MetalLB remains idle until configured. This is accomplished by creating and deploying a configmap into the same namespace (metallb-system) as the deployment.
There is an example configmap in
annotated with explanatory comments.
If you’ve named the configmap
config.yaml, you can deploy the manifest with
kubectl apply -f config.yaml.
The specific configuration depends on the protocol(s) you want to use to announce service IPs. Jump to:
Layer 2 mode is the simplest to configure: in many cases, you don’t need any protocol-specific configuration, only IP addresses.
Layer 2 mode does not require the IPs to be bound to the network interfaces of your worker nodes. It works by responding to ARP requests on your local network directly, to give the machine’s MAC address to clients.
For example, the following configuration gives MetalLB control over
192.168.1.250, and configures Layer 2
apiVersion: v1 kind: ConfigMap metadata: namespace: metallb-system name: config data: config: | address-pools: - name: default protocol: layer2 addresses: - 192.168.1.240-192.168.1.250
For a basic configuration featuring one BGP router and one IP address range, you need 4 pieces of information:
As an example, if you want to give MetalLB the range 192.168.10.0/24 and AS number 64500, and connect it to a router at 10.0.0.1 with AS number 64501, your configuration will look like:
apiVersion: v1 kind: ConfigMap metadata: namespace: metallb-system name: config data: config: | peers: - peer-address: 10.0.0.1 peer-asn: 64501 my-asn: 64500 address-pools: - name: default protocol: bgp addresses: - 192.168.10.0/24
By default, BGP mode advertises each allocated IP to the configured
peers with no additional BGP attributes. The peer router(s) will
/32 route for each service IP, with the BGP localpref
set to zero and no BGP communities.
You can configure more elaborate advertisements by adding a
bgp-advertisements section that lists one or more custom
In addition to specifying localpref and communities, you can use this
to advertise aggregate routes. The
option lets you “roll up” the /32s into a larger prefix. Combined with
multiple advertisement configurations, this lets you create elaborate
advertisements that interoperate with the rest of your BGP network.
For example, let’s say you have a leased
/24 of public IP space, and
you’ve allocated it to MetalLB. By default, MetalLB will advertise
each IP as a /32, but your transit provider rejects routes more
/24. So, you need to somehow advertise a
/24 to your
transit provider, but still have the ability to do per-IP routing
Here’s a configuration that implements this:
apiVersion: v1 kind: ConfigMap metadata: namespace: metallb-system name: config data: config: | peers: - peer-address: 10.0.0.1 peer-asn: 64501 my-asn: 64500 address-pools: - name: default protocol: bgp addresses: - 198.51.100.0/24 bgp-advertisements: - aggregation-length: 32 localpref: 100 communities: - no-advertise - aggregation-length: 24 bgp-communities: no-advertise: 65535:65282
With this configuration, if we create a service with IP 198.51.100.10, the BGP peer(s) will receive two routes:
198.51.100.10/32, with localpref=100 and the
no-advertisecommunity, which tells the peer router(s) that they can use this route, but they shouldn’t tell anyone else about it.
198.51.100.0/24, with no custom attributes.
With this configuration, the peer(s) will propagate the
198.51.100.0/24 route to your transit provider, but once traffic
shows up locally, the
198.51.100.10/32 route will be used to forward
into your cluster.
As you define more services, the router will receive one “local”
for each of them, as well as the covering
/24. Each service you
define “generates” the
/24 route, but MetalLB deduplicates them all
down to one BGP advertisement before talking to its peers.
The above configuration also showcases the
configuration section, which lets you define readable names for BGP
communities that you can reuse in your advertisement
configurations. This is completely optional, you could just specify
65535:65281 directly in the configuration of the
/24 if you
By default, every node in the cluster connects to all the peers listed in the configuration. In more advanced cluster topologies, you may want each node to connect to different routers. For example, if you have a “rack and spine” network topology, you likely want each machine to peer with its top-of-rack router, but not the routers in other racks.
You can limit peers to certain nodes by using the
attribute of peers in the configuration. The semantics of these
selectors are the same as those used elsewhere in Kubernetes, so refer
labels documentation on
the Kubernetes website.
For example, this is a (somewhat contrived) definition for a peer that will only be used by machines:
rack=frontendlabel, but not the label
peers: - peer-address: 10.0.0.1 peer-asn: 64501 my-asn: 64500 node-selectors: - match-labels: rack: frontend match-expressions: - key: network-speed operator: NotIn values: [slow] - match-expressions: - key: kubernetes.io/hostname operator: In values: [hostA, hostB]
In some environments, you’ll have some large address pools of “cheap” IPs (e.g. RFC1918), and some smaller pools of “expensive” IPs (e.g. leased public IPv4 addresses).
By default, MetalLB will allocate IPs from any configured address pool with free addresses. This might end up using “expensive” addresses for services that don’t require it.
To prevent this behaviour you can disable automatic allocation for a pool
by setting the
auto-assign flag to
# Rest of config omitted for brevity address-pools: - name: cheap protocol: bgp addresses: - 192.168.144.0/20 - name: expensive protocol: bgp addresses: - 126.96.36.199/30 auto-assign: false
Addresses can still be specifically allocated from the “expensive” pool with the methods described in the usage section.
Some old consumer network equipment mistakenly blocks IP addresses
.255, because of
If you encounter this issue with your users or networks, you can set
avoid-buggy-ips: true on an address pool to mark
addresses as unusable.