Hi Tiru,
The problem with NAT for protocols like FTP can be solved by using PCP
(http://tools.ietf.org/html/rfc6887).
Sure it can and even should. But the tcpinc charter states that the
solution must not require modifying existing applications, and PCP
is not widely supported nowdays, AFAIK.
Valery.
-Tiru
> Hi Yoav,
>
> > Hi Brian, Valery
> >
> > FTP comes in two varieties: active and passive.
>
> True.
>
> > There is no issue in passive mode FTP with tcpinc, as the client opens
> > all the connections.
>
> Not quite. For an active mode there is an issue if client is behind NAT.
> For a passive mode there is an issue if server is behind NAT.
> (Well, it's true that in passive mode client opens all connections, but
> server
> still indicates the address and port the client should connect to for
> data
> transfer in the control connection, and if the server is behind NAT then
> these
> values need to be adjusted by NAT). I admit that the situation when
> server is
> behind NAT is more rare, than when client is behind NAT, but it is not
> uncommon. Consider home network connected to the Internet via ISP's NAT
> with FTP server installed that is accessible from the internet.
> Nowdays this setup is supported by most "off shelf" routers and there
> are
> plenty of free dynamic DNS services that solve the problem of
> non-staticness
> of IP address of the server.
>
> > For active, there is an issue with using tcpinc on the control
> > connection, but no issue for the data connection.
>
> True. But note. that control connection transmits user name and
> password,
> that may be of interest for attacker (unless it is anonymous ftp).
>
> > AFAIK (and according to Wikipedia) browsers implement passive FTP so
> > clicking on ftp:// links will work with tcpinc.
>
> Agree. But there are many standalone clients that don't support passive
> mode or don't use it by default. Moreover, some applications use ftp
> internally (for example to get updates) and user often has no means to
> change the way they do it.
>
> Regards,
> Valery.
>
> > Yoav
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