Network Element for Rectification

Correct Answer: B.

NACL is stateless.

Specific entries need to be added for both inbound and outbound traffic.

In the above case, since incoming traffic is seen as accepted in VPC flow logs, inbound rules are properly added in NACL.

Since outgoing traffic is getting rejected, NACL outbound rules need to be checked.

Option A is incorrect.

As logs show inbound requests from public IP addresses are allowed, a proper inbound security group is attached to the instance.

Since the Security group is stateful, it will be allowed outbound traffic for all inbound traffic.

Option C is incorrect.

Since all other Amazon EC2 instances can't ping, there is no issue with the VPC route table.

Option D is incorrect.

From the VPC flow logs, it is seen that Instance is assigned a private IP address, is not a public Elastic IP address.

For more information on VPC Flow Logs, refer to the following URL,

https://docs.aws.amazon.com/vpc/latest/userguide/flow-logs-records-examples.html

The IT team is trying to ping a new Amazon EC2 instance from a public network, but it is failing even though they have enabled internet access on the instance. In this situation, the team has captured VPC flow logs to troubleshoot the issue.

The flow logs indicate that the instance is receiving traffic from the public network, but the traffic is being rejected when it tries to reply. This means that the instance is receiving traffic but not responding, which could indicate a problem with the networking configuration.

To identify the root cause, the network elements involved in the traffic flow need to be checked. The flow logs show the source and destination IP addresses, as well as the action taken (ACCEPT or REJECT). The next step is to identify the network element that is blocking the traffic.

The flow logs show that the traffic is flowing through an Elastic Network Interface (ENI) with the ID "eni-1111b8ca111111111". This ENI is associated with the new EC2 instance that the team is trying to ping. Therefore, the problem is likely related to the configuration of the network elements associated with this ENI.

The VPC flow logs also indicate that the traffic is being rejected when it tries to leave the ENI. This means that the problem could be related to the configuration of the security group or network access control list (NACL) associated with the ENI.

Security groups are stateful firewalls that control inbound and outbound traffic to an EC2 instance. They are associated with the ENI and specify the rules for allowing or denying traffic based on the protocol, port, and source/destination IP addresses.

NACLs are stateless firewalls that control inbound and outbound traffic at the subnet level. They are associated with the VPC subnet and specify the rules for allowing or denying traffic based on the protocol, port, and source/destination IP addresses.

Based on the flow logs, it is clear that the traffic is being rejected when it tries to leave the ENI, which means that the security group or NACL associated with the ENI is blocking the traffic. Therefore, options A and B (Security Group and NACL) are the network elements that need to be checked for rectification.

Option C (VPC Route table) is unlikely to be the cause of the problem since the flow logs show that the traffic is reaching the ENI. The route table is used to determine the path that traffic takes to reach its destination, but it does not control the traffic flow at the ENI level.

Option D (Elastic IP address) is also unlikely to be the cause of the problem since the flow logs do not indicate any issues with the IP address. Elastic IP addresses are used to provide a fixed, public IP address to an EC2 instance, but they do not control the traffic flow at the ENI level.

In summary, the network element that needs to be checked for rectification in this scenario is either the Security Group or NACL associated with the ENI.