Tutorial / Cram Notes
Virtual Private Cloud (VPC) Flow Logs is a feature that enables you to capture information about the IP traffic going to and from network interfaces in your VPC. As part of preparing for the AWS Certified Advanced Networking – Specialty (ANS-C01) examination, it’s crucial to understand both creating and analyzing VPC Flow Logs.
Creating VPC Flow Logs:
To create VPC Flow Logs, you can either use the Amazon VPC console or the AWS Command Line Interface (CLI). A Flow Log can be created for a VPC, a subnet, or a specific network interface.
Using Amazon VPC Console
- Sign into the AWS Management Console, and open the Amazon VPC console.
- In the navigation pane, choose ‘Your VPCs’, ‘Subnets’, or ‘Network Interfaces’ depending on the level at which you want to create the flow log.
- Select the resource and choose ‘Actions’, then ‘Create flow log’.
- In the Create Flow Log dialog, specify the details:
- The role with permissions that allows the flow logs to be published to CloudWatch Logs.
- The destination, which could be either CloudWatch Logs or Amazon S3.
- The traffic type to log, such as ‘All’, ‘Accepted’, or ‘Rejected’.
- Finally, create the flow log.
Using AWS CLI
aws ec2 create-flow-logs –resource-type VPC –resource-id vpc-<id> –traffic-type ALL –log-destination-type cloud-watch-logs –log-group-name <your-log-group> –deliver-logs-permission-arn <your-role-arn>
Analyzing VPC Flow Logs:
After creating flow logs, analyzing the captured data is critical for network troubleshooting, security analysis, and ensuring compliance with network policies.
Flow Log Record Fields
A flow log record includes the following fields:
Base Fields
- version: The VPC Flow Logs version number.
- account-id: The AWS account ID for the flow log.
- interface-id: The ID of the network interface for which the log records.
- srcaddr: The source IP address for the flow.
- dstaddr: The destination IP address for the flow.
- srcport: The source port of the traffic.
- dstport: The destination port of the traffic.
- protocol: The IANA protocol number of the traffic.
- packets: The number of packets transferred during the flow.
- bytes: The number of bytes transferred during the flow.
- start: The starting time of the flow.
- end: The ending time of the flow.
- action: The action (“ACCEPT” or “REJECT”) taken on the packet.
- log-status: The status of the flow log record (“OK” “NODATA” or “SKIPDATA”).
Extended Fields
- vpc-id: The ID of the VPC containing the network interface for which the flow log entry applies.
- subnet-id: The ID of the subnet containing the network interface for which the flow log entry applies.
- instance-id: The ID of the instance containing the network interface for which the flow log entry applies.
- tcp-flags: The bitmask value for TCP flags observed in the flow.
- type: The type of traffic: IPv4 or IPv6.
- pkt-srcaddr: The original source IP address of the traffic (before network address translation).
- pkt-dstaddr: The original destination IP address of the traffic (before network address translation).
Analyzing with CloudWatch Logs
When you set up flow logs to publish to CloudWatch Logs, you can use CloudWatch features to search and filter the traffic data. Here is how you can analyze the logs:
- Go to the CloudWatch Logs Console and select the log group you specified for your VPC Flow Logs.
- You can now filter the logs using CloudWatch syntax (e.g.,
{ dstaddr = "192.0.2.1" }to find records with that destination IP). - For a graphical representation or to perform metric filters to trigger alarms, you can use CloudWatch Insights or create CloudWatch Metrics based on your log data.
Analyzing with Amazon Athena
For large datasets or to perform complex queries, you might want to use Amazon Athena to analyze Flow Logs stored in Amazon S3.
- Set up Athena to query logs directly from the S3 bucket.
- Use SQL queries to explore and analyze the flow log data.
Example Athena Query
SELECT *
FROM vpc_flow_logs
WHERE action = ‘REJECT’
AND interface-id = ‘eni-xxxxxxxxxxxxxxxxx’
Understanding and correctly setting up VPC Flow Logs is vital to managing network traffic securely and efficiently. Configuring both the base and extended fields enables a comprehensive view of interaction within your VPC, and analyzing these logs allows you to draw valuable insights to secure and optimize your AWS environment for the AWS Certified Advanced Networking – Specialty exam.
Practice Test with Explanation
True or False: VPC flow logs can capture information about the IP traffic going to and from network interfaces in your VPC.
- True
True
VPC flow logs capture information about IP traffic going to and from network interfaces in your VPC, which is useful for security and network troubleshooting.
VPC Flow Logs can be created for which of the following AWS resources?
- A) Network Interfaces
- B) Subnets
- C) VPCs
- D) EC2 Instances
- E) Security Groups
A, B, C
VPC flow logs can be created for a specific network interface, a subnet, or an entire VPC but not directly for EC2 instances or security groups.
Which of the following fields are included in the base fields of VPC flow logs?
- A) srcaddr
- B) dstaddr
- C) traffic-path
- D) start
A, B, D
In the base fields of VPC flow logs, srcaddr (source IP address), dstaddr (destination IP address), and start (the time the flow started) are included. “traffic-path” is not a base field.
True or False: VPC flow logs can be delivered to both Amazon CloudWatch Logs and Amazon S
- True
True
VPC flow logs can be delivered to Amazon CloudWatch Logs for real-time analysis or to Amazon S3 for long-term storage.
What is the default storage duration for VPC Flow Logs in Amazon CloudWatch Logs?
- A) 24 hours
- B) Indefinitely, until manually deleted
- C) 90 days
- D) 365 days
B
By default, the flow log data is stored in the CloudWatch Logs log group indefinitely, until you manually delete the log data.
Which traffic is not logged by default in VPC Flow Logs?
- A) Traffic accepted by Security Groups
- B) DHCP traffic
- C) Traffic to and from the Amazon DNS server
- D) Amazon Windows license activation traffic
B, C, D
VPC Flow Logs do not capture DHCP traffic, traffic to the Amazon DNS server, and Amazon Windows license activation traffic by default.
True or False: You can filter VPC flow log records by the instance ID of the EC2 instance.
- False
False
VPC flow logs capture traffic based on network interfaces, so you cannot filter directly by instance ID. However, you can indirectly deduce the instance from the network interface ID if you know the relationship.
Which feature enables the capturing of additional metadata fields such as the VPC ID and Subnet ID in VPC Flow Logs?
- A) Custom Logging
- B) Extended Logging
- C) Enhanced Flow Logs
- D) Metadata fields
B
Extended Logging enables the capturing of additional metadata fields such as VPC ID and Subnet ID in VPC Flow Logs.
True or False: You can create VPC flow logs for VPCs that are peered with another AWS account.
- True
True
You can create VPC flow logs for VPCs that are peered with another AWS account, provided you have the necessary permissions to create flow logs.
Which IAM role permission is required to publish VPC flow logs to CloudWatch Logs?
- A) AmazonVPCFullAccess
- B) AmazonVPCReadOnlyAccess
- C) AmazonVPCFlowLogsRole
- D) CloudWatchLogsFullAccess
C
The IAM role specified must have the permissions that allow it to publish flow logs to CloudWatch Logs. Typically, the role has the policy trust relationship that allows the flow logs service to assume the role, often referred to as the AmazonVPCFlowLogsRole.
True or False: You can enable VPC Flow Logs after creating the VPC exclusively.
- False
False
VPC Flow Logs can be enabled at the time of VPC creation, for existing VPCs, and for specific subnets or network interfaces at any time.
What is the purpose of the ‘action’ field in extended VPC Flow Logs?
- A) Indicates whether the traffic was inbound or outbound
- B) Shows the AWS service to which the traffic was destined
- C) Identifies whether the traffic was allowed or denied by security groups or network ACLs
- D) Indicates the transport protocol
C
In extended VPC Flow Logs, the ‘action’ field identifies whether the traffic was allowed or denied based on the security groups or network ACLs associated with the network interface.
Interview Questions
What is a VPC flow log and why is it critical for network monitoring in AWS?
A VPC flow log is a feature that enables you to capture information about the IP traffic going to and from network interfaces in your VPC. It is critical for network monitoring as it helps in diagnosing security issues, understanding network patterns, and ensuring compliance with regulatory standards.
Can you describe the difference between the base and extended fields in VPC flow logs?
Base fields in a VPC flow log contain fundamental information about each network flow, such as source IP, destination IP, source port, destination port, protocol, and the allow or deny decision of the VPC security groups. Extended fields offer additional information like traffic flow direction (ingress or egress), the packet source (AWS or external), instance ID, TCP flags, and more. Extended fields provide a deeper level of insight into the flow log data.
What are the three levels of logging for VPC flow logs and what type of data is available at each level?
The three levels of logging for VPC flow logs are:
- Level 1 (VPC Flow Logs V1): The default level, capturing only the base fields.
- Level 2 (VPC Flow Logs V2): Captures additional metadata, such as VPC ID, subnet ID, and instance ID.
- Level 3 (VPC Flow Logs V3): Captures extended fields which include everything in Level 2 plus additional information like flow direction and packet-level data.
How can you enable VPC flow logs for an existing VPC?
To enable VPC flow logs for an existing VPC, navigate to the VPC dashboard in the AWS Management Console, select the VPC, then click on “Create flow log.” You can specify the level of data you want to collect and the destination for the logs, such as CloudWatch Logs or Amazon S
When designing a system to analyze VPC flow logs, which AWS services could be used for scalable log data processing and analysis?
For scalable log data processing and analysis, AWS services like Amazon CloudWatch Logs for monitoring and real-time analysis, Amazon Athena for ad-hoc querying, and Amazon Elasticsearch Service for more complex search and analytics are commonly used.
Can VPC flow logs be used to monitor IPv6 traffic in an AWS VPC?
Yes, VPC flow logs can capture both IPv4 and IPv6 traffic for ENIs (Elastic Network Interfaces) within the VPC. However, you must ensure that IPv6 is enabled for your VPC and associated with the subnets and ENIs you wish to monitor.
How can you ensure the security of your VPC flow log data when storing in Amazon S3?
You can ensure the security of VPC flow log data stored in Amazon S3 by using S3 bucket policies to restrict access, enabling Server-Side Encryption (SSE) for data encryption at rest, and optionally leveraging AWS KMS to manage encryption keys. Additionally, you can activate S3 access logging for audit trails.
What is the role of IAM (Identity and Access Management) in managing access to VPC flow logs?
IAM plays a critical role in managing access to VPC flow logs by defining policies that grant or restrict user and service permissions for actions like creating, configuring, and deleting flow logs, as well as accessing flow log data in CloudWatch Logs and Amazon S
Can you filter VPC flow logs? If so, how would you apply a filter to capture specific types of traffic or events?
Yes, you can filter VPC flow logs by applying filter patterns in CloudWatch Logs to specify which log events are of interest. For example, you can create a metric filter to capture SSH traffic by filtering for events with destination port In Amazon Athena, you can write SQL queries to filter for specific events.
What would be the implications of not specifying a filter when creating a VPC flow log?
Not specifying a filter when creating a VPC flow log means that all traffic, including both accepted and rejected packets, will be logged. This can lead to large volumes of data, which may increase costs and make it more challenging to identify relevant events during analysis.
How would you troubleshoot if your VPC flow logs are not showing any data?
If VPC flow logs are not showing any data, verify that the correct IAM role permissions are in place, check that the flow log is properly configured (with correct IDs and a log group destination), ensure that the network interfaces are active and have traffic, and review any associated VPC Security Group or NACL rules that might prevent traffic.
Is it possible to export VPC flow log data to an external analysis tool? If so, how?
Yes, VPC flow log data can be exported to external analysis tools by streaming it from CloudWatch Logs directly to Amazon Kinesis or by exporting the data to an Amazon S3 bucket, from which it can be downloaded or integrated with other data analysis tools.
Great explanation on VPC flow logs! I especially found the section on extended fields very helpful.
Can someone explain the difference between base and extended fields in VPC flow logs?
This blog post was really useful. Passed my ANS-C01 exam last week!
I am having trouble analyzing VPC flow logs in CloudWatch. Any tips?
Glad to see a detailed explanation on this topic. Helped me clarify some doubts.
Is it possible to export VPC flow logs directly to S3?
Thanks for the comprehensive guide. Looking forward to more such posts!
I didn’t find the section on analyzing flow logs detailed enough.