Ethernet Switch -- Managed versus Unmanaged

Ethernet Switch -- Managed versus Unmanaged
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Subject Author Date
Ethernet Switch -- Managed versus Unmanaged Heinz-Gerd Schlagregen 01-28-2007
Posted by Heinz-Gerd Schlagregen on January 28, 2007, 1:43 pm
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Hi,



basically a switch works only with the hardware addresses of the attached
devices. A switch is a high speed device. It is meant to connect a number of
ports delivering full speed to each single one of them, It's internal
operation speed is at least equal to the sum of the maximum throughput of
all ports.



Since it is working just with hardware addresses it does not need an IP
address for its operation. If you want to control its operation counting
packets, bytes, errors an so on you will need a function collecting these
information on the switch.

Since this idea was developed quite a while ago many requirements have been
expressed by the industry getting to the point of realization that without
this knowledge a network is uncontrollable.



Every company launching switches to the market does secret manipulations to
frames and data passing through the switch to make it as fast as possible.
They build their very own switch. But all vendors will have to be able to
function together in the same network. No problem, at the input and at the
output ports the have to stick to the standard 802.3d.



But how would I control this mixture of switches for statistical reasons.
Counting bits and bytes and frames and packets is not that easy in a world
without a standard solution for this problem?



The first idea was to develop a standard databank being held on either
switch. The firmware would have its device describtion tables located at a
neat place like port enabled or disabled, full duplex or half duplex an so
on. Besides these data the firmware could count packets, errors, frames ...
and increase the counters in the databank.



This databank is called MIB. It stands for Management Information Base. It
is a standard and is written with a special compiler called ASN.1 (Abstract
Syntax Notation.One). The compiler is very small and has a very view
commands. The structure is fixed in an RFC. Every vendor supporting this
feature would have to apply to the requirements and put system information
for example at the same location like the competing companies.



To gain this information you had to go to the switch and attach a pc with
appropriate software to the RS232 port on the switch to be able to read the
MIB. This is rather inconvenient. Much more convenient would be to stay at
the office and have a network connection to the switch.



We would need an IP address on the switch to be able to connect to any
switch in any network To communicate with this switch we would need some
functions of the layer 3 IP stack on the switch. This would make it possible
to send a frame to the switch. Who should do the work getting the
information from the MIB? Who would check the authentication of this frame?
It would not be a good idea to let anyone take a look at your MIB. For this
purpose a special peace of software was developed called SNMP (Simple
Network Management Protocol) It is simple because it uses UDP, means you
will get no acknowledge for any frame.



We could continue now into the historical development of versions of SNMP
v1, v2c and v3.



The true and only reason to give an IP address to a switch is to gain
control over the device. SNMP can read and write information for you from
and to the MIB. A so called trap frame can be sent by the device unsolicited
if important events happen causing an alarm.



I have tried to keep it as short as possible and still keep it
understandable.

If you have further questions feel free to contact me under
heinzgerd.schlagregen@freenet.de



HG.Schlagregen

Germany



Betreff: Ethernet Switch -- Managed versus Unmanaged
Datum: Donnerstag, 25. Januar 2007 21:33

Hi,

I'm designing an Ethernet Switch and one of the requirements is that
the IP address of the device be fixed to a port, i.e port 1 would
always have IP XYZ, can this be done with an unmanaged ethernet switch?

Thanks for the help.

GC



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Posted by glen herrmannsfeldt on January 29, 2007, 3:13 am
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Heinz-Gerd Schlagregen wrote:

> basically a switch works only with the hardware addresses of the attached
> devices. A switch is a high speed device. It is meant to connect a number of
> ports delivering full speed to each single one of them, It's internal
> operation speed is at least equal to the sum of the maximum throughput of
> all ports.

As well as I remember, the OP was asking for IP address filtering.
There are some security situations where that might be useful.

> Since it is working just with hardware addresses it does not need an IP
> address for its operation. If you want to control its operation counting
> packets, bytes, errors an so on you will need a function collecting these
> information on the switch.

One could add the simplest IP address filtering onto unmanaged switch
logic. There would have to be some way to get the addresses in, but
that could be done with much less than a traditional manages switch.

There might be some restrictions on IP packets, especially no
fragmentation before the appropriate IP address (which there shouldn't
be anyway, but as I understand it, that is a favorite way to get around
some security systems.)

I don't know that it is likely that anyone will build one, but it is
possible. One could even put in permanent MAC addresses in for
filtering purposes.

-- glen


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other useful resources:
The Federal Communications Commission (FCC)
Telecommunications Industry Association
Electronic and Software Security Products and Services
International Telecommunication Union

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