Vagrant: Ensure IP Subnet not in use by localhost

Vagrantfile

@@ -4,6 +4,8 @@
 # For help on using kubespray with vagrant, check out docs/developers/vagrant.md
 
 require 'fileutils'
+require 'ipaddr'
+require 'socket'
 
 Vagrant.require_version ">= 2.0.0"
 
@@ -99,6 +101,33 @@ $extra_vars ||= {}
 
 host_vars = {}
 
+def collect_networks(subnet, subnet_ipv6)
+  Socket.getifaddrs.filter_map do |iface|
+    next unless iface&.netmask&.ip_address && iface.addr
+
+    is_ipv6 = iface.addr.ipv6?
+    ip      = IPAddr.new(iface.addr.ip_address.split('%').first)
+    ip_test = is_ipv6 ? IPAddr.new("#{subnet_ipv6}::0") : IPAddr.new("#{subnet}.0")
+
+    prefix  = IPAddr.new(iface.netmask.ip_address).to_i.to_s(2).count('1')
+    network = ip.mask(prefix)
+
+    [IPAddr.new("#{network}/#{prefix}"), ip_test]
+  end
+end
+
+def subnet_in_use?(network_ips)
+  network_ips.any? { |net, test_ip| net.include?(test_ip) && test_ip != net }
+end
+
+network_ips = collect_networks($subnet, $subnet_ipv6)
+
+if subnet_in_use?(network_ips)
+  puts "Invalid subnet provided, subnet is already in use: #{$subnet}.0"
+  puts "Subnets in use: #{network_ips.inspect}"
+  exit 1
+end
+
 # throw error if os is not supported
 if ! SUPPORTED_OS.key?($os)
   puts "Unsupported OS: #{$os}"