![]() You can find this via the SG console or web services like "what is my IP address." For instance, even though it is 'just a lab' practice limiting inbound traffic to just your personal workstation (or your external firewall) and just the ports you need. So it is incumbent on you to take all reasonable precautions, even in a lab. (Even a lab machine can be useful as an attack bot). There are many smart, motivated, and well funded people who will try to compromise your system. Plus, optional network IDPS systems to monitor for odd behaviour on the networks.Our hosting provider's perimeter Network firewalls.We use per-device fire walls functionality such as Security Groups and nACLs.We maintain our anti-virus / anti-malware tooling to block attacks from the inside.They have tests to confirm that it is response traffic and has the correct hand shaking. We maintain a healthy un-compromised Network stack that will not accept new inbound conversations on the ephemeral ports (unless you tell them to).However that is a reason that we use the provided tooling, do patching, and hosting providers deploy all those expensive network protection services for us. Those who are malicious can easily craft a script to work directly on the NIC to direct traffic to the ephemeral ports on your instance. This is quite robust assuming two things:ġ/ You do your patching so that the operating system is kept up to date with any discovered weaknesses.Ģ/ You don't allow a virus or trojan into your system though some other means which could then issue the right instructions to open these ports from the inside. The Operating System network stack enforces rules that prevent new conversations being started on these ports unless explicitly authorised by a higher level application. There are intended to only be used in an 'established' communication stream. These tools and methods are part of application design and the tools that a developer chooses to use in the application. This may mean that embedded scripts or commands or binary objects are blocked or stripped out preventing bad players from using them to try and bypass the application security. ![]() We can use application code (layer 7) to filter what can come in to the application. New conversations may need to go through an application (layer 7) authentication process. ![]() For instance session state will allow us to seperate conversations that we are already having with authenticated people, from unauthenticated people trying to start a new conversation. However we use the other layers to filter them out, layers 5 through 7. As noted before we have to let some traffic in to provide service to our customers, so what is to stop a bad player from coming in the same ports and attacking you. This is where the Security Groups and network Access Control Lists (nACLs) work. In the lower layers we can exclude traffic from certain addresses and using certain protocols. While originally intended to describe communication protocols, it is also useful to describe the layers of filtering that can be used in security. In networking there is the concept of the OSI stack which describes the network as a series of layers that ranging form the purely binary signals up to complex applications. Security is implemented by having multiple tools and methods that narrows the traffic to just what is needed, and then again filters the the content of the traffic. You cannot service Customers without opening these ports, so how do we exclude hackers? The only difference between a customer and a hacker is intent. Would a NAK only protocol be preferable to a protocol that uses ACK's? Why? Now, suppose the sender has a lot of data to send and the end-to-end connection experiences a few losses.Is opening Ephemeral ports safe ? Are we not opening our network to the hackers? Suppose sender sends data only infrequently. Which calls should be blocking (that is, not returning until some external stimulus is received)? Consider a reliable data transfer protocol that uses only negative acknowledgements. Assume all the method/function calls needed are already defined. What does the following snippet of code do? (InetAddress.getLocalHost().getHostAddress()) Write a pseudocode algorithm that describes the receiver side of RDT 3.0. Show code to create an output stream to a Java Socket. Show code to create an input stream to a Java Socket. Briefly list the differences between TCP and UDP. What is an ephemeral port? What port number range is typically defined for these ports? b.
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