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Change MAC address

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Anonymous
January 25, 2005 8:53:27 AM

Archived from groups: comp.dcom.lans.ethernet (More info?)

Hi,

I have 2 networking devices which are the same. But the MAC addresses
can be changed. When I connect them to a hub, do I need to change the
MAC address so that they have different MAC addresses?

Thanks!

More about : change mac address

Anonymous
January 25, 2005 3:14:11 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

leonlai2k@yahoo.com wrote:

> Hi,
>
> I have 2 networking devices which are the same. But the MAC addresses
> can be changed. When I connect them to a hub, do I need to change the
> MAC address so that they have different MAC addresses?

Are you saying they have the same mac? That's unual. Some computer NICs
can be changed, but without further info, I haven't any idea about what
you've got.
Anonymous
January 25, 2005 4:22:20 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

leonlai2k@yahoo.com wrote:
>I have 2 networking devices which are the same. But the MAC addresses
>can be changed. When I connect them to a hub, do I need to change the
>MAC address so that they have different MAC addresses?

What kind of devices?

In general (plus or minus the discussion in this ng about what happens
or how it should be handled when two MAC addresses are the same),
every single MAC address should be globally unique.
Related resources
January 25, 2005 6:01:48 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

On 25 Jan 2005 05:53:27 -0800, leonlai2k@yahoo.com wrote:

> Hi,
>
> I have 2 networking devices which are the same. But the MAC addresses
> can be changed. When I connect them to a hub, do I need to change the
> MAC address so that they have different MAC addresses?
>
> Thanks!

The mac addresses should be different anyway. What type of devices are
they, NICs?

Regards

Bill
Anonymous
January 25, 2005 8:17:12 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

William P.N. Smith wrote:

> In general (plus or minus the discussion in this ng about what happens
> or how it should be handled when two MAC addresses are the same),
> every single MAC address should be globally unique.

However, unique MACs are only required on the local network. One you pass
through a router, the original MAC is lost, along with the rest of the
original ethernet (or other) frame.
Anonymous
January 25, 2005 10:05:04 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

In article <jf3dv0551lelpgkckb2qe1ajdpnh6gpn1q@4ax.com>,
<William P.N. Smith> wrote:

:In general (plus or minus the discussion in this ng about what happens
:o r how it should be handled when two MAC addresses are the same),
:every single MAC address should be globally unique.

Though that's not the underlying definition: the underlying
requirement is not -global- uniqueness, but rather uniqueness
per segment.
--
Reviewers should be required to produce a certain number of
negative reviews - like police given quotas for handing out
speeding tickets. -- The Audio Anarchist
Anonymous
January 25, 2005 11:51:48 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

William P.N. Smith wrote:
>every single MAC address should be globally unique.

OK, they only have to be unique per segment to make that particular
segment work, but in general, they should be globally unique, so any
device will work on any segment with any other device. And yeah,
there are nits you can pick all day, but I suspect the OP needs to
give them (globally) unique addresses.
Anonymous
January 26, 2005 12:28:14 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

William P.N. Smith wrote:

> William P.N. Smith wrote:
>>every single MAC address should be globally unique.
>
> OK, they only have to be unique per segment to make that particular
> segment work, but in general, they should be globally unique, so any
> device will work on any segment with any other device. And yeah,
> there are nits you can pick all day, but I suspect the OP needs to
> give them (globally) unique addresses.

Hopefully, he can find unique addresses. There are only 281 trillion of
them available. ;-)
Anonymous
January 26, 2005 10:36:42 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

In article <jf3dv0551lelpgkckb2qe1ajdpnh6gpn1q@4ax.com>,
<William P.N. Smith> wrote:
>leonlai2k@yahoo.com wrote:
>>I have 2 networking devices which are the same. But the MAC addresses
>>can be changed. When I connect them to a hub, do I need to change the
>>MAC address so that they have different MAC addresses?
>
>What kind of devices?
>
>In general (plus or minus the discussion in this ng about what happens
>or how it should be handled when two MAC addresses are the same),
>every single MAC address should be globally unique.

Normally, a NIC will be shipped from the factory with a globally unique
MAC address. One exception to this is when you have multiple NICs in a
SUN computer. In that case, the default is to have one MAC address for
all the NICs in the machine. The idea is that the address is for the
computer, not the NIC and that there would be no reason to have more than
one NIC connected to an ethernet segment. You can change this default
and have a seperate MAC address for each NIC by setting a value into the
correct variable in the open boot program.
--
Tom Schulz
schulz@adi.com
January 26, 2005 11:09:20 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

"James Knott" wrote:
> William P.N. Smith wrote:
>
> > William P.N. Smith wrote:
> >>every single MAC address should be globally unique.
> >
> > OK, they only have to be unique per segment to make that particular
> > segment work, but in general, they should be globally unique, so any
> > device will work on any segment with any other device. And yeah,
> > there are nits you can pick all day, but I suspect the OP needs to
> > give them (globally) unique addresses.
>
> Hopefully, he can find unique addresses. There are only 281 trillion of
> them available. ;-)

I'm sorry I cannot share your optimism... After setting the Individual/Group
address bit to 0 and the Universally or Locally administered address bit to
1, there are only about 70 trillion possible combinations left! ;-)

(See IEEE Std 802-2001 subclause 9.2 for more details.)

Michael
(remove filter from email address)
--
http://www.ethernetinthefirstmile.com
Anonymous
January 26, 2005 11:09:21 PM

Archived from groups: comp.dcom.lans.ethernet (More info?)

Michael wrote:

>> Hopefully, he can find unique addresses.  There are only 281 trillion of
>> them available.  ;-)
>
> I'm sorry I cannot share your optimism... After setting the
> Individual/Group address bit to 0 and the Universally or Locally
> administered address bit to 1, there are only about 70 trillion possible
> combinations left! ;-)

Maybe we'd better start salvaging the MACs from all the NICs that have been
trashed over the years. ;-)
!