DHCP¶

When using managedTap, SR-IOV, or DPDK type networks, KubeVirt's built-in DHCP cannot function in these network modes. Kube-OVN leverages OVN's DHCP capabilities to configure DHCP options at both subnet and Pod levels, enabling virtual machines (VMs) under these network types to properly obtain IP addresses via DHCP. Additionally, Kube-OVN's DHCP supports advanced options such as DHCPv6, IPv6RA, DNS, and TFTP, allowing users to customize DHCP service behavior based on their needs.

Subnet-Level DHCP Configuration¶

The Subnet DHCP is configured as follows:

apiVersion: kubeovn.io/v1
kind: Subnet
metadata:
  name: sn-dual
spec:
  cidrBlock: "10.0.0.0/24,240e::a00/120"
  default: false
  disableGatewayCheck: true
  disableInterConnection: false
  excludeIps:
    - 10.0.0.1
    - 240e::a01
  gateway: 10.0.0.1,240e::a01
  gatewayNode: ''
  gatewayType: distributed
  natOutgoing: false
  private: false
  protocol: Dual
  provider: ovn
  vpc: vpc-test
  enableDHCP: true
  dhcpV4Options: "lease_time=3600,router=10.0.0.1,server_id=169.254.0.254,server_mac=00:00:00:2E:2F:B8"
  dhcpV6Options: "server_id=00:00:00:2E:2F:C5"
  enableIPv6RA: true
  ipv6RAConfigs: "address_mode=dhcpv6_stateful,max_interval=30,min_interval=5,send_periodic=true"

• enableDHCP: Whether to enable the DHCP function for the subnet.
• dhcpV4Options,dhcpV6Options: This field directly exposes DHCP-related options within ovn-nb, please read DHCP Options for more detail. The default value is "lease_time=3600, router=$ipv4_gateway, server_id=169.254.0.254, server_mac=$random_mac" and server_id=$random_mac.
• enableIPv6RA: Whether to enable the route broadcast function of DHCPv6.
• ipv6RAConfigs: This field directly exposes DHCP-related options within ovn-nb Logical_Router_Port, please read Logical Router Port for more detail. The default value is address_mode=dhcpv6_stateful, max_interval=30, min_interval=5, send_periodic=true.

Per-Pod DHCP Configuration¶

In addition to subnet-level DHCP configuration, Kube-OVN supports configuring DHCP options for each Pod's network interface individually via Pod annotations. Per-Pod DHCP configuration has the highest priority, overriding subnet-level DHCP settings, and is independent of the subnet's enableDHCP setting.

Annotation Format¶

# Primary network (provider="ovn")
ovn.kubernetes.io/dhcp-v4-options: "lease_time=3600,router=10.0.0.1,dns_server=8.8.8.8"
ovn.kubernetes.io/dhcp-v6-options: "server_id=00:00:00:00:00:01"

# Attachment network (provider="net1.ns1.ovn")
net1.ns1.ovn.kubernetes.io/dhcp-v4-options: "lease_time=7200"

The annotation key format is <provider>.kubernetes.io/dhcp-v4-options and <provider>.kubernetes.io/dhcp-v6-options, where <provider> is the network provider name. For the default network, the provider is ovn. For attachment networks added via Multus, the provider format is <net-attach-def-name>.<namespace>.ovn.

Usage Examples¶

The following example sets custom DHCPv4 options for a Pod:

apiVersion: v1
kind: Pod
metadata:
  name: dhcp-pod
  annotations:
    ovn.kubernetes.io/dhcp-v4-options: "lease_time=3600,router=10.0.0.1,dns_server=8.8.8.8"
    ovn.kubernetes.io/dhcp-v6-options: "server_id=00:00:00:00:00:01"
spec:
  containers:
    - name: test
      image: docker.io/library/nginx:alpine

For Multus multi-NIC scenarios, you can set DHCP options separately for each network interface by provider:

apiVersion: v1
kind: Pod
metadata:
  name: multi-nic-dhcp-pod
  annotations:
    k8s.v1.cni.cncf.io/networks: '[{"name": "net1", "namespace": "ns1"}]'
    ovn.kubernetes.io/dhcp-v4-options: "lease_time=3600,router=10.0.0.1"
    net1.ns1.ovn.kubernetes.io/dhcp-v4-options: "lease_time=7200,router=10.0.1.1"
spec:
  containers:
    - name: test
      image: docker.io/library/nginx:alpine

Priority¶

The DHCP options priority from highest to lowest is:

1. Pod annotations: DHCP options set via <provider>.kubernetes.io/dhcp-v4-options and <provider>.kubernetes.io/dhcp-v6-options.
2. Subnet configuration: DHCP options set via the dhcpV4Options and dhcpV6Options fields in the Subnet CRD.

When a Pod has DHCP annotations, the Pod-level DHCP configuration is used exclusively, ignoring the subnet-level settings.

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