Hi Craig,
Sorry for bothering you with another question of
"getting IP of remote client" !
0
>From my understanding, DNS is also
a "push technology"(because DNS also use UDP ?), so if a user
is behind firewall, how can his/her DNS server reply to him/her
if this DNS server is in "the other side:-) " of the firewall?
1
I guess DNS server also need to know the "real IP" of the client,
so DNS server can send a UDP package to its client who send a
"domain name" to this DNS server
2
from a book about firewall, the default setting of some firewalls will
"open" UDP port 53(for DNS), so I guess:
[1] if a user is behind the firewall, then his/her "UDP package
which include the quering to his/her DNS server" will be
sent to firewall first
[2] then firewall will replace the "source IP" with one of the IP
of this firewall, and re-send it to DNS server
[3] So the replying of DNS server will be sent to firewall first
[4] then: firewall will:
a broadcast this UDP package to all clients with UDP
multicast
b or ... (I don't know :-) )
Is the above right?
Thanks for your time in advance!
Bo
Sept.17,2000
"Craig R. McClanahan" wrote:
> Bo Xu wrote:
>
> > Hi Craig,
> >
> > Would you please tell me if :
> >
> > 0
> > I have a TCP server
> >
> > 1
> > a I have a applet which connect to my TCP server
> > b I have already enabled some necessary "Privileges" for Netscape and IE
> >
> > 2
> > Now in my TCP server, with :
> >
> > "s.getInetAddress().getHostAddress()" (s is a Socket)
> >
> > a Can I always get the "real :-)" IP of client if the client computer has a
>public IP
> > in the following cases:
> > client is behide a firewall
>
> You will get a "real" IP address, but it will be the address of the firewall or
>gateway (depending on how that particular company has configured things), not the IP
>address of the PC itself.
>
> >
> > client uses a proxy server ( I don't know if there is "proxy server" for
>TCP socket? )
>
> For HTTP, proxy servers are quite common, and it is easy to configure your browser
>to use one.
>
> As in the previous case, your server will get the IP address of the proxy server,
>not of the client PC itself.
>
> > ...
> >
> > b What will I get if client computer doesn't has a public IP or doesn't has
>a IP
> > in the following cases metioned in your email :
> > >... Indeed, the PC itself may not even *have* a real IP address -- it
>might
> > >be using the reserved Intranet >address >ranges (with the
> > >gateway providing address translation), or it might even be running a
>non-IP
> > >protocol internally (with the gateway providing protocol translation as
>well) ...
> >
>
> Same as the above -- you will receive a real IP address of whatever
>Internet-accessible device is responsible for managing traffic for this user
>(gateway, firewall, proxy server, whatever).
>
> >
> > 3
> > Because now I am developing a audio/video live software with JMF
> > (Java Media Framwork), and JMF uses RTP/UDP to send stream,
> > so I need to know the "real" IP of client if it has . I have tried with servlet,
> > and now I try to use TCP socket.
> >
> > If this email is "off-topic", I am sorry for that !
> >
>
> Only this particular question :-). I don't know the details, but I suspect you're
>going to have problems with trying to broadcast UDP packets across the Internet to
>clients behind firewalls. Remember all the hype about
> "push" technology a couple of years ago. If you look inside, most of the
>implementations actually used a "pull" approach, with the client polling the server
>for updates -- for exactly these types of reasons.
>
> >
> > Thanks in advance !
> >
> > Bo
> > Sept.11,2000
> >
>
> Craig
>
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