Multi-Cluster IP Address Management (IPAM)

Multi-Cluster IPAM is a feature responsible for automating the allocation of IP address ranges/subnets per user-cluster, based on a predefined configuration (IPAMPool) per datacenter that defines the pool subnet and the allocation size. The user cluster allocated ranges are available in the KKP Addon TemplateData, so it can be used by various Addons running in the user cluster.

Motivation and Background

Networking applications deployed in KKP user clusters need automated IP Address Management (IPAM) for IP ranges that they use, in a way that prevents address overlaps between multiple user clusters. An example for such an application is MetalLB load-balancer, for which a unique IP range from a larger CIDR range needs to be configured in each user cluster in the same datacenter.

The goal is to provide a simple solution that is automated and less prone to human errors.

Allocation Types

Each IPAM pool in a datacenter should define an allocation type: “range” or “prefix”.


Results in a set of IPs based on an input size.

E.g. the first allocation for a range of size 8 in a pool subnet would be

Note: There is a minimal allowed pool subnet mask based on the IP version (20 for IPv4 and 116 for IPv6). So, if you need a large range of IPs, it’s recommended to use the “prefix” type.


Results in a subnet of the pool subnet based on an input subnet prefix. Recommended when a large range of IPs is necessary.

E.g. the first allocation for a prefix 30 in a pool subnet would be

and the second would be

Input Resource (IPAMPool)

KKP exposes a global-scoped Custom Resource Definition (CRD) IPAMPool in the seed cluster. The administrators are able to define the IPAMPool CR with a specific name with multiple pool CIDRs with predefined allocation ranges tied to specific datacenters. The administrators can also manage the IPAM pools via API endpoints (/api/v2/seeds/{seed_name}/ipampools).

E.g. containing both allocation types for different datacenters:

kind: IPAMPool
  name: metallb
      type: range
      poolCidr: ""
      allocationRange: 8
      type: prefix
      poolCidr: ""
      allocationPrefix: 30

Note that poolCIDR can be the same in different datacenters.


Required IPAMPool spec fields:

  • datacenters list cannot be empty.
  • type for a datacenter is mandatory.
  • poolCidr for a datacenter is mandatory.
  • allocationRange for a datacenter with “range” allocation type is mandatory.
  • allocationPrefix for a datacenter with “prefix” allocation type is mandatory.

For the “range” allocation type:

  • allocationRange should be a positive integer and cannot be greater than the pool subnet possible number of IP addresses.
  • IPv4 poolCIDR should have a prefix (i.e. mask) equal or greater than 20.
  • IPv6 poolCIDR should have a prefix (i.e. mask) equal or greater than 116.

For the “prefix” allocation type:

  • allocationPrefix should be between 1 and 32 for IPv4 pool, and between 1 and 128 for IPv6 pool.
  • allocationPrefix should be equal or greater than the pool subnet mask size.


In general, modifications of the IPAMPool are not allowed, with the following exceptions:

  • It is possible to add a new datacenter into the IPAMPool.
  • It is possible to delete a datacenter from the IPAMPool, if there is no persisted allocation (IPAMAllocation) in any user cluster for it.

If you need to change an already applied IPAMPool, you should first delete it and then apply it with the changes. Note that by IPAMPool deletion, all user clusters allocations (IPAMAllocation) will be deleted as well.

Generated Resource (IPAMAllocation)

The IPAM controller in the seed-controller-manager is in charge of the allocation of IP ranges from the defined pools for user clusters. For each user cluster which runs in a datacenter for which an IPAMPool is defined, it will automatically allocate a free IP range from the available pool.

The persisted allocation is an IPAMAllocation CR that will be installed in the seed cluster in the user cluster’s namespace.

E.g. for “prefix” type:

kind: IPAMAllocation
  name: metallb
  namespace: cluster-kd8jnt7gjj
  cidr: ""
  dc: aws-eu-central-1a
  type: prefix

E.g. for “range” type:

kind: IPAMAllocation
  name: metallb
  namespace: cluster-sd87xtqpnm
  - ""
  dc: azure-westeurope
  type: range

Note that the ranges of addresses may be disjoint for the “range” type, e.g.:

  - ""
  - ""

The reason for that is to allow for some IPAMPool modifications (i.e. increase of the allocation range) in the future.

Allocations Cleanup

The allocations (i.e. IPAMAllocation CRs) for a user cluster are deleted in two occasions:

  • Related pool (i.e. IPAMPool CR with same name) is deleted.
  • User cluster itself is deleted.

KKP Addon Template Integration

The user cluster allocated ranges (i.e. IPAMAllocation CRs values) are available in the Addon template data (attribute .Cluster.Network.IPAMAllocations) to be rendered in the Addons manifests. That allows consumption of the user cluster’s IPAM allocations in any KKP Addon.

For example, looping over all user cluster IPAM pools allocations in an addon template can be done as follows:


{{- range $ipamPool, $allocation := .Cluster.Network.IPAMAllocations }}
{{ $ipamPool }}:
  {{- if eq $allocation.Type "prefix" }}
  CIDR: {{ $allocation.CIDR }}
  {{- end }}
  {{- if eq $allocation.Type "range" }}
    {{- range $allocation.Addresses }}
    - {{ . }}
    {{- end }}
  {{- end }}
{{- end }}

MetalLB Addon Integration

KKP provides a MetalLB accessible addon integrated with the Multi-Cluster IPAM feature.

The addon deploys standard MetalLB manifests into the user cluster. On top of that, if an IPAM allocation from an IPAM pool with a specific name is available for the user-cluster, the addon automatically installs the equivalent MetalLB IP address pool in the user cluster (in the IPAddressPool custom resource from the API).

The KKP IPAMPool from which the allocations are made need to have the following name:

  • metallb if a single-stack (either IPv4 or IPv6) IP address pool needs to be created in the user cluster.
  • metallb-ipv4 and metallb-ipv6 if a dual-stack (both IPv4 and IPv6) IP address pool needs to be created in the user cluster. In this case, allocations from both address pools need to exist.

The created IPAddressPool custom resource (from the API) will have the following name:

  • kkp-managed-pool in case of a single-stack address pool,
  • kkp-managed-pool-dualstack in case of a dual-stack address pool.

Both address pools (single-stack and dual-stack) can co-exist in the same cluster.

For the reference, the Addon manifests can be found in the addons/metallb/ folder of the KKP source code.