wsdd

wsdd implements a Web Service Discovery host daemon. This enables (Samba) hosts, like your local NAS device, to be found by Web Service Discovery Clients like Windows.

Purpose

Since NetBIOS discovery is not supported by Windows anymore, wsdd makes hosts to appear in Windows again using the Web Service Discovery method. This is beneficial for devices running Samba, like NAS or file sharing servers on your local network.

Background

With Windows 10 version 1511, support for SMBv1 and thus NetBIOS device discovery was disabled by default. Depending on the actual edition, later versions of Windows starting from version 1709 ("Fall Creators Update") do not allow the installation of the SMBv1 client anymore. This causes hosts running Samba not to be listed in the Explorer's "Network (Neighborhood)" views. While there is no connectivity problem and Samba will still run fine, users might want to have their Samba hosts to be listed by Windows automatically.

You may ask: What about Samba itself, shouldn't this functionality be included in Samba!? Yes, maybe. However, using Samba as file sharing service is still possible even if the host running Samba is not listed in the Network Neighborhood. You can still connect using the host name (given that name resolution works) or IP address. So you can have network drives and use shared folders as well. In addition, there is a patch lurking around in the Samba bug tracker since 2015. So it may happen that this feature gets integrated into Samba at some time in the future.

Requirements

wsdd requires Python 3 only. It runs on Linux and FreeBSD. Other Unixes, such as OpenBSD or NetBSD, might work as well but were not tested.

Although Samba is not strictly required by wsdd itself, it makes sense to run wsdd only on hosts with a running Samba daemon. Note that the OpenRC/Gentoo init script depends on the Samba service.

Installation and Usage

No installation steps are required. Just place the wsdd.py file anywhere you want to, rename it to wsdd, and run it from there. The init scripts/unit files assume that wsdd is installed under /usr/bin/wsdd or /usr/local/bin/wsdd in case of FreeBSD. There are no configuration files. No special privileges are required to run wsdd, so it is advisable to run the service as an unprivileged user such as nobody.

The etc directory of the repo contains sample configuration files for different init(1) systems, namely FreeBSD's rc.d, Gentoo's openrc, and systemd which is used in most contemporary Linux distros. Those files may be used as templates for their actual usage. They are likely to require adjustments to the actual distribution/installation where they are to be used.

Firewall Setup

Both incoming and outgoing multicast traffic on port 3702 must be allowed. For IPv4, the multicast address is 239.255.255.250, for IPv6 the link local SSDP multicast address (fe02::c) is used.

Incoming TCP traffic (and related outgoing traffic) on port 5357 must be allowed.

Options

• -i INTERFACE, --interface INTERFACE

  Specify on which interfaces wsdd will be listening on. If no interfaces are specified, all interfaces are used. The loop-back interface is never used, even when it was explicitly specified. For interfaces with IPv6 addresses, only link-local addresses will be used for announcing the host on the network. This option can be provided multiple times in order to use more than interface (but no all).

• -H HOPLIMIT, --hoplimit HOPLIMIT

  Set the hop limit for multicast packets. The default is 1 which should prevent packets from leaving the local network segment.

• -U UUID, --uuid UUID

  The WSD specification requires a device to have a unique address that is stable across reboots or changes in networks. In the context of the standard, it is assumed that this is something like a serial number. wsdd uses the UUID version 5 with the DNS namespace and the host name of the local machine as inputs. Thus, the host name should be stable and not be modified, e.g. by DHCP. However, if you want wsdd to use a specific UUID you can use this option.

• -d DOMAIN, --domain DOMAIN

  Assume that the host running wsdd joined an ADS domain. This will make wsdd report the host being a domain member. It disables workgroup membership reporting. The (provided) hostname is automatically converted to lower case. Use the -p option to change this behavior.

• -n HOSTNAME, --hostname HOSTNAME

  Override the host name wsdd uses during discovery. By default the machine's host name is used (look at hostname(1)). Only the host name part of a possible FQDN will be used in the default case.

• -w WORKGROUP, --workgroup WORKGROUP

  By default wsdd reports the host is a member of a workgroup rather than a domain (use the -d/--domain option to override this). With -w/--workgroup the default workgroup name can be changed. The default work group name is WORKGROUP. The (provided) hostname is automatically converted to upper case. Use the -p option to change this behavior.

• -t, --nohttp

  Do not service http requests of the WSD protocol. This option is intended for debugging purposes where another process may handle the Get messages.

• -c DIRECTORY, --chroot DIRECTORY

  Chroot into a separate directory to prevent access to other directories of the system. This increases security in case of a vulnerability in wsdd. Consider setting the user and group under which wssd is running by using the -u option.

• -u USER[:GROUP], --user USER[:GROUP]

  Change user (and group) when running before handling network packets. Together with -c this option can be used to increase security if the execution environment, like the init system, cannot ensure this in another way.

• -v, --verbose

  Additively increase verbosity of the log output. A single occurrence of -v/--verbose sets the log level to INFO. More -v options set the log level to DEBUG.

• -s, --shortlog

  Use a shorter logging format that only includes the level and message. This is useful in cases where the logging mechanism, like systemd on Linux, automatically prepend a date and process name plus ID to the log message.

• -p, --preserve-case

  Preserve the hostname as it is. Without this option, the hostname is converted as follows. For workgroup environments (see -w) the hostname is made upper case by default. Vice versa it is made lower case for usage in domains (see -d).

• -4, --ipv4only (see below)

• -6, --ipv6only

  Restrict to the given address family. If both options are specified no addreses will be available and wsdd will exit.

Example Usage

• handle traffic on eth0 only, but only with IPv6 addresses

  wsdd -i eth0 -6

  or

  wsdd --interface eth0 --ipv6only

• set the Workgroup according to smb.conf and be verbose

  SMB_GROUP=$(grep -i '^\s*workgroup\s*=' smb.conf | cut -f2 -d= | tr -d '[:blank:]')

  wsdd -v -w $SMB_GROUP

Technical Description

(Read the source for more details)

For each specified (or all) network interfaces, except for loopback, an UDP multicast socket for message reception, an UDP send socket for replying messages using unicast, and a listening TCP socket is created. This is done for both the IPv4 and the IPv6 address family if not configured otherwise by the command line arguments (see above). Upon startup a Hello message is sent. When wsdd terminates due to a SIGTERM signal or keyboard interrupt, a graceful shutdown is performed by sending a Bye message. I/O multiplexing is used to handle network traffic of the different sockets within a single process.

Known Issues

Security

wsdd does not implement any security feature, e.g. by using TLS for the http service. This is because wsdd's intended usage is within private, i.e. home, LANs. The Hello message contains the hosts transport address, i.e. the IP address which speeds up discovery (avoids Resolve message).

In order to increase the security, use the capabilities of the init system or consider the -u and -c options.

Using only IPv6 on FreeBSD

If wsdd is running on FreeBSD using IPv6 only, the host running wsdd may not be reliably discovered. The reason appears to be that Windows is not always able to connect to the HTTP service for unknown reasons. As a workaround, run wsdd with IPv4 only.

Usage with NATs

Do not use wssd on interfaces that are affected by NAT. According to the standard, the ResolveMatch messages emitted by wsdd, contain the IP address ("transport address" in standard parlance) of the interface(s) the application has been bound to into. When such messages are retrieved by a client (Windows hosts, e.g.) they are unlikely to be able to connect to the provided address which has been subject to NAT. To avoid this issue, use the -i/--interface option to bind wsdd to interfaces not affected by NAT.

Tunnel/Bridge Interface

If tunnel/bridge interfaces like those created by OpenVPN or Docker exist, they may interfere with wsdd if executed without providing an interface that it should bind to (so it binds to all). In such cases, the wsdd hosts appears after wsdd has been started but it disappears when an update of the Network view in Windows Explorer is forced, either by refreshing the view or by a reboot of the Windows machine. To solve this issue, the interface that is connected to the network on which the host should be announced needs to be specified with the -i/--interface option. This prevents the usage of the tunnel/bridge interfaces.

Background: Tunnel/bridge interfaces may cause Resolve requests from Windows hosts to be delivered to wsdd multiple times,´i.e. duplicates of such request are created. If wsdd receives such a request first from a tunnel/bridge it uses the transport address (IP address) of that interface and sends the response via unicast. Further duplicates are not processed due to the duplicate message detection which is based on message UUIDs. The Windows host which receives the response appears to detect a mismatch between the transport address in the ResolveMatch message (which is the tunnel/bridge address) and the IP of the sending host/interface (LAN IP, e.g.). Subsequently, the wsdd host is ignored by Windows.

Contributing

Contributions are welcome. Please ensure PEP8 compliance when submitting patches or pull requests.

Licence

The code is licensed under the MIT license.

Acknowledgements

Thanks to Jose M. Prieto and his colleague Tobias Waldvogel who wrote the mentioned patch for Samba to provide WSD and LLMNR support. A look at their patch set made cross-checking the WSD messages easier.

References and Further Reading

Technical Specification

• Web Services Dynamic Discovery

• SOAP-over-UDP (used during multicast)

• MSDN Documentation on Publication Services Data Structure

• MSDN on Windows WSD Compliance

• ...and the standards referenced within the above.

Documentation and Discussion on Windows/WSD

• Microsoft help entry on SMBv1 is not installed by default in Windows 10 Fall Creators Update and Windows Server, version 1709

• Samba WSD and LLMNR support (Samba Bug #11473)

• Discussion at tenforums.com about missing hosts in network Note: Solutions suggest to go back to SMBv1 protocol which is deprecated! Do not follow this advice.

• Discussion in Synology Community Forum

Other stuff

• Meanwhile, there is a C implementation of a WSD daemon, named wsdd2. This one also includes LLMNR which wsdd lacks. However, LLMNR may not be required depending on the actual network/name resolution setup.

• OpenWRT includes the above C implementation. So OpenWRT users are unlikely to need an installation of wsdd.

• FreeNAS appears to have wsdd included in the distribution.