DNS collisions detection with F# Async Workflows

There is one more useful application of script from the “Explore local network with F# Async Workflows” post. During the check of the machine availability we can collect IP addresses of all machines. After that we can compare IPs of different host names for collision. It is a good way to understand what is going on in your network.

#r "System.DirectoryServices.dll"
open System
open System.Collections
open System.DirectoryServices
open System.Net.NetworkInformation
open System.Threading.Tasks

let hosts =
    use searcher =
        new DirectorySearcher(new DirectoryEntry(),
            Filter="(objectClass=computer)", PageSize=10000)
    (searcher.FindAll() :> IEnumerable)
    |> Seq.cast<SearchResult>
    |> Seq.map (fun x -> x.GetDirectoryEntry().Name)
    |> Seq.map (fun n -> n.Substring(n.IndexOf("=")+1))
    |> Seq.toList

let checkHosts hosts =
    let rec ping attempts (host:string) =
        async {
            let! pingResult =
                (new Ping()).SendPingAsync(host)
                |> Async.AwaitTask |> Async.Catch
            match pingResult with
            | Choice2Of2 e -> return None
            | Choice1Of2 reply when reply.Status = IPStatus.Success ->
                return Some(reply.Address.MapToIPv4().ToString())
            | _ when attempts > 0 -> return! ping (attempts-1) host
            | _ -> return None
        }
    let results =
        hosts
        |> Seq.map (ping 4)
        |> Async.Parallel
        |> Async.RunSynchronously
        |> Seq.toList
    List.zip results hosts

let dnsConflicts =
    hosts
    |> checkHosts
    |> List.filter (fst >> Option.isSome)
    |> Seq.groupBy fst
    |> Seq.filter (fun (_, seq) -> Seq.length seq > 1)
    |> Seq.map (fun (k, seq) ->
        (Option.get k, seq |> Seq.map snd |> Seq.toList) )
    |> Seq.toList