn't match any of the host routes in the table but if we logically and that address with One more thing needs to be emphasized -- all outgoing packet are sent using the routing table and reply packets are not a special case. There seems to be a common misconception whereby people think that request packets are like salmon and contain a genetic code that is magically transferred to reply packets so that the replies follow the reverse route taken by the request.

That isn't the case; the replies may take a totally different route back to the client than was taken by the requests -- they are totally independent. When sending packets over Ethernet, IP addresses aren't used. As you can see from the above output, the MAC is 6 bytes 48 bits wide.

A card's MAC is usually also printed on a label attached to the card itself. Here is ARP in action:. In this exchange, Notice that the last entry in the table records the information we saw using tcpdump above. These RIRs may in turn delegate to national registries. It's a fact of life that most of us can't afford as many Public IP addresses as we have devices to assign them to so we end up making use of Private IP addresses. RFC reserves several IP address ranges for this purpose:.

The addresses reserved by RFC are sometimes referred to as non-routable because the Internet backbone routers don't forward packets which have an RFC destination address.

This is understandable given that anyone can select any of these addresses for their private use but the term non-routable is somewhat unfortunate because it leads people to the erroneous conclusion that traffic destined for one of these addresses can't be sent through a router. This is definitely not true; private routers including your Shorewall-based firewall can forward RFC addressed traffic just fine.

As the IPv4 address space becomes depleted, more and more organizations including ISPs are beginning to use RFC addresses in their infrastructure. You don't want to use addresses that are being used by your ISP or by another organization with whom you want to establish a VPN relationship. So it's a good idea to check with your ISP to see if they are using or are planning to use private addresses before you decide the addresses that you are going to use.

These "real" addresses are not to be confused with addresses in The choice of how to set up your network depends primarily on how many Public IP addresses you have vs. Regardless of how many addresses you have, your ISP will handle that set of addresses in one of two ways:.

Routed - Traffic to any of your addresses will be routed through a single gateway address. Non-routed - Your ISP will send traffic to each of your addresses directly. If you are using the Debian package, please check your shorewall. Let's assume that your ISP has assigned you the subnet That means that you have IP addresses Your ISP has also told you that you should use a netmask of Here, the DMZ comprises the subnet The default gateway for hosts in the DMZ would be configured to Notice that this arrangement is rather wasteful of public IP addresses since it is using What if DMZ 1 The routing table on DMZ 1 will look like this:.

Most of us don't have the luxury of having enough public IP addresses to set up our networks as shown in the preceding example even if the setup is routed. Clearly, that set of addresses doesn't comprise a subnetwork and there aren't enough addresses for all of the network interfaces.

There are four different techniques that can be used to work around this problem. Often a combination of these techniques is used. Each of these will be discussed in the sections that follow. When B responds and the response is received by the firewall, the firewall changes the destination address back to the RFC address of A and forwards the response back to A.

Let's suppose that you decide to use SNAT on your local zone and use public address When running Shorewall 5. This example used the normal technique of assigning the same public IP address for the firewall external interface and for SNAT. When SNAT is used, it is impossible for hosts on the Internet to initiate a connection to one of the internal systems since those systems do not have a public IP address.

DNAT provides a way to allow selected connections from the Internet. To review Shorewall functionality, see the Features Page. New to Shorewall? Download the current Stable version see above then select the Getting Started Guide that meets your need.

Once Shorewall has configured the Linux networking subsystem, its job is complete and there is no Shorewall process left running on your system. Website: shorewall. Shorewall is written in Perl. Learn Perl with our recommended free books and free tutorials. This site uses Akismet to reduce spam. Learn how your comment data is processed. Share this article. Share your Thoughts Cancel reply. New to Linux?