could not find any non-overlapping CIDRs in parent…

Error message

could not find any non-overlapping CIDRs in parent NetworkCIDR; cannot automatically assign CIDR to subnet

What it means

kOps splits the parent NetworkCIDR into candidate child CIDRs and filters out ones overlapping with explicitly-specified (reserved) subnets. When every candidate overlaps or the parent is too small, automatic CIDR assignment is impossible, so kOps refuses to guess and fails loudly.

Solutions

Enlarge cluster.spec.networkCIDR (or add a non-overlapping additionalNetworkCIDR) so free space remains
Remove or shrink explicit subnet CIDRs that reserve overlapping space, letting kOps carve them automatically
Move some subnets onto a separate networkCIDR / delete unused subnets before re-running update

Example fix

// before
spec:
  networkCIDR: 10.0.0.0/28  # too small for all subnets
// after
spec:
  networkCIDR: 10.0.0.0/16

Defensive patterns

Strategy: validation

Validate before calling

_, network, _ := net.ParseCIDR(c.Spec.NetworkCIDR)
var reserved []*net.IPNet
for _, s := range c.Spec.Networking.Subnets {
	if s.CIDR != "" {
		if _, sn, err := net.ParseCIDR(s.CIDR); err == nil { reserved = append(reserved, sn) }
	}
}
// ensure network has room outside all reserved subnets before auto-assign

Type guard

func hasFreeSpace(network *net.IPNet, reserved []*net.IPNet) bool {
	for _, r := range reserved { if subnet.SubnetContains(network, r) && r.String() == network.String() { return false } }
	return true
}

Try / catch

if err := PerformAssignments(c, cloud); err != nil {
	if strings.Contains(err.Error(), "non-overlapping CIDRs") { /* enlarge networkCIDR or drop explicit CIDRs */ }
	return err
}

Prevention

Plan networkCIDR size for current + future subnet count before cluster creation
Avoid specifying explicit CIDRs for every subnet; mix explicit and auto-allocated
Re-check capacity when adding AZs or subnets

When it happens

Trigger: Auto-allocation requested (subnets without cidr) while the parent networkCIDR is too small or fully consumed by explicitly reserved subnet CIDRs — e.g. a /24 network with reserved subnets covering all of it.

Common situations: Cluster grown over time until explicitly-assigned subnet CIDRs exhaust the networkCIDR; shrinking networkCIDR during an upgrade; many utility/internal subnets each reserving space.

Related errors

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/058c16e10c10a733. Report an issue: GitHub.

Appendix: source

Thrown at upup/pkg/fi/cloudup/subnets.go:209

	// Remove any CIDRs marked as overlapping
	{
		var nonOverlapping []*net.IPNet
		for _, c := range bigCIDRs {
			overlapped := false
			for _, r := range reserved {
				if subnet.Overlap(r, c) {
					overlapped = true
				}
			}
			if !overlapped {
				nonOverlapping = append(nonOverlapping, c)
			}
		}
		bigCIDRs = nonOverlapping
	}

	if len(bigCIDRs) == 0 {
		return fmt.Errorf("could not find any non-overlapping CIDRs in parent NetworkCIDR; cannot automatically assign CIDR to subnet")
	}

	// Assign CIDRs to little subnets
	if len(littleSubnets) > 0 {
		littleCIDRs, err := subnet.SplitInto8(bigCIDRs[0])
		if err != nil {
			return err
		}
		bigCIDRs = bigCIDRs[1:]

		for _, subnet := range littleSubnets {
			if subnet.CIDR != "" {
				continue
			}

			if len(littleCIDRs) == 0 {
				return fmt.Errorf("insufficient (little) CIDRs remaining for automatic CIDR allocation to subnet %q", subnet.Name)
			}

View on GitHub (pinned to 4c8573c808)