Discussion:
[EE] Passive Ethernet Hub?
Harold Hallikainen
2018-08-30 04:50:24 UTC
Permalink
I have a hub here that I use all the time with Wire Shark. Sometimes I
need to help someone debug something in the field, and they don't have a
hub, and they are getting hard to come by.

Since 10/100 Ethernet uses two pair, one for transmit, and one for
receive, it SEEMS like it should be possible to make a resistive hub where
each transmit pair drives the receive pairs of the other two ports (total
of 3 ports). I've done similar resistive networks for audio splitting
while maintaining impedances. But, I haven't figured out whether this
would work or what the resistor values would be. I did find a passive hub
using a bunch of diodes, but it seems like resistors should work. I also
see Ethernet taps where there are four ports. Data going one way between
the other two ports shows up on one of the monitor ports while data going
the other way shows up on the other monitor port. This requires two
Ethernet ports on the computer running WireShark, which is a pain.

So, any ideas on this? Is it possible to use resistive splitters to make a
passive hub?

Thanks!

Harold
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Isaac M. Bavaresco
2018-08-30 09:37:09 UTC
Permalink
Use Cain&Abel (or other hackering software) to turn a switch into a hub by
ARP Spoofing/routing table overflow.

Em qui, 30 de ago de 2018 02:46, Harold Hallikainen <
Post by Harold Hallikainen
I have a hub here that I use all the time with Wire Shark. Sometimes I
need to help someone debug something in the field, and they don't have a
hub, and they are getting hard to come by.
Since 10/100 Ethernet uses two pair, one for transmit, and one for
receive, it SEEMS like it should be possible to make a resistive hub where
each transmit pair drives the receive pairs of the other two ports (total
of 3 ports). I've done similar resistive networks for audio splitting
while maintaining impedances. But, I haven't figured out whether this
would work or what the resistor values would be. I did find a passive hub
using a bunch of diodes, but it seems like resistors should work. I also
see Ethernet taps where there are four ports. Data going one way between
the other two ports shows up on one of the monitor ports while data going
the other way shows up on the other monitor port. This requires two
Ethernet ports on the computer running WireShark, which is a pain.
So, any ideas on this? Is it possible to use resistive splitters to make a
passive hub?
Thanks!
Harold
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mike brown
2018-08-30 13:13:16 UTC
Permalink
This should do what you want.

https://www.amazon.com/Dualcomm-DCSW-1005-Powered-Ethernet-Mirroring/dp/B002BSF112
Post by Isaac M. Bavaresco
Use Cain&Abel (or other hackering software) to turn a switch into a hub by
ARP Spoofing/routing table overflow.
Em qui, 30 de ago de 2018 02:46, Harold Hallikainen <
Post by Harold Hallikainen
I have a hub here that I use all the time with Wire Shark. Sometimes I
need to help someone debug something in the field, and they don't have a
hub, and they are getting hard to come by.
Since 10/100 Ethernet uses two pair, one for transmit, and one for
receive, it SEEMS like it should be possible to make a resistive hub
where
Post by Harold Hallikainen
each transmit pair drives the receive pairs of the other two ports (total
of 3 ports). I've done similar resistive networks for audio splitting
while maintaining impedances. But, I haven't figured out whether this
would work or what the resistor values would be. I did find a passive hub
using a bunch of diodes, but it seems like resistors should work. I also
see Ethernet taps where there are four ports. Data going one way between
the other two ports shows up on one of the monitor ports while data going
the other way shows up on the other monitor port. This requires two
Ethernet ports on the computer running WireShark, which is a pain.
So, any ideas on this? Is it possible to use resistive splitters to make
a
Post by Harold Hallikainen
passive hub?
Thanks!
Harold
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DrSkip
2018-08-30 20:15:16 UTC
Permalink
This might even be better/cheaper:

https://www.amazon.com/Throwing-Original-Monitoring-Ethernet-Communication/dp/B077XY2TGD
Post by mike brown
This should do what you want.
https://www.amazon.com/Dualcomm-DCSW-1005-Powered-Ethernet-Mirroring/dp/B002BSF112
Post by Isaac M. Bavaresco
Use Cain&Abel (or other hackering software) to turn a switch into a hub by
ARP Spoofing/routing table overflow.
Em qui, 30 de ago de 2018 02:46, Harold Hallikainen <
Post by Harold Hallikainen
I have a hub here that I use all the time with Wire Shark. Sometimes I
need to help someone debug something in the field, and they don't have a
hub, and they are getting hard to come by.
Since 10/100 Ethernet uses two pair, one for transmit, and one for
receive, it SEEMS like it should be possible to make a resistive hub
where
Post by Harold Hallikainen
each transmit pair drives the receive pairs of the other two ports (total
of 3 ports). I've done similar resistive networks for audio splitting
while maintaining impedances. But, I haven't figured out whether this
would work or what the resistor values would be. I did find a passive hub
using a bunch of diodes, but it seems like resistors should work. I also
see Ethernet taps where there are four ports. Data going one way between
the other two ports shows up on one of the monitor ports while data going
the other way shows up on the other monitor port. This requires two
Ethernet ports on the computer running WireShark, which is a pain.
So, any ideas on this? Is it possible to use resistive splitters to make
a
Post by Harold Hallikainen
passive hub?
Thanks!
Harold
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Denny Esterline
2018-08-30 21:39:38 UTC
Permalink
Interesting. The simplicity of that suggests that somebody suitably
motivated might
create the same effect by mounting multiple jacks on a short length of
cable.
Post by DrSkip
https://www.amazon.com/Throwing-Original-Monitoring-Ethernet-Communication/dp/B077XY2TGD
Post by mike brown
This should do what you want.
https://www.amazon.com/Dualcomm-DCSW-1005-Powered-Ethernet-Mirroring/dp/B002BSF112
Post by mike brown
Post by Isaac M. Bavaresco
Use Cain&Abel (or other hackering software) to turn a switch into a hub
by
Post by mike brown
Post by Isaac M. Bavaresco
ARP Spoofing/routing table overflow.
Em qui, 30 de ago de 2018 02:46, Harold Hallikainen <
Post by Harold Hallikainen
I have a hub here that I use all the time with Wire Shark. Sometimes I
need to help someone debug something in the field, and they don't have
a
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
hub, and they are getting hard to come by.
Since 10/100 Ethernet uses two pair, one for transmit, and one for
receive, it SEEMS like it should be possible to make a resistive hub
where
Post by Harold Hallikainen
each transmit pair drives the receive pairs of the other two ports
(total
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
of 3 ports). I've done similar resistive networks for audio splitting
while maintaining impedances. But, I haven't figured out whether this
would work or what the resistor values would be. I did find a passive
hub
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
using a bunch of diodes, but it seems like resistors should work. I
also
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
see Ethernet taps where there are four ports. Data going one way
between
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
the other two ports shows up on one of the monitor ports while data
going
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
the other way shows up on the other monitor port. This requires two
Ethernet ports on the computer running WireShark, which is a pain.
So, any ideas on this? Is it possible to use resistive splitters to
make
Post by mike brown
Post by Isaac M. Bavaresco
a
Post by Harold Hallikainen
passive hub?
Thanks!
Harold
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Harold Hallikainen
2018-08-30 23:38:18 UTC
Permalink
Thanks to all! Following links to similar products, I found this:
https://www.amazon.com/Dualcomm-DCSW-1005-Powered-Ethernet-Mirroring/dp/B002BSF112
. I think I'll suggest customers buy this when debugging in the field.

The Throwing device is interesting, but it requires two Ethernet ports on
the system running Wireshark.

I've seen the diode circuit before, and it is REAL interesting! I wonder
if anyone is manufacturing that.

THANKS!

Harold
Post by DrSkip
https://www.amazon.com/Throwing-Original-Monitoring-Ethernet-Communication/dp/B077XY2TGD
Post by mike brown
This should do what you want.
https://www.amazon.com/Dualcomm-DCSW-1005-Powered-Ethernet-Mirroring/dp/B002BSF112
On Thu, Aug 30, 2018, 04:45 Isaac M. Bavaresco
Post by Isaac M. Bavaresco
Use Cain&Abel (or other hackering software) to turn a switch into a hub by
ARP Spoofing/routing table overflow.
Em qui, 30 de ago de 2018 02:46, Harold Hallikainen <
Post by Harold Hallikainen
I have a hub here that I use all the time with Wire Shark. Sometimes I
need to help someone debug something in the field, and they don't have a
hub, and they are getting hard to come by.
Since 10/100 Ethernet uses two pair, one for transmit, and one for
receive, it SEEMS like it should be possible to make a resistive hub
where
Post by Harold Hallikainen
each transmit pair drives the receive pairs of the other two ports (total
of 3 ports). I've done similar resistive networks for audio splitting
while maintaining impedances. But, I haven't figured out whether this
would work or what the resistor values would be. I did find a passive hub
using a bunch of diodes, but it seems like resistors should work. I also
see Ethernet taps where there are four ports. Data going one way between
the other two ports shows up on one of the monitor ports while data going
the other way shows up on the other monitor port. This requires two
Ethernet ports on the computer running WireShark, which is a pain.
So, any ideas on this? Is it possible to use resistive splitters to make
a
Post by Harold Hallikainen
passive hub?
Thanks!
Harold
--
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Allen Mulvey
2018-08-31 01:04:32 UTC
Permalink
You can do better than that. I have numerous old Cisco and
Dell switches that cost less than $30 and can do port
mirroring. (eg. Dell 2724) Check Ebay, etc.

Allen

-----Original Message-----
From: piclist-***@mit.edu
[mailto:piclist-***@mit.edu] On Behalf Of Harold
Hallikainen
Sent: Thursday, August 30, 2018 7:38 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Passive Ethernet Hub?

Thanks to all! Following links to similar products, I found
this:
https://www.amazon.com/Dualcomm-DCSW-1005-Powered-Ethernet-M
irroring/dp/B002BSF112
. I think I'll suggest customers buy this when debugging in
the field.

The Throwing device is interesting, but it requires two
Ethernet ports on
the system running Wireshark.

I've seen the diode circuit before, and it is REAL
interesting! I wonder
if anyone is manufacturing that.

THANKS!

Harold
https://www.amazon.com/Throwing-Original-Monitoring-Ethernet
-Communication/dp/B077XY2TGD
Post by Harold Hallikainen
Post by mike brown
This should do what you want.
https://www.amazon.com/Dualcomm-DCSW-1005-Powered-Ethernet-M
irroring/dp/B002BSF112
Post by Harold Hallikainen
Post by mike brown
On Thu, Aug 30, 2018, 04:45 Isaac M. Bavaresco
Post by Isaac M. Bavaresco
Use Cain&Abel (or other hackering software) to turn a
switch into a hub
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
by
ARP Spoofing/routing table overflow.
Em qui, 30 de ago de 2018 02:46, Harold Hallikainen <
Post by Harold Hallikainen
I have a hub here that I use all the time with Wire
Shark. Sometimes I
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
need to help someone debug something in the field, and
they don't have
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
a
hub, and they are getting hard to come by.
Since 10/100 Ethernet uses two pair, one for transmit,
and one for
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
receive, it SEEMS like it should be possible to make a
resistive hub
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
where
Post by Harold Hallikainen
each transmit pair drives the receive pairs of the
other two ports
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
(total
of 3 ports). I've done similar resistive networks for
audio splitting
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
while maintaining impedances. But, I haven't figured
out whether this
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
would work or what the resistor values would be. I did
find a passive
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
hub
using a bunch of diodes, but it seems like resistors
should work. I
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
also
see Ethernet taps where there are four ports. Data
going one way
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
between
the other two ports shows up on one of the monitor
ports while data
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
going
the other way shows up on the other monitor port. This
requires two
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
Ethernet ports on the computer running WireShark, which
is a pain.
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
So, any ideas on this? Is it possible to use resistive
splitters to
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
make
a
Post by Harold Hallikainen
passive hub?
Thanks!
Harold
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Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
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Harold Hallikainen
2018-08-31 01:53:19 UTC
Permalink
Thanks! I looked that up and then found similar device. It turns out that
there are a bunch of Netgear DS104s available. That happens to be what I
have here. I should probably just buy a bunch of them to loan out for
debugging Ethernet installations.

THANKS to everyone!

Harold
Post by Allen Mulvey
You can do better than that. I have numerous old Cisco and
Dell switches that cost less than $30 and can do port
mirroring. (eg. Dell 2724) Check Ebay, etc.
Allen
-----Original Message-----
Hallikainen
Sent: Thursday, August 30, 2018 7:38 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Passive Ethernet Hub?
Thanks to all! Following links to similar products, I found
https://www.amazon.com/Dualcomm-DCSW-1005-Powered-Ethernet-M
irroring/dp/B002BSF112
. I think I'll suggest customers buy this when debugging in
the field.
The Throwing device is interesting, but it requires two
Ethernet ports on
the system running Wireshark.
I've seen the diode circuit before, and it is REAL
interesting! I wonder
if anyone is manufacturing that.
THANKS!
Harold
https://www.amazon.com/Throwing-Original-Monitoring-Ethernet
-Communication/dp/B077XY2TGD
Post by Harold Hallikainen
Post by mike brown
This should do what you want.
https://www.amazon.com/Dualcomm-DCSW-1005-Powered-Ethernet-M
irroring/dp/B002BSF112
Post by Harold Hallikainen
Post by mike brown
On Thu, Aug 30, 2018, 04:45 Isaac M. Bavaresco
Post by Isaac M. Bavaresco
Use Cain&Abel (or other hackering software) to turn a
switch into a hub
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
by
ARP Spoofing/routing table overflow.
Em qui, 30 de ago de 2018 02:46, Harold Hallikainen <
Post by Harold Hallikainen
I have a hub here that I use all the time with Wire
Shark. Sometimes I
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
need to help someone debug something in the field, and
they don't have
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
a
hub, and they are getting hard to come by.
Since 10/100 Ethernet uses two pair, one for transmit,
and one for
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
receive, it SEEMS like it should be possible to make a
resistive hub
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
where
Post by Harold Hallikainen
each transmit pair drives the receive pairs of the
other two ports
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
(total
of 3 ports). I've done similar resistive networks for
audio splitting
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
while maintaining impedances. But, I haven't figured
out whether this
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
would work or what the resistor values would be. I did
find a passive
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
hub
using a bunch of diodes, but it seems like resistors
should work. I
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
also
see Ethernet taps where there are four ports. Data
going one way
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
between
the other two ports shows up on one of the monitor
ports while data
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
going
the other way shows up on the other monitor port. This
requires two
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
Ethernet ports on the computer running WireShark, which
is a pain.
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
So, any ideas on this? Is it possible to use resistive
splitters to
Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
make
a
Post by Harold Hallikainen
passive hub?
Thanks!
Harold
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Post by Harold Hallikainen
Post by mike brown
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
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RussellMc
2018-08-31 02:39:15 UTC
Permalink
Post by DrSkip
https://www.amazon.com/Throwing-Original-Monitoring-Ethernet-Communication/dp/B077XY2TGD
Darndest Shiraken I ever saw.
Wouldn't embed deeply with the jacks where they are.

_________

That's very obvious, in retrospect, if it works for your task.

The two PCs (etc) connect as usual and the monitor port connects only

as a receiver.

They say:

The Throwing Star LAN Tap is a passive Ethernet tap, requiring no power for
operation. There are active methods of tapping Ethernet connections (e.g.,
a mirror port on a switch), but none can beat passive taps for portability.
To the target network, the Throwing Star LAN Tap looks just like a section
of cable, but the wires in the cable extend to the monitoring ports in
addition to connecting one target port to the other.

The monitoring ports (J3 and J4) are receive-only; they connect to the
receive data lines on the monitoring station but do not connect to the
station's transmit lines. This makes it impossible for the monitoring
station to accidentally transmit data packets onto the target network.

The Throwing Star LAN Tap is designed to monitor 10BASET and 100BASETX
networks. It is not possible for an unpowered tap to perform monitoring of
1000BASET (Gigabit Ethernet) networks, so the Throwing Star LAN Tap
intentionally degrades the quality of 1000BASET target networks, forcing
them to negotiate a lower speed (typically 100BASETX) that can be passively
monitored. This is the purpose of the two capacitors (C1 and C2).


Like all passive LAN Taps, the Throwing Star LAN Tap degrades signal
quality to some extent. Except as described above for Gigabit networks,
this rarely causes problems on the target network. In situations where very
long cables are in use, the signal degradation could reduce network
performance. It is a good practice to use cables that are not any longer
than necessary.
Post by DrSkip
Post by Isaac M. Bavaresco
Use Cain&Abel (or other hackering software) to turn a switch into a hub
by
Post by Isaac M. Bavaresco
ARP Spoofing/routing table overflow.
Em qui, 30 de ago de 2018 02:46, Harold Hallikainen <
Post by Harold Hallikainen
I have a hub here that I use all the time with Wire Shark. Sometimes I
need to help someone debug something in the field, and they don't have
a
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
hub, and they are getting hard to come by.
Since 10/100 Ethernet uses two pair, one for transmit, and one for
receive, it SEEMS like it should be possible to make a resistive hub
where
Post by Harold Hallikainen
each transmit pair drives the receive pairs of the other two ports
(total
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
of 3 ports). I've done similar resistive networks for audio splitting
while maintaining impedances. But, I haven't figured out whether this
would work or what the resistor values would be. I did find a passive
hub
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
using a bunch of diodes, but it seems like resistors should work. I
also
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
see Ethernet taps where there are four ports. Data going one way
between
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
the other two ports shows up on one of the monitor ports while data
going
Post by Isaac M. Bavaresco
Post by Harold Hallikainen
the other way shows up on the other monitor port. This requires two
Ethernet ports on the computer running WireShark, which is a pain.
So, any ideas on this? Is it possible to use resistive splitters to
make
Post by Isaac M. Bavaresco
a
Post by Harold Hallikainen
passive hub?
Thanks!
Harold
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RussellMc
2018-08-30 13:31:51 UTC
Permalink
Post by Harold Hallikainen
I have a hub here that I use all the time with Wire Shark. Sometimes I
need to help someone debug something in the field, and they don't have a
hub, and they are getting hard to come by.
Using dnly
Inverse parallel pairs of diodes between
Wire 3 to wire 1 of other cables
Wire 2 to wire 6 of other cables

24 diodes

So diode pairs from

A1 to B3 & C3
B1 to A3 & C3
C1 to A3 & B3

A2 to B6 & C6
B2 to A6 & C6
C2 to A6 & B6

Here: http://www.zen22142.zen.co.uk/Circuits/Interface/pethhub.htm


Russell
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RussellMc
2018-08-30 13:46:06 UTC
Permalink
1. My prior post:

diodes only <- dnly

2. Useful discussion here on Stack Exchange EE (which all EE's should be a
member of (as well as PICList :-) ))

https://electronics.stackexchange.com/questions/10864/building-a-passive-ethernet-hub-with-anti-parallel-diodes?rq=1

Comment on diodes here.
1N4148 or 1N914 "should" work.

https://electronics.stackexchange.com/questions/150601/choosing-diodes-for-a-passive-ethernet-hub


____________________

Similar:

https://www.eeweb.com/circuit-projects/building-a-passive-ethernet-hub
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Allen Mulvey
2018-08-30 15:33:35 UTC
Permalink
Harold,

I have an old 8 port hub. It hasn't been used in 15 or 20
years but seems to still work. I would be glad to send it to
someone who could use it. Send me a mailing address offline.
The 5v 800ma power supply weighs a ton so I would prefer to
not send that.

Allen

-----Original Message-----
From: piclist-***@mit.edu
[mailto:piclist-***@mit.edu] On Behalf Of Harold
Hallikainen
Sent: Thursday, August 30, 2018 12:50 AM
To: Pic List
Subject: [EE] Passive Ethernet Hub?

I have a hub here that I use all the time with Wire Shark.
Sometimes I
need to help someone debug something in the field, and they
don't have a
hub, and they are getting hard to come by.

Since 10/100 Ethernet uses two pair, one for transmit, and
one for
receive, it SEEMS like it should be possible to make a
resistive hub where
each transmit pair drives the receive pairs of the other two
ports (total
of 3 ports). I've done similar resistive networks for audio
splitting
while maintaining impedances. But, I haven't figured out
whether this
would work or what the resistor values would be. I did find
a passive hub
using a bunch of diodes, but it seems like resistors should
work. I also
see Ethernet taps where there are four ports. Data going one
way between
the other two ports shows up on one of the monitor ports
while data going
the other way shows up on the other monitor port. This
requires two
Ethernet ports on the computer running WireShark, which is a
pain.

So, any ideas on this? Is it possible to use resistive
splitters to make a
passive hub?

Thanks!

Harold
--
FCC Rules Updated Daily at http://www.hallikainen.com
Not sent from an iPhone.
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list
archive
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peter green
2018-09-13 14:09:24 UTC
Permalink
Post by Harold Hallikainen
I have a hub here that I use all the time with Wire Shark. Sometimes I
need to help someone debug something in the field, and they don't have a
hub, and they are getting hard to come by.
Since 10/100 Ethernet uses two pair, one for transmit, and one for
receive, it SEEMS like it should be possible to make a resistive hub where
each transmit pair drives the receive pairs of the other two ports (total
of 3 ports).
There are a few problems.

1. Modern Ethernet hardware usually has auto-negotation and auto-mdix, these are very likely to get confused by any such contraption.
2. IIRC 100 megabit Ethernet continuously transmits a carrier even when not sending data. So afaict this a passive hub can only ever work for 10M.
3. If signal gets reflected back to the receive pair of the sender then the sender will detect false collisons. This is a problem because a resistive/combiner splitter will reflect power back out of it's other input. So signal can go from e.g. TX1 to RX2 to TX3 to RX1.

I belive point 3 is why the original design used diodes, to ensure any reflected back signals were sufficiently weakened that they would not cause false collisions.
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