How to handle ephemeral ports in Security Groups and Network ACLsĪWS Confused about ephemeral ports? We have the expertise to help you tighten your network security in AWS. Option E: A security group with rules that allow outgoing traffic on port 443 and incoming traffic on ephemeral portsAbout Allies Contact 01508 494488 Share on Twitter Share on LinkedIn Share on Facebook Knowledge Base Additionally, inbound traffic should not be allowed unless there is a specific reason to do so. This option allows inbound traffic on port 443, which is not necessary for outbound traffic to an external web service. Option C: A Network ACL with a rule that allows outbound traffic on port 443 and inbound traffic in port 443 However, this option is not necessary for HTTPS traffic, as HTTPS traffic only uses port 443. This option allows inbound traffic in ephemeral ports, which are randomly assigned ports used by the instances to communicate with the external web service. Option B: A Network ACL with a rule that allows outbound traffic on port 443 and inbound traffic in ephemeral ports Therefore, to further minimize exposure, both options A and D should be implemented together. However, this option does not address inbound traffic, which means that any traffic from the external web service will be allowed into the instance. By default, all outbound traffic is denied, so a security group rule must be created to allow traffic on port 443. This option allows outbound traffic on port 443 from the instances, which is required to call the external web service. Option D: A Security Group with a rule that allows outbound traffic on port 443 However, this option does not address inbound traffic, which means that any traffic from the external web service will be allowed into the subnet. By default, all outbound traffic is allowed, but if there are any deny rules, they must be removed or modified to allow traffic on port 443. This option allows outbound traffic on port 443, which is required for the EC2 instances to call the external web service. Option A: A Network ACL with a rule that allows outbound traffic on port 443 They control traffic based on the security group rules, which are essentially allow rules. Security Groups, on the other hand, are stateful and operate at the instance level. They control traffic coming in and out of the subnet based on the source and destination IP addresses, protocols, and ports. Network ACLs are stateless and operate at the subnet level. A VPC has subnets, each with its own Network Access Control List (ACL) and Security Group. Option A: A Network ACL with a rule that allows outbound traffic on port 443 Option D: A Security Group with a rule that allows outbound traffic on port 443Ī Virtual Private Cloud (VPC) is a virtual network that provides a secure and isolated environment for running AWS resources. To minimize the exposure of EC2 instances in a public subnet calling an external web service via HTTPS (port 443), the following two options are recommended: Option E is invalid since you are allowing additional ports on Security groups that are not required.įor more information on VPC Security Groups, please visit the below URL: Option C is invalid because it needs to ensure incoming traffic on ephemeral ports and not only port 443. You also need to ensure incoming traffic on ephemeral ports. Option A is invalid because this rule alone is not enough. The Incoming traffic should be allowed on ephemeral ports for the Operating System on the Instance to allow a connection to be established on any desired or available port. Since the traffic needs to flow outbound from the Instance to a web service on Port 443, the outbound rules on both the Network and Security Groups need to allow outbound traffic. Click on the arrows to vote for the correct answer A.
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