Hi
I want to assign mac addres to virtual adpater and mac
address should be like that if it should not create
problem in arp resoultion(i.e. mac address should be
as real card which able to comunicate on lan )
waiting for ur reply,
Anil
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On Sun, 4 Dec 2005, anil dahiya wrote:
> I want to assign mac addres to virtual adpater and mac
> address should be like that if it should not create
> problem in arp resoultion(i.e. mac address should be
> as real card which able to comunicate on lan )
You may be able to get away with using a MAC address
inside the OUI range that XenSource registered.
--
All Rights Reversed
Followup to: <[email protected]>
By author: Rik van Riel <[email protected]>
In newsgroup: linux.dev.kernel
>
> On Sun, 4 Dec 2005, anil dahiya wrote:
>
> > I want to assign mac addres to virtual adpater and mac
> > address should be like that if it should not create
> > problem in arp resoultion(i.e. mac address should be
> > as real card which able to comunicate on lan )
>
> You may be able to get away with using a MAC address
> inside the OUI range that XenSource registered.
>
Any MAC with bit 0 clear and bit 1 set in the first octet is "local
use"; the best thing to do (unless you have your own OUI) is just to
pick a random address inside this range. You should only run into
collision problems when you get close to 2^23 hosts on a network.
-hpa
On Dec 4, 2005, at 2:41 PM, H. Peter Anvin wrote:
> Followup to: <Pine.LNX.
> [email protected]>
> By author: Rik van Riel <[email protected]>
> In newsgroup: linux.dev.kernel
>>
>> On Sun, 4 Dec 2005, anil dahiya wrote:
>>
>>> I want to assign mac addres to virtual adpater and mac
>>> address should be like that if it should not create
>>> problem in arp resoultion(i.e. mac address should be
>>> as real card which able to comunicate on lan )
>>
>> You may be able to get away with using a MAC address
>> inside the OUI range that XenSource registered.
>
> Any MAC with bit 0 clear and bit 1 set in the first octet is "local
> use"; the best thing to do (unless you have your own OUI) is just to
> pick a random address inside this range. You should only run into
> collision problems when you get close to 2^23 hosts on a network.
Theoretically that is true, however there are usages that have been
approved that violate that principal. One was for TI Token Ring
chips. They were completely unable to use "global" MAC addresses -
the local bit always had to be set. Since TI could/would not fix
their chips, using the local address became allowed for a universally
unique address.
This method was later used by Apple on Ethernet for their DOS card.
The Macintosh environment would get the global address and the DOS
card would get the local one through the shared ethernet port. You
might think that you can ignore the token ring case, but you'd be
wrong - there are ethernet/token ring bridges deployed. The Apple
case is also best not ignored. I don't know how many others may be
doing similar things.
So, I would not advise anyone to simply believe that they can use the
entire local MAC address space safely. You are also very likely to
have trouble if there is any DECnet usage in the area. Anyone else
notice that DECnet kernel patch recently? Someone must still be using
it...
This is an instance where Linus' comment a few weeks ago regarding
specs vs. reality comes into play. This is kind of an obscure area so
not a whole lot of people know about some of these things. Don't
believe everything you read in magazines regarding MAC addresses
either. I've seen some very bad advice there from time to time in
this particular area.
I would recommend using the same MAC address with the local bit set
(as Apple did) for a single additional address. If you need more
addresses and need them to be visible on the LAN, I don't know of a
reliable, generic solution off the top of my head.
--
Mark Rustad, [email protected]
Mark Rustad wrote:
>
> Theoretically that is true, however there are usages that have been
> approved that violate that principal. One was for TI Token Ring chips.
> They were completely unable to use "global" MAC addresses - the local
> bit always had to be set. Since TI could/would not fix their chips,
> using the local address became allowed for a universally unique address.
>
> This method was later used by Apple on Ethernet for their DOS card. The
> Macintosh environment would get the global address and the DOS card
> would get the local one through the shared ethernet port. You might
> think that you can ignore the token ring case, but you'd be wrong -
> there are ethernet/token ring bridges deployed. The Apple case is also
> best not ignored. I don't know how many others may be doing similar
> things.
>
> So, I would not advise anyone to simply believe that they can use the
> entire local MAC address space safely. You are also very likely to have
> trouble if there is any DECnet usage in the area. Anyone else notice
> that DECnet kernel patch recently? Someone must still be using it...
>
> This is an instance where Linus' comment a few weeks ago regarding
> specs vs. reality comes into play. This is kind of an obscure area so
> not a whole lot of people know about some of these things. Don't
> believe everything you read in magazines regarding MAC addresses
> either. I've seen some very bad advice there from time to time in this
> particular area.
>
> I would recommend using the same MAC address with the local bit set (as
> Apple did) for a single additional address. If you need more addresses
> and need them to be visible on the LAN, I don't know of a reliable,
> generic solution off the top of my head.
>
By definition, using local addresses is probabilistic. There are moron
hardware manufacturers, as you show above (which aren't even the worst
of the lot, from what I've seen), but your cross-section with other
local-address users will be very small (collision only likely around
2^23 nodes.)
Reducing the address space available to randomly pick from will only
increase the likelihood of failure.
This is an instance where an understanding of statistics come into play.
-hpa
On Sun, 4 Dec 2005 11:29:58 -0800 (PST)
anil dahiya <[email protected]> wrote:
> Hi
> I want to assign mac addres to virtual adpater and mac
> address should be like that if it should not create
> problem in arp resoultion(i.e. mac address should be
> as real card which able to comunicate on lan )
>
> waiting for ur reply,
> Anil
>
use random_ether_addr (see include/linux/etherdevice.h)
--
Stephen Hemminger <[email protected]>
OSDL http://developer.osdl.org/~shemminger