[Opensim-users] NAT & Corporate Firewall

Tue Apr 5 00:23:41 UTC 2011

On 04/04/11 17:22, Fleep Tuque wrote:
> Indeed, thanks to everyone for the help.  We're investigating the possibility of a "virtual NIC" sitting outside the
> campus firewall since there doesn't appear to be any easier way to resolve the issue, but I'm not sure yet how that will
> work or if we'll get approval from the security dragons.  ;)
>
> Out of curiosity, is there a reason why the DNS resolution is done at the server for the UDP region handshake instead of
> sending the hostname to the client as seems to be done with the TCP traffic?   I'm guessing it can't be an easy thing to
> change or someone probably would have done by now..

I'm not entirely sure - sometimes the reasons for these things get lost in the mists of time (often when people don't 
document!).  If nobody knows for sure then some experimentation might be in order.

>
> Thanks again though, it's good to know how that bit actually works!

Thanks for the update and the contributions of everybody on this thread.  I've clarified the "Internal IP address" line 
at http://opensimulator.org/wiki/Configuration#Running_OpenSim_for_the_first_time

>
> Sincerely,
>
> - Chris/Fleep
>
>
> Chris M. Collins (SL: Fleep Tuque)
> Project Manager, UC Second Life
> Second Life Ambassador, Ohio Learning Network
> UCit Instructional & Research Computing
> University of Cincinnati
> 406E Zimmer Hall
> PO Box 210088
> Cincinnati, OH 45221-0088
> (513)556-3018
> chris.collins at uc.edu <mailto:chris.collins at uc.edu>
>
> UC Second Life: http://homepages.uc.edu/secondlife
> OLN Second Life: http://www.oln.org/emerging_technologies/emtech.php
>
>
>
> On Fri, Apr 1, 2011 at 9:40 PM, Justin Clark-Casey <jjustincc at googlemail.com <mailto:jjustincc at googlemail.com>> wrote:
>
>     Thanks for the info Simon, that's cleared that up for me.  And thanks to the others contributing to this thread.
>
>     I think that a utility to test a connection and provide an explicit diagnosis (rather than the clues provided by the
>     client just hanging in various places) would be rather nice to have.
>
>
>     On 01/04/11 12:59, Simon Slavin wrote:
>
>
>         On 1 Apr 2011, at 12:43am, Justin Clark-Casey wrote:
>
>             Some people on Stack Overflow think that IPAddress.Any means listen on all NICs
>             (http://stackoverflow.com/questions/1777629/how-to-listen-on-multiple-ip-addresses).  But my reading of the
>             MS SDK reference above means that it only binds to one.  Anybody able to comment on this?
>
>
>         Stack Overflow is right.  My reading of that SDK page is that it's wrong, and should be corrected, but other MS
>         documentation is clearer on what '::Any' means, for example
>
>         http://msdn.microsoft.com/en-us/library/system.net.ipaddress.any.aspx
>
>         Returning to the standards, IP address 0.0.0.0 is reserved for specific purposes for both sending and receiving.
>           It's called the 'anonymous' address (for historical reasons) or the 'broadcast' address (for current reasons).
>
>         If a computer SENDS a packet to 0.0.0.0 then it is multibroadcasting: sending one message to every computer that
>         can hear it.  This is done most often to announce the (un)availability of a service, for instance that a printer
>         service has come online.  Sending to address 0.0.0.0 is done by, for example, DHCP and zeroconf (what Apple
>         calls 'Bonjour').  Things like routers are usually set up to drop packets SENT to 0.0.0.0 so that you don't
>         announce to the entire world what address your printer can be found on.
>
>         When a computer LISTENS to the network interface bound to 0.0.0.0 then it is telling its TCP stack that it
>         doesn't care which network interface a message comes in on, it wants it anyway.  Almost every Internet
>         application does this, especially now many have both Ethernet sockets and WiFi capabilities: an app doesn't care
>         what its user is using right now, it just wants to 'use the internet'.  Under normal circumstances the only
>         programs which /don't/ listen on 0.0.0.0 are techie programs like network utilities, or a web server on a
>         gateway computer which needs to present a web site to internal users and make sure it isn't available to
>         external users.
>
>         I tried to find an RFC to point to as reference but nothing seems to spell this out.  The nearest thing i could
>         find was RFC950.
>
>         Simon.
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>
>
>     --
>     Justin Clark-Casey (justincc)
>     http://justincc.org/blog
>     http://twitter.com/justincc
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-- 
Justin Clark-Casey (justincc)
http://justincc.org/blog
http://twitter.com/justincc