RE: Hub Lessons Learned

[mcs101main@xxxxxxx]

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I tried 0.0.0.0 for the RemoteHost of the Winsock control under W2K and it
was not received by a second Winsock control at a different port on the
same application.  This is the same as if I used 255.255.255.255.  If I use
127.0.0.1 for the RemoteHost then the second Winsock control receives the
message.  The 255.255.255.255 was tried on two computers.  The 0.0.0.0 was
tried on one.

It is true that the VPN may not be the culprit, but it was a common element
among the three computers on which I did my testing.  The two with eacfilt
drivers for the VPN had message duplicates and the one that did not have
this saw only single messages.  Duplicates occurred on  a Dell D600 laptop
under W2K using Broadcom 570x controller.  It also occurred on MSI
motherboard with integrated Intel NIC under W2K.  Duplication did not occur
under XP with a Linksys PCI card in a ECS motherboard.  W2K was another
common element between the two which have duplicates, but I know many are
using W2K without any reported duplication problems.


-------------- Original message from "Patrick Lidstone (Personal
e-mail)" : --------------


-----Original Message-----
From: mcs101main@xxxxxxx [mailto:mcs101main@xxxxxxx]
Sent: 25 October 2004 15:40
To: xAP_developer@xxxxxxx
Subject: [xAP_developer] Hub Lessons Learned


In working with a hub implementation on various PCs there are a few lessons
that I have learned and will share for others that have hub developement
interest.

1.  It is possible that a PC with LAN card(s) will only show 127.0.0.1 as
the only available network.  In my case it is a laptop when disconnected
from both the wired and wireless networks.  This means that a hub should
route traffic on this interface accordingly.  I have found that a
255.255.255.255 broadcast IP does not function on 127.0.0.1 and that the
target must explicitly be 127.0.0.1.  Note that message viewers also should
be cognizant of a 127.0.0.1-only network as well.

Have you tried 0.0.0.0 ? Broadcast can definitely be made to work on just
the loopback interface.

2. It appears that a VPN connection is treated as a virtual interface that
is mapped into the same physical interface as the primary LAN.  The fallout
of this is that the interface will report 2 message reception events for
each message received.  It does not matter if the VPN connection is alive
or not.  Its existance is what creates the problem.  There are also
confirmed bugs in some Microsoft Winsock implementations in which two
events are generated on a message reception.  I handled the VPN situation
by not forwarding any duplicate reception within a 100 millisecond window.

I have a variety of VPN clients installed, under Win2K, and I've never seen
this behaviour. I'm not saying it can't happen, just that I haven't seen
it... We could add an auto-incrementing sequence number to messages at
source if this turns out to be a widespread problem.

I suspect that other computers will exhibit unanticipated behaviors and
each needs to be dealt with on a case-by-case basis to understand what a
hub must do to accomdate.

Patrick