manufacturer assigned macs are guaranteed to be globally unique.
A specific enterprise reconfiguring the mac is akin to an enterprise
using RFC1918 space.
Hello Whoever ,
manufacturer assigned macs are guaranteed to be globally unique.
Theoretically. I didn't experience it personally, but I believe there
was at least one fairly well known event a few years back where a
manufacturer shipped cards with duplicated UAAs.
A specific enterprise reconfiguring the mac is akin to an enterprise
using RFC1918 space.
Fortunately, this practice rarely occurs these days (token ring / SNA
shops often did this) although I'd be curious if anyone still does it.
Unfortunately, in my opinion, some of the relevant lessons learned from
using LAAs (and their demise) didn't take hold at layer 3.
John
There was another manufacturer one of the really low budget cards, I
forget the brand but they were shipped in a box which looked like a
dunkin's munchkins box. If you bought several boxes of these, I think six
in a box and the entire package was $30 you were likely to find more than
2 or 3 with the same addressing.
These were 10 meg only and I can't for the life of me remember the brand.
Used the tulip driver for linux if that helps refresh memories.
box:~ # /sbin/lspci | grep 'Happy'
01:03.1 Ethernet controller: Sun Microsystems Computer Corp. Happy Meal
(rev 01)
box:~ # /sbin/ifconfig | grep 'eth'
eth0 Link encap:Ethernet HWaddr DE:AD:BE:EF:00:B0
eth1 Link encap:Ethernet HWaddr DE:AD:BE:EF:00:B1
eth2 Link encap:Ethernet HWaddr DE:AD:BE:EF:00:B2
eth3 Link encap:Ethernet HWaddr DE:AD:BE:EF:00:B3
It didn't come with it's own MAC address pre-programmed...
- d.
Mr. James W. Laferriere wrote:
Hello Whoever ,
manufacturer assigned macs are guaranteed to be globally unique.
A specific enterprise reconfiguring the mac is akin to an enterprise
using RFC1918 space.I have to agree with Mr. Shore here . Mac addresses are NOT
unique from ALL manufacturers '.' . I do beleive that there was a
a brand (maybe not USA) that the cadr came without mac-address
hard assigned on the card , You HAD to , using their
configuration tool assign one . JimL
There was actually a fly by nighter that had one
of the earliest EISA based 100mps FD FE in the early 90's,
where ALL there cards had the SAME MAC, the people
issuing ranges had only assigned them the ONE...
So, they burned it on all their cards!
Really.
Obviously, you could only use one per network... 
And, FWIW, old VAX gear had assignable MAC's....
But, other than freak cases, the original point
is true.. today most MAC's are globally unique.
HSRP not withstanding.....
(To every rule, there is an exception, including this one.)
* sigh *
s/there/their/
s/mps/mbs/
s/:)/:}/
Richard Irving wrote:
"Dominic J. Eidson" wrote:
> Fortunately, this practice rarely occurs these days (token ring / SNA
> shops often did this) although I'd be curious if anyone still does it.box:~ # /sbin/lspci | grep 'Happy'
01:03.1 Ethernet controller: Sun Microsystems Computer Corp. Happy Meal
(rev 01)
box:~ # /sbin/ifconfig | grep 'eth'
eth0 Link encap:Ethernet HWaddr DE:AD:BE:EF:00:B0
eth1 Link encap:Ethernet HWaddr DE:AD:BE:EF:00:B1
eth2 Link encap:Ethernet HWaddr DE:AD:BE:EF:00:B2
eth3 Link encap:Ethernet HWaddr DE:AD:BE:EF:00:B3It didn't come with it's own MAC address pre-programmed...
Sun, by default, loads their manufacturer ID as the first three bytes
and uses the system ID (burned into the *mumble-mumble* chip on the
motherboard) in the last three. Since the sysID is unique this guarantees
global uniqueness.
This also means, by default, all NICs in a Sun have the same MAC. This
is considered a feature. There is a knob in the EEPROM, 'local-mac-address?',
that will use the MAC address(es) burned into the card rather than the
sysID. However, for a NIC integrated into the motherboard, like an hme,
there is no "local" MAC, just the sysID.
I would say _supposed_ to be unique. Surely some cheapo manufacturer has recycled addresses from their old ISA card days.
Back in the mainframe days, admins used to always set the MAC addresses of devices on the token rings, since the MAC address was used to bid on which node managed the ring. I have seen people fat-finger it too.