networkfirewall

Network Firewall

Overview

Domain expertise for configuring AWS Network Firewall, the managed stateful firewall and intrusion prevention service that filters traffic at the perimeter of a VPC using the Suricata inspection engine. Covers placing a firewall in the traffic path and routing traffic through its endpoints, centralizing inspection across VPCs with a transit gateway-attached firewall, filtering outbound traffic by domain name, logging and rule tuning, TLS inspection of encrypted traffic, and diagnosing why traffic is dropped, passed, or unmatched.

This skill is a router. Each customer task maps to a reference file under references/. Read the matching reference in full before acting, then follow its constraints and steps. The reference files are self-contained: each carries its own decision tables, constraints, procedure, and troubleshooting.

Execute commands using the AWS MCP server when connected (sandboxed execution, audit logging, observability). Fall back to the AWS CLI otherwise. Network Firewall is regional; pass --region matching the firewall's Region on every aws network-firewall command. Firewall creation, deletion, and several operations are asynchronous: poll the resource until it reaches the expected state before depending on it.

Which Network Firewall task do you need?

Goal	Reference
Place a firewall in the path and route VPC traffic through its endpoints	deploying a firewall and routing traffic through it
Inspect traffic across many VPCs from one place using a transit gateway-attached firewall	centralizing inspection with a transit gateway-attached firewall
Allow or block outbound connections by destination domain name	filtering outbound traffic by domain name
Turn on alert, flow, and TLS logging and tune rules from what they show	enabling firewall logging and tuning rules
Decrypt and inspect TLS traffic with ACM certificates	inspecting encrypted traffic with TLS inspection
Write custom stateful Suricata rules and fix rules that do not match	writing and troubleshooting stateful Suricata rules
Block a specific indicator immediately during an active security incident	responding to an active security incident
Manage the firewall, policy, and rules in CloudFormation or the CDK	managing firewall rules as IaC
Replace a third-party firewall appliance with Network Firewall	migrating from a third-party firewall appliance
Find out why traffic is dropped, passed, or not matching a rule	diagnosing dropped or unmatched traffic

Routing notes

• Deploy before rules. A firewall does nothing until VPC route tables redirect traffic to its endpoints, and nothing reports an error when the routing is missing. Route to the deploying reference first when the firewall is new or traffic is not reaching it, before assuming a rule problem.
• Transit gateway-attached vs inspection VPC. The centralizing reference uses the native transit gateway-attached firewall, which removes the hand-built inspection VPC and its route tables. Route there for multi-VPC or multi-account inspection rather than building an inspection VPC by hand.
• Domain filtering matches the handshake, not the IP. The domain filtering reference matches on the TLS SNI and HTTP host header, not on a DNS lookup, and an allow list silently drops non-matching traffic of the same protocol. Route there for outbound domain control, and reach for TLS inspection when the customer needs the full URL path rather than the domain.
• TLS inspection changes what rules match. The TLS inspection reference is the precondition for any rule that needs to act on decrypted payload. After TLS termination the decrypted traffic is plain HTTP to the stateful engine, so port-443 and tls rules stop matching. Route there before the customer writes rules against encrypted traffic.
• Diagnose by symptom, not by guess. The diagnosing reference reads the endpoint status message (error vs non-recoverable failure), tests routing symmetry, and checks HOME_NET, evaluation order, and rule layer before any rewrite. Route there for "traffic is dropped," "traffic passes when it should not," or "my rule does not match." When the symptom is "traffic dropped with no alert log at all," suspect post-quantum ClientHello fragmentation, covered in the diagnosing and logging references.
• Incident now vs configuration. The responding reference is for an active incident on an already-deployed firewall: block one indicator immediately, confirm it, and back it out. Route there for "I am under attack, block this now," not through the deploying or rule-authoring references, which are slower configuration workflows.
• Rule authoring vs domain filtering. The writing-Suricata reference covers custom stateful rules (flow keywords, rule order, Suricata engine constraints). Route there for IPS or IDS rule authoring; route to the domain filtering reference when the customer only needs to allow or block domains.
• IaC vs console changes. The managing-as-code reference is for CloudFormation or CDK ownership, where immutable properties (capacity, rule order) make the wrong structure a replacement. Route there when the customer manages the firewall in templates.
• Migration vs first-time setup. The migrating reference is for replacing a third-party firewall appliance with a live rule set and traffic path. Route there for "move off Palo Alto or FortiGate," not the deploying reference, which assumes a greenfield firewall.

Security Considerations

This skill manages network perimeter security, so a misconfiguration weakens the security posture of every VPC behind the firewall. Carry these into each task:

• Default-drop posture. You MUST configure a stateful default action of drop (an allow list of permitted traffic) rather than default-allow, so traffic that no rule matches is blocked rather than passed uninspected. For a network firewall a fail-closed default is a fundamental security control, not an option, and an overly permissive rule set degrades the firewall to a passthrough.
• No silent inspection gaps. You MUST confirm traffic is actually routed through the firewall endpoints and forwarded to the stateful engine; misconfigured route tables or a stateless default action other than aws:forward_to_sfe leave traffic uninspected with no error.
• Ephemeral, least-privilege credentials. You MUST use ephemeral, least-privilege credentials (a time-bound assumed-role session) scoped to the specific network-firewall: actions and resources each operator needs (e.g., network-firewall:UpdateRuleGroup, network-firewall:DescribeFirewall), never long-lived access keys or broad administrative access, since these permissions can change what traffic is allowed.
• Encrypt logs and firewall data at rest. You MUST encrypt every destination that receives firewall logs (alert, flow, or TLS), using a customer-managed AWS KMS key on Amazon CloudWatch Logs log groups (aws logs associate-kms-key), either SSE-S3 or a customer-managed AWS KMS key on Amazon S3 buckets, and a customer-managed AWS KMS key on Amazon Data Firehose delivery streams, because these logs expose sensitive network metadata (source and destination IPs, domain names, and SNI values). You SHOULD also encrypt the firewall's data at rest with a customer-managed AWS KMS key.
• Scope log-destination resource policies with condition keys. You SHOULD scope the resource policy on each log destination (the Amazon S3 bucket policy, the Amazon CloudWatch Logs resource policy, and the Amazon Data Firehose delivery-stream policy) with aws:SourceArn (the firewall's ARN) and aws:SourceAccount condition keys, so only this firewall in the expected account can write to the destination and another account or service cannot (confused-deputy prevention).
• Record API changes with CloudTrail. You SHOULD enable AWS CloudTrail on the account so firewall, policy, rule group, and logging-configuration API changes are recorded for audit and incident review.
• Alarm on critical firewall events. You SHOULD configure CloudWatch alarms to alert on critical firewall events (endpoint failures, policy changes, capacity warnings) so issues are detected and escalated promptly. You MUST encrypt any SNS topic used for these alarm notifications with a customer-managed AWS KMS key and restrict alarm notification recipients to authorized operations and security personnel, since alarm messages can expose sensitive firewall metadata (endpoint status, traffic patterns, and capacity).
• Per-task detail. Each reference carries its own Security Considerations for its workflow; read the matching reference before acting.

Additional Resources

• What is AWS Network Firewall? (AWS Network Firewall Developer Guide)
• How AWS Network Firewall works (AWS Network Firewall Developer Guide)
• AWS Network Firewall pricing