Certified - CompTIA Cloud+

Network configuration is a critical element of cloud service reliability. When access control lists, subnet definitions, or peering relationships are misconfigured, the result is often complete communication failure between cloud resources. These issues may show up as unreachable hosts, failed connections, or timeouts across internal services. Because cloud environments rely heavily on dynamic and distributed architecture, diagnosing network failures requires deep awareness of how routing, access policies, and IP planning interact. In this episode, we’ll walk through how to identify and resolve core network misconfigurations that impact cloud availability.
The Cloud Plus exam expects candidates to troubleshoot complex networking problems involving access controls, subnetting design, and peering logic. You may be given diagrams of broken flows, denied packet paths, or scenarios where two systems can’t communicate despite appearing connected. Success on the exam requires fluency in VPC layout analysis, layered access policy troubleshooting, and peering validation techniques. The ability to reason through isolation logic and identify rule conflicts is central to resolving cloud networking issues effectively and consistently.
Access control lists function as stateless packet filters at the subnet or network interface level. Misordered or conflicting rules within ACLs are a common cause of dropped traffic. If an allow rule is missing or overridden by a deny rule earlier in the rule set, communication between services can silently fail. Reviewing the ACLs assigned to the interface and examining logs for dropped packets can help isolate these failures. Cloud professionals must understand rule order, directionality, and protocol scope when troubleshooting stateless ACL behavior.
Subnet masks and CIDR ranges define how IP addresses are segmented within a virtual network. If these are misconfigured, services may fall into overlapping or unreachable ranges, causing routing failures or isolation between components. Confirming the correctness of subnet masks, address allocations, and IP utilization using tools like subnet calculators helps detect improper configurations. Cloud administrators should ensure that subnet CIDR blocks are large enough to support growth but do not collide with other defined ranges.
Subnet overlap across regions or peered VPCs is a serious issue that can disrupt routing. Peering connections rely on distinct, non-overlapping CIDR ranges in order to establish clean route propagation between environments. If two peered VPCs contain the same subnet range, routing tables will discard conflicting routes or ignore them entirely. Prior to establishing a peering relationship, administrators must review address allocations and adjust overlapping ranges to ensure compatibility between VPCs.
Security groups and ACLs often interact in cloud environments, with each enforcing access rules at different layers. Security groups are stateful, remembering traffic flow direction, while ACLs are stateless and must explicitly allow both inbound and outbound directions. If both are applied to the same resource, and one permits while the other denies a flow, communication may break unexpectedly. Candidates must be able to analyze both layers and ensure that each permits the required ports, protocols, and IP directions for valid flows to complete.
Virtual private cloud peering requires symmetrical configuration across both endpoints. If one side accepts the peering connection but does not update its route table or security policies, traffic may flow in one direction only or fail entirely. Monitoring the health of peering links, confirming that routes exist for the remote CIDR blocks, and validating security group alignment are critical. Bidirectional communication testing, using tools like ping or traceroute, helps verify whether the peering relationship is functional on both ends.
Route tables dictate where traffic flows within and between VPCs. If a route table is missing an entry for a connected subnet, or if the route points to an incorrect target, traffic will fail to reach its destination. Conflicting or overlapping routes may also override intended paths, especially in complex environments. Cloud administrators should audit each route table to ensure that all necessary CIDR blocks are present and pointing to the correct gateway or peering connection. Route propagation must be enabled where applicable.
DHCP options and DNS resolution settings control how services discover each other and receive internal IP addresses. If these are misconfigured, services may receive incorrect DNS server addresses or be assigned out-of-scope IPs. This leads to broken name resolution and service discovery failures. Reviewing DHCP scopes, DNS server settings, and hostname assignment policies at the VPC or subnet level is necessary when troubleshooting discovery issues. These foundational elements must be validated before higher-level services can reliably communicate.
Port accessibility tests are essential when diagnosing inter-subnet communication failures. Tools like telnet, nc, and Nmap can simulate connection attempts and reveal whether a port is open, closed, or filtered. These tests should be run from the source system targeting the intended destination, checking both the protocol and port number. If the connection fails, administrators should verify ACLs, security group rules, NAT behavior, and the current state of any peering or VPN link. Port scanning also helps reveal whether a service is running as expected on its assigned address and port.
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Cloud network failures are sometimes caused by IP address assignment issues. When dynamic host configuration protocol scopes are exhausted, new instances may fail to obtain addresses, resulting in connectivity loss. Static IP assignment errors can also lead to conflicts or unreachable resources if the same address is used by more than one interface or service. Candidates must confirm that assigned IP ranges have sufficient free space and that static IP reservations match interface expectations. Reviewing DHCP logs and checking current address pools is essential when diagnosing these availability issues.
Cloud firewalls, often implemented as centralized Firewall-as-a-Service platforms, may override or supplement local ACL configurations. These firewalls may apply to all traffic entering or leaving a region or account boundary, introducing additional rules that aren’t visible at the VPC level. When traffic is blocked unexpectedly, administrators should examine flow logs, firewall policy logs, and hit count reports to see which rule applied. It is important to validate logging and alerting settings so that drops are detectable, rather than silent.
Cross-account peering introduces another layer of complexity. In multi-tenant or multi-account environments, peering connections must be explicitly accepted, and permissions must be correctly scoped. IAM roles must allow the creation and acceptance of peering requests, and routing tables must be updated on both sides. Peering status alone does not guarantee reachability—both ends must be active, properly routed, and authorized. Candidates should test from both accounts and confirm that routes and rules are symmetrical and functional.
When traffic flows in only one direction between two systems, asymmetric routing or ACL configurations are often the culprit. Stateless ACLs must be configured to allow return traffic explicitly, while security groups, being stateful, manage this automatically. Asymmetric NAT rules or mismatched peering routes can also prevent replies from returning. One-way issues require bidirectional testing tools like traceroute or tcpdump to follow the packet path and determine where return traffic is being dropped or rerouted incorrectly.
Microsegmentation and subnet-level isolation are powerful tools for reducing risk, but they can also cause accidental disconnection of legitimate traffic. If traffic is segmented by tag, group, or subnet and a required path is blocked, services may fail silently. Candidates should reassess segmentation policies carefully, reviewing whether the level of isolation matches the organization’s intent. While it's tempting to remove segmentation to resolve an issue, cloud professionals must validate that such changes do not compromise the architecture’s overall security model.
Any time ACLs, subnet ranges, or peering relationships are adjusted, those changes must be documented. Rule updates, peering approvals, and routing modifications should be logged in version-controlled files or recorded through configuration management platforms. Diagrams of updated VPC architecture and exports of routing and access policies help future troubleshooting. Proper documentation ensures consistency, audit readiness, and collaboration among team members working across different segments of the cloud network.
Over time, even well-planned network configurations may drift. Rules may be added for temporary needs and not removed, or overlapping subnets may be introduced by mistake. Using configuration management tools to track the current state of network settings allows cloud teams to detect unauthorized or accidental changes. Alerts should be configured to identify when rule sets or address layouts deviate from known baselines. Periodic review of these baselines helps ensure ongoing compliance and avoids configuration entropy.
Automating the validation of key network paths reduces the risk of silent failure. Synthetic probes can test reachability between subnets or across peered VPCs on a scheduled basis. Tools like AWS Reachability Analyzer or Azure Network Watcher support these tests and help confirm expected flows after a deployment or rule change. Cloud teams should integrate connectivity checks into CI/CD pipelines or post-deployment procedures to ensure that changes do not break service interconnectivity.
The foundation of stable network configuration is consistent design and cautious expansion. Cloud professionals should implement standard IP planning, enforce layered security, and use visual tools to understand their architectures. Before deployment, all routes and access policies should be validated through simulation or live tests. During operations, default-deny postures should be applied and only the necessary flows opened to support function. The Cloud Plus exam will expect candidates to demonstrate knowledge of these best practices in both troubleshooting and network design scenarios.