Direct answer
Google Cloud firewall evaluation depends on applicable rules, targets, direction and priority. Review the effective policy for the actual instance and validate representative traffic paths.
Map the affected workloads
Record the project, VPC network, instance identities or tags, applied firewall policies and owners. Capture ingress and egress rule direction, priority, action, protocol and source or destination. A rule may affect multiple instances through its target selection.
Reference: Google Cloud: VPC firewall rules.
Compare with the design
For a test application that needs traffic only from a proxy tier, compare the effective rule set with the agreed flow. Consider routes, public addresses and host firewall separately. Review hierarchical or other network policies that apply in the deployment.
- Check relevant IPv4 and IPv6 ranges.
- Identify stale tags and ownerless rules.
- Record legitimate management and recovery paths.
Run bounded connectivity checks
Use authorized test instances and a known-good listener to verify one allowed and one prohibited source. Collect provider logs where configured and distinguish an unavailable service from a network denial. Avoid broad or high-rate scans unless included in scope.
Pilot and retest
Change rules through the owner's approved deployment and test the intended application function and blocked path. Review all affected targets before rollout and preserve a rollback plan for critical connectivity.
Assessment limits
Effective network behavior can include hierarchical policy, VPC rules, routing, host firewall and service authentication. A sample connection does not establish every path's behavior.
Frequently asked questions
Does a firewall rule apply to every instance?
Not necessarily. Its targets and applicable policy determine which instances are affected.
Does a timeout prove a firewall denied the request?
No. Verify a listening service and inspect available network logs or diagnostics.
Primary sources and further reading
These guides combine published security guidance with practical assessment planning. Adapt checks to the owner's policy, environment, and authorized scope.
This guide was prepared with AI assistance using the linked sources and illustrative examples. Check current vendor guidance and your environment before making changes.