Use this class to obtain the ip on different platforms including HoloLens using Unity3D as a development platform.

IpManager.cs

using System.Collections.Generic;
using System.Net.NetworkInformation;
using System.Net.Sockets;
#if WINDOWS_UWP
using Windows.Networking.Connectivity;
using Windows.Networking;
#endif

/// <summary>
/// Get the ip of the actual device. Also works on UWP (e.g. HoloLens).
/// 
/// Michael Falk
/// </summary>
public static class IpManager
{
    public enum AddressType
    {
        IPv4, IPv6
    }

    public static string GetIp(AddressType type)
    {
        string ip = "";
#if WINDOWS_UWP
        foreach (HostName localHostName in NetworkInformation.GetHostNames())
        {
            if (localHostName.IPInformation != null)
            {
                if (localHostName.Type == HostNameType.Ipv4)
                {
                    ip = localHostName.ToString();
                    break;
                }
            }
        }
#else
        List<string> IPs = GetAllIPs(type, false);
        if (IPs.Count > 0)
        {
            ip = IPs[IPs.Count - 1];
        }
#endif
        return ip;
    }

#if !WINDOWS_UWP
    public static List<string> GetAllIPs(AddressType type, bool includeDetails)
    {
        //Return null if ADDRESSFAM is Ipv6 but Os does not support it
        if (type == AddressType.IPv6 && !Socket.OSSupportsIPv6)
        {
            return null;
        }

        List<string> output = new List<string>();

        foreach (NetworkInterface item in NetworkInterface.GetAllNetworkInterfaces())
        {

#if UNITY_EDITOR_WIN || UNITY_STANDALONE_WIN || UNITY_EDITOR_OSX || UNITY_STANDALONE_OSX || UNITY_IOS
            NetworkInterfaceType _type1 = NetworkInterfaceType.Wireless80211;
            NetworkInterfaceType _type2 = NetworkInterfaceType.Ethernet;

            bool isCandidate = (item.NetworkInterfaceType == _type1 || item.NetworkInterfaceType == _type2);

#if UNITY_EDITOR_WIN || UNITY_STANDALONE_WIN
            // as of MacOS (10.13) and iOS (12.1), OperationalStatus seems to be always "Unknown".
            isCandidate = isCandidate && item.OperationalStatus == OperationalStatus.Up;
#endif

            if (isCandidate)
#endif
            {
                foreach (UnicastIPAddressInformation ip in item.GetIPProperties().UnicastAddresses)
                {
                    //IPv4
                    if (type == AddressType.IPv4)
                    {
                        if (ip.Address.AddressFamily == AddressFamily.InterNetwork)
                        {
                            string s = ip.Address.ToString();
                            if (includeDetails)
                            {
                                s += "  " + item.Description.PadLeft(6) + item.NetworkInterfaceType.ToString().PadLeft(10);
                            }
                            output.Add(s);
                        }
                    }

                    //IPv6
                    else if (type == AddressType.IPv6)
                    {
                        if (ip.Address.AddressFamily == AddressFamily.InterNetworkV6)
                        {
                            output.Add(ip.Address.ToString());
                        }
                    }
                }
            }
        }
        return output;
    }
#endif
}