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  {Extensions in Samba - CIFS'98\hspace{\fill}\rightmark \hspace{\fill}\thepage}{}%
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\begin{document}
\LARGE


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\newpage
\begin{slide}
\heading{Samba and SMB/CIFS}

The CIFS/SMB protocol has been notorious for each implementation doing
their own little extensions to add features or work around problems in
other implementations. Samba is no exception.

In this talk I'll describe some of the more interesting extensions
that we have put into Samba. Although other implementors don't need to
know about these extensions to inter-operate with Samba I'm hoping that
airing these in public will give some useful ideas for other
implementors and promote discussion.

\end{slide}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newpage
\begin{slide}
\heading{WINS and *1B}

Cross-subnet browsing has always been difficult with SMB. It can be
made to work with the protocols as they exist in the spec but not
without a lot of trouble and only if your network layout is ``just
right''.

After looking at this we found that the core piece of missing
technology is some way for a host to ask the WINS server for a
complete list of Domain Master Browsers that it knows about. Given
that information it is easy to construct enterprise wide browse lists.

We solved this by extending the Samba WINS server to accept name
queries queries for the name *1B. The query will return the current
list of known Domain Master Browser IP addresses.
\end{slide}

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\newpage
\begin{slide}
\heading{Browse Synchronization}

To use the *1B feature we modified our DMB implementation to
periodically send *1B queries to the WINS server (if present). If
the query is successful then a node status request is sent to any of
the resulting IPs which are unknown to the DMB. The node status
request is used to determine the workgroup name. Resulting workgroups
are scheduled for browse synchronization via the normal mechanisms.

\end{slide}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newpage
\begin{slide}
\heading{Inter-DMB synchronization}

Our *1B browse synchronization solves the cross-subnet browsing
issue when all DMBs are using the same WINS server, but does nothing
to help the case where some DMBs use a different WINS server or use
broadcast registration.

To solve this problem we added inter-DMB synchronization. Each Samba
DMB will perform a workgroup browse sync with all currently known
DMBs by choosing a random DMB to sync with at regular intervals. The
frequency of these sync operations is fixed, regardless of the number
of DMBs, thus preventing a $N^2$ explosion of network traffic.

These sync operations allow a Samba DMB to build a much more complete
list of workgroups. The disadvantage is that ``dead'' workgroups can
survive for long after they have no members. We are thinking about a
solution to that problem, which is caused by lack of TTL information
if the NetServerEnum response.

\end{slide}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newpage
\begin{slide}
\heading{Remote announce}

When the above mechanisms fail, such as in very disjoint networks
without a WINS server, it is sometimes useful to tell Samba to send
host announcements to a remote subnet where they will be picked up by
the local master browser. You can do this using a ``remote announce''
option.

This option allows you to force the appearance of a server in any
workgroup listing you like as long as you know the broadcast address
of the remote network. Even over an international link.
\end{slide}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newpage
\begin{slide}
\heading{Netbios aliases}

Samba can announce and register itself as any number of simultaneous
netbios names on the network. This can be useful when the server has
multiple roles which you may want to split onto separate machines at a
later date. 

Associated with each name can be a Samba config file, so you can
configure each of the names to behave quite differently. For example
one may be a user level security file server and another might be a
share level security print server.

\end{slide}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newpage
\begin{slide}
\heading{Encryption conversion}

A constant headache for Unix SMB server implementations is the
handling of the encrypted SMB password database and its
synchronization with the standard unix password systems. 

To try to reduce the pain a little Samba can auto-add users to the
encrypted database as they login. This allows you to convert from
non-encrypted to encrypted with a minimum of fuss.

\end{slide}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newpage
\begin{slide}
\heading{sync options}

Windows programmers don't seem to know the difference between sync()
and flush(). We see quite a few programs (Explorer being one of them!)
using O\_SYNC when opening files in a quite inappropriate manner. This
has an enormous performance penalty.

For this reason we give the administrator the option of ignoring sync
requests (this can be set on a per share basis).

\end{slide}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newpage
\begin{slide}
\heading{smbwrapper}

For Samba 2.0 we have implemented a library of posix-like filesystem
functions that can be preloaded by a unix loader, allowing existing
unix binaries to see a virtual SMB filesystem and network
neighborhood. 

This provides a SMB client filesystem on a wide range of Unix flavors
which finally allows unix systems to become true members of a SMB
workgroup. 

The system (called smbwrapper) also shows printer shares as
directories, with printing via cp, print queue listing via ls and
print queue deletion via rm.
\end{slide}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newpage
\begin{slide}
\heading{SSL}

Samba 2.0 has SSL support in both the client and server (contributed
by Christian Starkjohann). This allows SMB sessions to be established
over an underlying secure transport, giving a fully encrypted network
filesystem.

This is particularly useful in conjunction with smbwrapper.

\end{slide}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newpage
\begin{slide}
\heading{summary}

Samba tries to be as compliant as possible with the SMB and CIFS
specifications as they are currently known, as well as the
implementation quirks of WinNT and Win95. Beyond that we have also
implemented a number of extensions that make Samba more useful without
breaking access from clients that don't have the extensions.

I hope that the description of some of these extensions will give
ideas to other SMB implementors and promote discussion of the
protocol.

Questions?
\end{slide}


\end{document}
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