[Freeciv-Dev] Re: (PR#6707) Announce server on LAN

["Raimar Falke" <i-freeciv-lists@xxxxxxxxxxxxx>]

On Wed, Nov 05, 2003 at 06:02:02AM -0800, Todd Goodman wrote:
> * Raimar Falke <i-freeciv-lists@xxxxxxxxxxxxx> [031105 07:04]:
> > On Mon, Nov 03, 2003 at 11:05:37AM -0800, Todd Goodman wrote:
> > > * Raimar Falke <i-freeciv-lists@xxxxxxxxxxxxx> [031103 11:30]:
> > > > In addition the URL states:
> > > > 
> > > >    In any case, range 224.0.0.0 through 224.0.0.255 is reserved for
> > > >    local purposes (as administrative and maintenance tasks) and
> > > >    datagrams destined to them are never forwarded by multicast
> > > >    routers.
> > > > 
> > > > So if we choose 224.0.0.1 we know that all hosts are on this group AND
> > > > we know that the TTL is irrelevant since the packets are routed.
> > > > 
> > > > The only problem I see is that the server is behind a router. So how
> > > > do you define LAN?
> > > > 
> > > > If all this is correct I'm favoring as the default a scan in 224.0.0.1
> > > > with no special TTL and (optionally if you want to code it) "an export
> > > > mode" where you can input a special multicast group and optionally a
> > > > TTL.
> > > 
> > > But why would you send all hosts on the local network Freeciv specific
> > > packets?
> > 
> > Because it is multicast.
> 
> But it isn't broadcast.
> 
> The whole point of multicast is to send to a subset of addresses on the
> Ethernet without resorting to broadcasting.
> 
> The all hosts address is mainly so that routers can send packets that all
> hosts would like to receive (supposedly all hosts would want to receive
> an indication that they can send traffic off the local network via that
> router.)

I want to minimize the requirements for freeciv. This means that it is
bad that a user have to run a special program before he can play
freeciv or that the user has to install extra software or (the worst)
have to recompile his kernel/OS.

Also portabiltiy is important. Searching for SIOCADDMULTI and "win32"
or "winsock" didn't reveal
anything. http://msdn.microsoft.com/library/en-us/winsock/winsock/wsaioctl_2.asp
mentions SIO_RCVALL_MCAST and adds:

   Setting this ioctl requires Administrator privilege on the local
   computer. SIO_RCVALL_MCAST is available only in Windows 2000 and
   later versions of Windows.

It doesn't looks to me like there is an easy way to add this feature
for win32 systems.

The current patch doesn't add new requirements and may just not work
if your OS don't support multicast or your switch drop these packets
or any other problem happens. While I would prefer a solution where
you can at compile or runtime detect that there is multicast enable
the patch is ok.

Speaking of which: if I ping 224.0.0.1 I should get a reply from
myself?! Yes/no? If yes we can use this to test if the software
supports multicast at all.

> > > That seems like a good way to get administrators mad at Freeciv and any
> > > users running it.
> > 
> > Not from 1 byte packets.
> 
> You know different administrators than I do.  :-)

You mean that the administrators really succeeded in killing all p2p
traffic? Here they had to use bandwidth limits.

        Raimar

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