Instances Unable to Reach External Server for Updates
Question
Your VPC consists of public and private subnets.
The private subnets make use of NAT Gateway to download updates from the internet.
The Instances are trying to download updates from a server that listens on port 8090
But the instances are not able to reach the external server for updates.
Which of the following could be relevant issues with this? (Select THREE)
Answers
Explanations
Click on the arrows to vote for the correct answer
A. B. C. D.Answer - A, B, and D.
The NAT instance could be blocking Outbound Traffic on port 8090 which is not allowing traffic to flow outwards.
The remote server could also be blocking traffic from the instances.
Option B is CORRECT because NACL inbound rule must allow ephemeral ports for outbound traffic.
Option C is INCORRECT because the server already listens on port 8090 and since security groups are stateful, even the outbound would be allowed on port 8090.
Option D is CORRECT because the question is asking for "relevant issues" and therefore the firewall can also be considered here.
For more information on NAT Instances, please visit the below URL.
https://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_NAT_Instance.htmlThere are multiple factors that can cause the instances in the private subnets to not reach the external server for updates on port 8090. Here are the possible issues:
A. The NAT Gateway is blocking traffic on port 8090: The NAT Gateway is responsible for translating the private IP address of the instances to a public IP address when they communicate with the internet. By default, NAT Gateway allows all outbound traffic but blocks all inbound traffic. In this case, the issue could be that the NAT Gateway is not configured to allow traffic on port 8090. To resolve this, you need to add a rule in the NAT Gateway's security group to allow traffic on port 8090.
B. The Inbound NACL is blocking traffic on port 8090: Network ACLs (NACLs) are stateless firewalls that control inbound and outbound traffic at the subnet level. If the inbound NACL is blocking traffic on port 8090, then the instances in the private subnet won't be able to reach the external server on that port. To resolve this, you need to add a rule in the inbound NACL to allow traffic on port 8090.
C. The Inbound Security Groups are blocking traffic on port 8090: Security groups are stateful firewalls that control inbound and outbound traffic at the instance level. If the inbound security group is blocking traffic on port 8090, then the instances won't be able to reach the external server on that port. To resolve this, you need to add a rule in the inbound security group to allow traffic on port 8090.
D. The remote server firewall is blocking traffic: It's possible that the issue is not with your VPC but with the external server's firewall. If the external server firewall is blocking traffic on port 8090, then the instances won't be able to reach the server on that port. In this case, you need to check with the server owner to see if they can allow traffic on port 8090 from your VPC's IP address range.
In summary, the three possible issues that could be preventing the instances in the private subnets from reaching the external server on port 8090 are:
- The NAT Gateway is not allowing traffic on port 8090.
- The inbound NACL is blocking traffic on port 8090.
- The inbound security group is blocking traffic on port 8090.
You should check each of these configurations and rules to ensure that they are allowing traffic on port 8090.
