Tighten VPC peering configuration so that route tables only allow traffic to explicitly required CIDR ranges, removing overly broad or unnecessary routes. The plan inventories your existing VPC peering connections and related route tables, guides you through defining which CIDR ranges truly need connectivity over each peering, then adjusts and validates routes so that only those CIDRs are reachable. Finally, it supports application-level testing and sign-off to confirm that required traffic still flows and unintended access is removed.
Identify all VPC peering connections you want to manage and capture their key attributes. This includes deciding which Regions and VPCs are in scope, listing all peering connections in those Regions, and recording requester/accepter VPC IDs, Regions, statuses, and relevant tags. Only active or otherwise usable peering connections are carried forward, and the results are stored in a structured format for later analysis.
From the set of requester and accepter VPCs, gather all associated route tables. For each route table, record its ID, VPC ID, whether it is the main route table, subnet associations, and any tags. This creates a complete picture of which route tables could contain routes over the in-scope VPC peerings.
For every in-scope route table, list all route entries and identify those that target VPC peering connections. For each peering route, capture the destination CIDR blocks (IPv4/IPv6), the peering connection ID, the route state, and its associated VPC and Region. These routes are linked back to the corresponding peering connection and stored so they can be compared to the required CIDR ranges you will define.
Guide you through specifying which CIDR ranges must be reachable over each peering, from each side. You are presented with the list of active peering connections, including their VPCs, Regions, tags, and the currently configured peering routes (with main vs explicitly associated route tables called out). For each connection, you define which CIDRs in the peer (or connected networks) need reachability from the requester, and optionally a different set of CIDRs needed from the accepter side. You can provide granular or aggregated CIDRs and add notes about special routing needs (for example, limiting certain subnets to specific route tables). These requirements are captured in a structured mapping per peering and per side.
Compare the existing peering routes against your required CIDR mappings to classify routes. Each route is analyzed to see if it exactly matches, is more specific than, or is broader than the required ranges—or falls outside them entirely. Routes are tagged as required, overly broad (for example, a /16 when only a few /24s are needed), or unnecessary (no overlap with required CIDRs). A candidate list of overly broad and unnecessary routes is created, along with the set of required routes to be preserved.
Use the candidate list to safely remove or adjust routes that extend beyond what you actually need. Before removing anything, the plan verifies that each required CIDR either already has an appropriate specific route or is scheduled to receive one. Routes classified as unnecessary are slated for deletion, and overly broad routes are removed or replaced once equivalent specific routes are in place. Route table updates are then applied to remove the selected routes. Afterward, updated route tables are checked to confirm removals, and any routes that cannot be removed are documented with reasons and follow-up recommendations.
Ensure that all required CIDR ranges are explicitly and correctly routed via peering in the appropriate route tables. Using your required CIDR definitions and the current state of peering routes, the plan determines which route tables must carry routes to each required CIDR. Existing routes are checked for correctness (CIDR, target peering connection, route state); compliant routes are left unchanged, while incorrect or blackholed routes are updated. Missing routes are added with the correct CIDR and peering target, while avoiding conflicting or ambiguous overlaps. After changes, route tables are rechecked so that every required CIDR has an active, correct route in each designated route table, and the final set of created or updated routes is recorded.
Re-scan all relevant route tables and verify that peering routes align with the required CIDR definitions. For each peering connection and each side, confirm that every required CIDR has at least one active route via the correct peering connection in all designated route tables. Also confirm that no remaining peering routes are broader than or outside the union of required CIDRs, unless explicitly intended, and that there are no routes to unintended networks via any peering connection. Any discrepancies are documented with recommended remediation, and a summary indicates which route tables are fully compliant and which still need adjustments.
Support application owners and network operators in confirming real-world connectivity. They receive a summary of each peering and its required CIDR ranges, then run connectivity tests (such as ping, traceroute, or application-level checks) between instances or services across the peered VPCs for representative CIDRs. They verify that expected paths are working and that access to non-required networks is not available. Any issues or unexpected reachability are reported for follow-up, and final user sign-off (or documented outstanding issues) confirms that connectivity now matches the defined routing requirements.