ipam

#!/usr/bin/env bash
# Create veth pair
ip link add veth-host type veth peer name veth-container

# Move the container end into the container netns
ip link set veth-container netns <namespace>

# Assign IP address inside the container namespace
ip -n <namespace> addr add 10.244.1.5/24 dev veth-container

# Bring up interfaces
ip -n <namespace> link set veth-container up
ip link set veth-host up

# (On teardown) Delete the veth pair
ip link del veth-host

#!/usr/bin/env bash
# Example: retrieve a free IP from a file-based allocator (simplified)
ip=$(get_free_ip_from_file "/var/lib/cni/networks/mynet")

# OR: invoke the host-local IPAM plugin (the plugin returns JSON with the allocated IP)
# The actual invocation is performed by the CNI runtime calling the IPAM plugin binary
ip_json=$(./host-local < /etc/cni/net.d/net-script.conf)
ip=$(jq -r '.ips[0].address' <<< "$ip_json")

# Assign IP to the container interface
ip -n <namespace> addr add "$ip" dev veth-container

# Add routes (e.g., default route) inside the namespace
ip -n <namespace> route add default via 10.244.0.1

$ cat /etc/cni/net.d/net-script.conf
{
  "cniVersion": "0.2.0",
  "name": "mynet",
  "type": "net-script",
  "bridge": "cni0",
  "isGateway": true,
  "ipMasq": true,
  "ipam": {
    "type": "host-local",
    "subnet": "10.244.0.0/16",
    "routes": [
      { "dst": "0.0.0.0/0" }
    ]
  }
}

{
  "cniVersion": "0.2.0",
  "ips": [{ "version": "4", "address": "10.244.1.5/24", "gateway": "10.244.0.1" }],
  "routes": [{ "dst": "0.0.0.0/0" }]
}