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Subnet — Troubleshooting

CIDR Overlap Error When Creating a Subnet​

Symptom: When clicking confirm to create the subnet, the system displays an error similar to:

"The CIDR overlaps with an existing subnet in this VPC."

Cause: The CIDR range you entered overlaps (fully or partially) with an existing subnet in the same VPC.

Resolution:

  1. Return to the Network → Subnets list to view all CIDRs currently in use in the VPC.
  2. Select a different CIDR range that does not overlap with any existing subnet.
  3. Example: if 192.168.1.0/24 already exists, use 192.168.2.0/24 or another non-overlapping range.
  4. Enter the new CIDR and try creating again.

Cannot Delete a Subnet (Resources Still Attached)​

Symptom: Clicking to delete the subnet is refused by the system with an error message similar to:

"Cannot delete subnet: resources are still attached."

Cause: One or more virtual machines (instances) or other resources are still attached to this subnet. The system does not allow deleting a subnet while resources remain inside it.

Resolution:

  1. Navigate to VPC → Instances (or the relevant resource section) to find all resources using the subnet you want to delete.
  2. Stop and delete (or move to another subnet) all such resources.
  3. Return to Network → Subnets and delete the subnet.

Virtual Machine in an Isolated Subnet Cannot Connect to the Internet​

Symptom: A virtual machine in the subnet is completely unable to reach external addresses (ping, curl, and downloading updates all fail).

Cause: This is not an error — this is the expected, by-design behavior. An Isolated subnet is created with the explicit purpose of being fully isolated from the Internet. There is no routing path for traffic to exit the VPC.

Resolution:

  • If the virtual machine needs Internet access, you need to create a new subnet of type Routed and move or re-create the virtual machine in that subnet.
  • If the network isolation requirement still applies (for example, a database server), keep the Isolated type and establish internal communication channels (internal load balancer, VPC peering if needed) instead of direct Internet access.

Note: The subnet type (Routed/Isolated) cannot be changed after creation. A new subnet must be created if you want to change the type.

DNS Cannot Resolve Inside the Subnet​

Symptom: A virtual machine in the subnet cannot resolve domain names (for example: ping google.com returns Name or service not known) even though the Internet connection is working normally.

Cause: The Primary DNS field was not configured when the subnet was created, or the DNS address entered is invalid or unresponsive.

Resolution:

  1. Check the subnet's current DNS configuration on the subnet details page (DNS servers).
  2. If DNS is empty or invalid, you can configure DNS directly in the virtual machine's operating system (the /etc/resolv.conf file on Linux) as a temporary workaround.
  3. Commonly used DNS values:
    • Google Public DNS: 8.8.8.8 (Primary), 8.8.4.4 (Secondary)
    • Cloudflare DNS: 1.1.1.1 (Primary), 1.0.0.1 (Secondary)
  4. If you need to officially update the DNS for the subnet, contact the operations team for assistance (depending on the portal version, DNS editing may not yet be available through the interface).

Additional note: For Isolated subnets, even with DNS correctly configured, virtual machines cannot resolve public domain names unless the DNS server is located within the VPC or is reachable through another internal channel.