The better option for control in almost all scenarios is to use security groups as your main control point as it is statefull and controls traffic at a the elastic networking interface. Not to mention the fact that NACL's only control traffic at a subnet level so traffic between instances inside the same subnet wont ever be evaluated by the NACL. NACL's should be used for broad stroke control like allowing access to the IP addresses of your internal production network to the AWS prod but denying any access from the user or Dev IP space. This lack of tracking and requirement to open so many ports when using NACL's is the reason we dont recommend using them for fine grain access control. ![]() So that being said when using a stateless firewall, like the NCAL's, since the firewall doesn't track sessions you have to open the dynamic port range to allow for proper communication. the service on port 80/443 is the first person who hands you a ticket and the windows is the higher level port used to completed the session. That ticket tells you what window to go to in order to complete the task you are there for. After you respond they give you a ticket with a number on it. Think of it like you walk into a DMV (or other government building that handles multiple functions) the first person you see asks you what you are here for. The server does this because multiple people can't communicate on a single port so to handle more than one client it moves known traffic to the dynamic port ranges. The webserver captures the request and then sends you a response that tells your computer what port it needs to use for this communication session. Take web traffic for example, when you request a webpage your computer sends a request to web servers on port 80 or 443. Now the trouble with this is that most Protocols do not stick to a single Port number. NACL is a stateless firewall meaning that you have to define all the required ports both inbound and outbound. Later Windows versions, including Vista, Windows 7 and Server 2008, use the Internet Assigned Number Authority (IANA) suggested range of 49152-65535.So the problem is your customer is looking at NACL's and thinking they are traditional firewall rules and they are not. ![]() Many Linux versions use port range 32768-61000, while Windows versions (until XP) use 1025-5000, by default. ![]() However, it is usually reused only after the entire port range is used up.ĭifferent operating systems (OS) use different port ranges for ephemeral ports. Instead, the server to the client uses a new, temporarily assigned port that the client provides as the source port.Īfter communication is terminated, the port becomes available for use in another session. However, because the server does not initialize communication, it should not use a well-known port to send replies to the client, just in case a server-type application is running on that client device. In client-server processes that use Transmission Control Protocol/Internet Protocol (TCP/IP) or User Datagram Protocol (UDP), the client initiates communication with a server through one of the many well-known ports. Ephemeral means temporary or short-lived, as is the characteristic of this type of port.
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