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To: <cipe-l,AT,inka,DOT,de>
Subject: RE: Broadcast and CIPE-Win32
From: "Mark Smith" <mark.smith,AT,avcosystems,DOT,co,DOT,uk>
Date: Tue, 15 Jul 2003 14:57:26 +0100
Importance: Normal
In-reply-to: <3F1403AD.70207@free.fr>

Olivier Guyotot wrote:

> What exactly is bridging and how is it related to broadcasts?

Bridging is the act of passing all traffic from one side of the tunnel
transparently through to the other, where both sides usually have the same
IP address range.  The net effect is that it appears that both ends of the
tunnel are connected together directly.  However, in it's normal
configuration, CIPE acts instead as a pair of network adapters connecting to
two different IP address ranges.

> If broadcasts do work, does it mean I should be able to play
> LAN games
> without further configuration? and if so, then what is wrong in my
> current setup? (I can ping each peer, play games if I specify the IP
> address of the server, but cannot "automatically discover
> created games).

What quite often happens here is that your local computer is sending
broadcast packets out to the local ethernet segment using the local
broadcast address.  These don't get forwarded over the tunnel because it has
different address ranges.  Consequently, the machine on the other side of
the tunnel, with a different address, address range and broadcast address,
does not see the original broadcast packet.  Even if it was forwarded
through the tunnel, the address ranges would not be the same and the other
machine would ignore the packet

If you are in control of all of the machines on both ends, you may be able
to set a broadcast address that encompasses both ends, assuming they both
lie within a compatible range.  They will still need to be different enough
to allow routing to know where to send the packets, but this may just get
around your problem.

For example, one end might be, the other might be, the netmask for all machines on both ends would need to be, the broadcast address would need to be  This
actually constructs a single /23 network.  You should still be able to route
traffic between the two ends over CIPE, yet should in theory also pass
broadcast traffic in a manner that the machines would accept.

I haven't tried this.  YMMV.

Mark Smith - Avco Systems Ltd
email: mark.smith,AT,avcosystems,DOT,co,DOT,uk
Tel: +44 (0)1784 430996 Fax: +44 (0)1784 431078

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