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aefstoggaflm
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General questions on encoded mac address(es)

#1 I saw these two FAQs

a) »RCN Forum FAQ »How to Check your Cable Modem ID -- Encoded MAC Address.

b) »RCN Forum FAQ »Why do we ask for encoded mac addresses?

#2 Does an encoded mac address only exist on Cable Modems?

#3 Is RCN the only Cable ISP that will request that info from it's user?

#4 Is it like IPv6?

Thanks
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WireHead
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#2 No, not by a long shot. I've seen automation networks with millions of devices all with encoded MACs.

#3 »RCN Forum FAQ »Why do we ask for encoded mac addresses?

Hope this helps.
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cramer
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reply to aefstoggaflm
#2 No. Every NIC has a unique MAC (unless we're talking about seriously old Sun hardware, which has a hostid used to create a MAC -- which is applied to all the NICs in the device... it was a Bad Idea 30 years ago, too.)

#3 The "encoded MAC" is an RCN thing so people aren't posting the modem ID in public. Thus, yes, RCN will be the only ones asking for it. (they're the only ones who can make any sense of it anyway)

#4 Absolutely not.


aefstoggaflm
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said by WireHead:

#2 No, not by a long shot. I've seen automation networks with millions of devices all with encoded MACs.

Ok.

How would someone not on using a Cable modem get the encoded MAC Address of their DSL modem?

My DSL modem is the Westell F90-610015-06

said by cramer:

It was a Bad Idea 30 years ago, too

If the reason for that being bad is not, is applied to all the NICs in the device then why is it bad?

If the reason for that being bad is, is applied to all the NICs in the device, is there any other reason besides that?

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cramer
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RCN's point is to not post your HFC (cablemodem) MAC in public where someone could (in theory) use it to clone your modem. I'm not aware of that being much of a problem these days.

The problem with the old Sun one-MAC-per-machine method was having every NIC on the system having the same MAC. A MAC is, by definition, supposed to be UNIQUE. If you're assigning the same MAC to multiple interfaces, it's not so unique. It becomes a serious problem when you attach more than one of those NICs to the same physical network. If you plug NIC1 and NIC2 into the same switch, it'll confuse the shit out of it; the same MAC is on multiple ports. If you run them to different switches, you'll have the same problem further out in the network if those two switches are ever connected -- you have to have an "A" network and "B" network that are completely physically isolated. (many switches will be confused even with VLAN logical isolation.)