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Troubleshooting and FAQ

Common errors​

The "Enable IPv6 dual-stack" checkbox is greyed out (disabled)​

Cause: The current VPC has stackMode = ipv4, or the dual-stack VPC is out of available /64 prefixes.

Solution:

  • Confirm the selected VPC has stackMode = dual — contact FPT Cloud if you don't have a dual-stack VPC.
  • If the VPC is dual but out of /64: contact FPT Cloud to create another VPC, or delete a dual-stack subnet no longer in use.

Can't create an Instance — the Create button is disabled​

Message: "IPv6 quota exhausted for this subnet" or a similar alert.

Cause: The selected subnet has ipv6Remaining = 0 — all IPv6 addresses have been allocated.

Solution: Select another dual-stack subnet with free IPv6 addresses. Check the IPv6 Remaining column in Subnet Detail.

No dual-stack VPC appears in the dropdown when creating a Subnet​

Cause: Your VPC hasn't been configured for dual-stack — all VPCs shown have stackMode = ipv4.

Solution: Contact FPT Cloud to request a dual-stack VPC configuration. See Request a Dual-Stack VPC from FPT Cloud.

Error "IPv6 must be within the subnet IPv6 CIDR"​

Cause: The manually entered IPv6 address is not within the subnet's /64 prefix.

Solution: Leave the IPv6 Address field empty so DHCPv6 assigns one, or enter a correctly formatted address within the CIDR range (for example, if the CIDR is 2401:db00:1100:a10::/64, the address must start with 2401:db00:1100:a10::).

Error "Invalid IPv6 CIDR" when creating a Security Group rule​

Cause: The source CIDR is not valid in IPv6 format when IP Type = IPv6.

Solution: Enter a correctly formatted IPv6 CIDR — for example, 2401:db00::/32 — or use the All IPv6 (::/0) preset.

The "Dual-stack" badge doesn't appear on a newly created Subnet​

Cause: The subnet was created with the Enable IPv6 dual-stack checkbox off.

Solution: IPv6 cannot be added to an existing subnet — delete the old subnet and recreate it with the checkbox on.

Frequently asked questions​

Q: Can I add IPv6 to a VPC I created earlier? A: stackMode cannot be changed after a VPC is created. If you want to convert an existing VPC to dual-stack or create a new dual-stack VPC, contact FPT Cloud for support — self-service creation of a dual-stack VPC is not available in Phase 1.

Q: Can I choose the /64 prefix for a subnet myself? A: No. The system automatically allocates a /64 prefix from the VPC's Parent Pool. It cannot be chosen manually.

Q: Can IPv6 Mode be changed to Static? A: No. Phase 1 supports only DHCPv6 Stateful. This mode is fixed.

Q: Can an Instance have multiple IPv6 addresses? A: Each NIC receives exactly one IPv6 address. To get more IPv6 addresses, add a new NIC to the instance.

Q: Is IPv6 billed separately? A: The IPv6 billing model is being confirmed with the Finance team. Contact Sales for more information before go-live.

Q: Why does the IPv6 Address column in the Instances List show empty/—? A: The instance's primary NIC belongs to an IPv4-only subnet. The instance can attach an additional NIC on a dual-stack subnet; the system does not yet support changing the primary NIC.

Contact support​

If the problem persists after trying the solutions above:

  • Check platform status: contact the Ops team to confirm IPv6 networking is enabled
  • Open a support ticket: provide the VPC name, subnet ID, and the specific error message