/// <summary>
/// Function to be called recursively for FewestConsecutiveSubnetsFor
/// Works by verifying that passed subnet isn't bounded by head, tail
/// if not breaks subnet in half and recursively tests, building in essence a binary tree of testable subnet paths
/// </summary>
/// <param name="headIP">the head IP</param>
/// <param name="tailIP">the tail IP</param>
/// <param name="subnet">The subnet found on success</param>
/// <returns>true on success</returns>
private static IEnumerable <Subnet> FilledSubnets([NotNull] IPAddress headIP,
[NotNull] IPAddress tailIP,
[NotNull] Subnet subnet)
{
var networkPrefixAddress = subnet.NetworkPrefixAddress;
var broadcastAddress = subnet.BroadcastAddress;
// the given subnet is the perfect size for the head/tail (not papa bear, not mama bear, but just right with baby bear)
if (networkPrefixAddress.ToUnsignedBigInteger() >= headIP.ToUnsignedBigInteger() &&
broadcastAddress.ToUnsignedBigInteger() <= tailIP.ToUnsignedBigInteger())
{
return(new[] { subnet });
}
// increasing the route prefix by 1 creates a subnet of half the initial size (due 2^(max-n) route prefix sizing)
var nextSmallestRoutePrefix = subnet.RoutingPrefix + 1;
// over-iterated route prefix, no valid subnet beyond this point; end search on this branch
if ((subnet.IsIPv6 && nextSmallestRoutePrefix > 128) ||
(subnet.IsIPv4 && nextSmallestRoutePrefix > 32))
{
return(Enumerable.Empty <Subnet>()); // no subnets to be found here, stop investigating branch of tree
}
// build head subnet
var headSubnet = new Subnet(networkPrefixAddress, nextSmallestRoutePrefix);
// use the next address after the end of the head subnet as the first address for the tail subnet
var tailStartingAddressBigInteger = headSubnet.BroadcastAddress.ToUnsignedBigInteger() + 1;
IPAddress tailStartingAddress;
if (!IPAddressUtilities.TryParse(tailStartingAddressBigInteger, headIP.AddressFamily, out tailStartingAddress))
{
throw new ArgumentException();
}
var tailSubnet = new Subnet(tailStartingAddress, nextSmallestRoutePrefix);
// break into binary search tree, searching both head subnet and tail subnet for ownership of head and tail ip
return(FilledSubnets(headIP, tailIP, headSubnet)
.Concat(FilledSubnets(headIP, tailIP, tailSubnet)));
}
