Mac address changes

M

Thread Starter

Mario Bruno

Hi all

I need to change the mac address in some Ethernet card. The reason is to filter mac address in ethernet switches. We change this
address in siemens comunication card ( cp443 , cp1430 , cp1413 ). But I don't know, how to change in other cards ( for example: 3com ).
Can anybody help me?


Thanks in advance..

Mario F. Bruno
[email protected]
Dpto. Desarrollo y Mant.
Electronica e Instrumental
 
A

Alex Pavloff

This is not normally a user controlled operation. The PC-104 Ethernet cards that we use here have an SMC chip on them -- we have the software and cables needed to plug into a header on the PC104 board itself and change the MAC
address, but we manufacture the cards in the first place.

It would make sense to me that this should be handled at the switch level.
 
M
Dear Alex:

Thanks for your help. We have received some Siemens ethernet cards, without the manufacture's mac address indicated on them.
Then, we needed to assign a mac address, for each ethernet card, administered by us. ( to avoid repetitions ). Additionally, we use the same network plant for plc and office's PC, implementing filtering at switch level .
I agree with you, this is handled at level switch. But, we use our PLC programer via ethernet facilities, and in this
programer we don't use siemens card. The switches' filter have the folowing format:
08.00.06.**.**.** ( the siemens pattern ). And we add to this filter the entire mac address for other vendor, as a exception.

I think that is better to change the mac address in our PLC programmer ( to 08.00.06.**.**.** ) than make this change in the
switch , to avoid complications in the filtering switch.

May be exists, some cards ( no siemens ) that is possible to change its mac address. Do you know?

Regards
Mario

Mario F. Bruno
[email protected]
Dpto. Desarrollo y Mant.
Electronica e Instrumental
 
W
Mario,

Here is a possibility to hack the card:

You should be able to look up the Ethernet controller chip that's on the card. The MAC ID is usually held in an EEPROM (part number 93C46,
a small 8-pin device). The chip datasheet will tell the location (offset) of the MAC ID inside the EEPROM; you can either pull the part,
reprogram it, and put it back; or perhaps you can find a utility that will work with the card that will allow you to do this without removing the part.

Even most inexpensive (<$200) EPROM programmers can handle this chip. You could read the chip's contents in, patch the new MAC ID, then reprogram the chip. Before you change the ID, you should also save a file with the original contents of the part, in case you have to put it back. If it's an 8-pin miniDIP package, you could even install a socket so the part could be swapped or reprogrammed with more facility.

Happy hacking!

Willy Smith
Numatics
Costa Rica
 
H

Hullsiek, William

The MAC address should be able to be changed via an API call (maybe through NDIS).

Protocols such as DECnet phase IV, and LAT change the MAC address. So there should be an API call for setting the firmware in the board.


- Bill Hullsiek
 
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Mike Johnson

I thought that all MAC addresses, for the "Ethernet standard", was a controlled item under IEEE in order to prohibit the possibility of having duplicate addresses. Thus, helping to keep order in the world. If this is so, the end user should not have any access to the MAC chip's firmware. Unless, one downloads the opcode into a hex type editor and can translate/interpret what is probably the MAC chip instruction set, like machine code for a DSP chip or a Motorola chip.
 
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Chris Kellock

MAC addresses are controlled. But some devices can over-ride the hardware default with a software value. Many network cards allow for that, but I'm not sure about PLC devices and such.

MAC addresses are assigned by IEEE, and are unique. The only exception I've heard of is 3Com, who has begun to re-use their old MAC addresses from obsolete products like the 3C501 network card. Other than that, you should never see 2 devices with the same MAC address.

Chris
 
E

E. Douglas Jensen

Now there's the germ of a neat service someone could offer: re-programming MAC address EPROM's. There are a bunch of reasons people wish they could specify NIC MAC addresses.

Doug
--
E. Douglas Jensen (at home)
[email protected], http://www.real-time.org
Home voice 508-653-5653, home fax 508-653-3342
Cell phone: voice 508-728-0809; text http://www.bam.com/send2.htm
Pager 888-916-9802 and http://www.skytel.com/paging (PIN 8889169802)
Office voice 781-271-2514, office Fax 781-271-4686
 
D

Dave Ferguson

This is a kind of dangerous policy. Since in the end Ethernet cards communicate via the MAC address and they are unique and assigned, there is a possibility of duplicate Mac's which would cause total confusion on the network.

Reality is this is unlikely today but in the future with the use of high speed access into the home (last mile) syndrome, this could really cause
some trouble as an IP is resolved to a MAC and there are duplicates because people hacked them and changed them all. But this is similar to duplicate IP's out there.....

Just my 2 cents :)......

Dave Ferguson

Blandin Paper Company
UPM-Kymmene
DAVCO Automation
 
J

Johan Bengtsson

I agree that it is a dangerous policy, but not as dangerous as duplicated IP addresses.
Reason: duplicate MAC addresses is only a problem if it occurs at the same subnet, after a message passes a router (or if two might be needed) it won't be any problem if the same MAC address is used again, but if the same IP adress is reused
things can be quite confused.

I say it should be avoided if it is at all possible to avoid, but well, there might be reasons.... Be aware what you are doing however, things could be very confused....

/Johan Bengtsson

----------------------------------------
P&L, Innovation in training
Box 252, S-281 23 H{ssleholm SWEDEN
Tel: +46 451 49 460, Fax: +46 451 89 833
E-mail: [email protected]
Internet: http://www.pol.se/
----------------------------------------
 
B
If memory serves (it has been a little while since I worked with this) the 48-bit MAC ID/hardware address consists of a chip-
vendor-specific prefix and a 'unique' component. Therefore, all of Chip Vendor X's Ethernet chips might have the prefix 12:34:56:xx:xx:xx. If X sells chips to Company Y to be incorporated in Y's products, X may allocate a block of 'unique' components for Y to use, say 12:34:56:01:00:00 - 12:34:56:07:FF:FF. Company X may reserve 12:34:56:08:00:00 - 12:34:56:FF:FF:FF for its own
products (NICs and such). So, as long as companies maintain the prefix and ensure that the 'unique' components are within their alloted range and are unique, no duplicates occur.

Brian Lawry, Mfg Software Engineer
Compressor Controls Corporation
[email protected]
www.compressorcontrols.com
 
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E. Douglas Jensen

This is off the automation point somewhat, but let me give you an example of why it is so handy to be able to change a NIC MAC address.

A cable company ISP often uses the MAC address you give them and encodes it so that internet traffic functions only with that address. If you change PC's or NIC's, you have to call up the cable company ISP and wait and wait on hold and eventually speak to tech support and give them your new NIC MAC address; and what happens is that your service stops temporarily while they change the MAC address in their system.

It would be LOTS easier if you could keep the same NIC MAC address when you change NIC's/PC's/routers.

Doug
--
E. Douglas Jensen (at home)
[email protected], http://www.real-time.org
Home voice 508-653-5653, home fax 508-653-3342
Cell phone: voice 508-728-0809; text http://www.bam.com/send2.htm
Pager 888-916-9802 and http://www.skytel.com/paging (PIN 8889169802)
Office voice 781-271-2514, office Fax 781-271-4686
 
D

Darold Woodward

We are manufacturing Ethernet processor cards (SEL-2701) and the process is very similar to what you describe. Our address space is unique, so we never duplicate another vendor's mac addresses. We also make each card unique within our address space. Therefore, you should never need to configure the mac address.

While we set the mac address with software (as part of manufacturing), it is a "calibration level" function and we do not document the process for end users.

Your bridge, router, or "bridge-router" should have sufficient programmability for your application to deal with the different ranges of mac addresses used by different manufacturers. If it does not, you are not using the correct device or the correct approach to solve your problem.

For example, if you are trying to selectively route a non-routable (level 3 non-routable) protocol then you must use a bridge-router with enough horsepower as a router to get the job done so that you don't pass a bunch of traffic over
the other segments (WAN links, etc.) and melt down your system.

Darold Woodward PE
SEL Inc.
[email protected]
 
I've never heard fo an ISP locking it down to the MAC address of your computer. Typically the one they are insterested in is the MAC address on the cable modem itself. It has an ethernet port and that's the MAC address they asked me for when I moved from one service area to another. They had
no interest in my computer's MAC address.

CK
 
W
Another thing to consider is that some inexpensive cards do *not* use unique addresses. Of course the majors use unique addresses, but some of the low-end ones don't bother. If they did, you probably couldn't buy the cards at Fry's for ten bucks.

Willy Smith
Numatics
Costa Rica
 
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Hullsiek, William

This topic should be called ISP hack, but I gave the ISP the MAC address of my NAT (Network Address Translator) on my home network. This will map an internal IP address into a DHCP assigned IP address. This reduces the probability of someone discoverying my home computer by accident. Some ISP's use the MAC address to safeguard home users from hackers. The MAC address can be used to configure their firewall software. Replacement process of the NAT is to configure the old MAC address into the firmware. This 'hides' the detail of your home network from the rest of the world. However, there is a need to 'configure' the MAC address, especially for legacy protocols such as DECnet. (There probably are others). The DECnet protocol has its own 'vendor' portion of the address, then assigned group/node numbers into the 'serialized' portion. An end-node, can then filter on the mac address, which prevents excess servicing of ethernet packets (not intended for the end-node). You always can place yourself into promiscuous mode, and listen to everything on the network. But that is a hack of a different colour. But depending on the application and network protocol in use, there is a need to manipulate the MAC address. However, 'best-practices' should be to use the default MAC address of the card. While I may be laughed at, AppleTalk was a nice little protocol, because it was 'auto-configuring' to most part. - Bill Hullsiek
 
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Gary Drake Cargill Fertilizer Inc.

In our DCS system all the nodes have a defined mac addresses that is fixed, when ever we change out hardware we have change the mac address to match the node address, otherwise we would have to change the config files on all the other nodes. Gary Drake Cargill Fertilizer 8813 Hwy 41 South Riverview, Fl 33569 tel (813)671-6213 fax (813)672-6438
 
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Johan Bengtsson

I don't agree! That would mean that you couldn't use two of them in the same network. I do NOT think they have the same adress, programming unique numbers into IC:s can be fully automated and don't need to cost that much for high volumes. ---------------------------------------- P&L, Innovation in training Box 252, S-281 23 H{ssleholm SWEDEN Tel: +46 451 49 460, Fax: +46 451 89 833 E-mail: [email protected] Internet: http://www.pol.se/ ----------------------------------------
 
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Dave Ferguson

That is great provided you do not sell the old one when you change to the guy down the street and he gets the same ISP and guess what.............you have just created a problem on the Internet. If we knew everyone would use a unique address, this would work great but since YOU cannot guarantee it, lets stick with the system as designed instead of FIXING it.... Dave Ferguson Blandin Paper Company UPM-Kymmene DAVCO Automation
 
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