The Managed Server Computers can now initiate connections to the external network and surf the Internet, which is not intended or required. The outbound rule is not required at all and actually opens up undesired access. The Inbound rule is correct as it allows for the client to initiate the two way conversation. It is a reasonable mistake to assume you need a rule to allow the traffic back to the client. This is because there is an existing socket that can be, and is used. There is no need for a second outbound rule to allow the web server to talk back to the client. This would allow the client to initiate the conversation and receive the data back. To use a very simple example, let's look at the firewall rule required to allow a Source or Client machine to request a website from a web-server or destination: This socket is now a two way pathway or channel through which traffic moves between client and server. During the lifespan of the socket, the port number on the source and destination will not change.
At this point you have a TCP socket or conversation pair. The client machine receives the SYN-ACK packet from the destination and sends back a final ACK packet.The destination machine sends back a SYN-ACK packet. The destination or server is the computer receiving the SYN conversation request on the specified static service port.A port is dynamically allocated on the source machine and the request is sent to the destination on the predefined static service port. The source or client is the computer initiating the conversation with a SYN packet.At its most basic, a firewall rule consists of 5 objects:įor a TCP rule such as HTTP, the following three step handshake applies: The very essence of a firewall is to limit or restrict unwanted traffic, it does this by evaluating specific criteria. Let me explain why this rule is bad and some of it unnecessary. The thinking being that the client needs a way to connect to the web server and that the web server needs a way to connect back to the client. The result is a rule that looks like this. They way traffic is evaluated and processed by a firewall is not always understood correctly. I can speculate on a number of reasons how these rules actually get defined and implemented, but it all comes down to the same thing.
The one I see most often is potentially the worst. When I look at firewalls rule sets maintained by other companies, I often notice the same common mistakes.
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