AT&T Cable uses Mac ID
Leonard Evens
service works which may be of use to others. It is a long sad tale, so
bear with me, because you might find the punch line interesting.
The whole thing started because I was foolish enough to change my TV
cable package. When that took effect, I lost my internet connection.
After lots of time on the phone talking to the higher
echelon techs, we discovered that long ago, perhaps even
when Mediaone owned the cable company, someone entered the
wrong number of connections in my house in their database As a result,
when I changed the TV package, their program suspended my internet service.
I normally use a Linksys dsl/cable router, but to try to get me connected
again, the AT&T techs of course insisted that the cable modem be
connected directly to a computer running Windows. They also wanted
me to power off/on the modem, which resulted in something like a half
hour wait or longer before it managed to negotiate a connection with the
AT&T network.
In any case, eventually the modem made a connection and I got an IP
address which was different from the one assigned earlier and
which I had in fact been using since the Excite->AT&T
switchover/disaster. This was of course with the modem connected
directly to the ethernet card in the computer.
I then reconnected everything through the dsl/cable router, and strange
things started happening. I remained connected in the sense that my
browsers (on two different machines using the router) saw the internet.
But I couldn't connect to my office computer in which I had jury rigged
the firewall so it had to know my home IP address. The problem, I
discovered was that my router kept using the old IP address which had
been active until AT&T suspended my account, and nothing I could
do could convince it to use the new address. I tried renewing the
lease to the wan. I tried switching to static addressing using the new
address, which did work, but when I switched back to dynamic addressing
it came back with the old address again. I even powered off/on the
router, but that also made no difference.
Finally, I remembered from a previous newsgroup discussion that AT&T was
using the Mac ID to verify its connection. I also remembered that
someone had noted that the Linksys allowed you to clone any Mac ID you
wanted. With a little effort, I found where the Linksys firmware had
hidden that option---not where the manual said it would be---and cloned
the hardware address of the ethernet card the cable modem had been
connected to when the connection was made. I then renewed the lease,
and Voila! I got the new IP address they had assigned me. I then got into
my office computer by an alternate route and told it what it needed to
know, and now everything is back to normal.
I am still a bit confused about just what was going on with the Linksys
router. My conjecture is that AT&T never recovered the original IP
address and in fact it is still assigned to the native Mac ID of the
router. So when their network saw the router it used that address. On
the other hand something else in their system knew what the new address
was and when my office computer tried to access the old address to verify
ssh, it wouldn't accept it. If anyone has a better idea of what was
going on, I would be interested in hearing it.
I presume that if I had turned off both router and modem, then when I
turned them on again, a new connection might have been made using the
native Mac ID of the router. But I don't want to chance disconnecting
the modem from their network if I don't have to, given how long it took
to reestablish a connection. I certainly hope I don't have to go
through the whole thing again, including spending an hour or more on the
phone the next time we have a power failure!
--
Leonard Evens l...@math.northwestern.edu 847-491-5537
Dept. of Mathematics, Northwestern Univ., Evanston, IL 60208
itallushrt
here is not rocket science. AT&T, just like 99.9% of the rest of cable modem
providers, uses Cisco UBRs (Universal Broadband Routers) as their CMTS
(Cable Modem Termination System). It is essentially a 7200 series router
with MC16x Cable Blades - each consisting of 5 upstream ports and 1
downstream port. Your modem will allow you to "surf" with any IP you assign
to it, granted its in use and routed on the network your on, thus that is
why you were still working with the old IP. Second, the subject line "AT&T
Cable uses MAC ID" is true for any cable modem system. The modems are
authorized, deauthorized, provisioned, etc depending on the HFC MAC ID of
the modem using Cisco's CNR server software (basically DHCP for Cisco Cable
modem networks). Just like a Ethermac on a NIC HFC MACs are unique MAC
address (they even have vendor codes just like ethermacs) and thus are the
perfect way to create a truly unique modem. When the Help Desk tech had you
power cycle it was due to the fact that he cleared the host off the UBR, and
more than likely made a provisioning request to someone in their
Provisioning Dept to push a new tftp file (.cm file or a small binary that
configs your modem) to your modem. Since AT&T uses provisioning on a per
modem basis to prevent a "wide open" cable network in which anyone with a
DOCSIS modem could plug it in and work (believe me this is more common than
you might think) it wasn't until this request was filled manually by someone
that your modem was registered once again on the UBR. Thus your service
began to work again once you pulled a new IP. Now, if AT&T has your .cm
file set to (or you purchase a QOS which allows I should say) allow more
than one CPE address than you can have multiple routable IPs assigned to
host behind your modem. Thus you could have your Linksys with one IP and
another host with another Routable IP. (Dunno, if the Linksys will act
simply as a bridge and not try to NAT the IP or not ??). Anyway. This is
nothing new, all cable modem ISP's do the same thing. It appears that in
your case, once again human error was the problem.
thanks,
itallushrt
"Leonard Evens" <l...@math.northwestern.edu> wrote in message
news:20020205.083753...@math.northwestern.edu...
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Leonard Evens
<itall...@hotmail.com> wrote:
Your explanation below is helpful. Unfortunately, it is technical enough
that I'm not sure I follow it all. I think perhaps I now see why the
old ethernet address continued to work. But there are still some things
I don't understand.
1. You don't mention the MAC address of the ethernet card and/or the
dsl/cable router itself. I understand that the network has to use the
Mac address of the cable modem. But why did it keep assigning the
old IP address until I cloned the Mac address of my computer's
ethernet card in the router? Or am I missing something?
2. Again, when talking about MAC addresses, are you saying that
all cable providers use the MAC address not only of the cable modem
but also the ethernet card or whatever the cable modem is attached to
on my end?
itallushrt
In response to your personal email.
1. The reason that the UBR kept assigning the old IP to that same Ethermac
is due to the host entry on the UBR. I must have been wrong earlier about
the tech clearing the host entry on the UBR. The UBR has a ARP entry for
both modem mac and ethermac.
2. see above.
"itallushrt" <itall...@hotmail.com> wrote in message
news:u600bl6...@corp.supernews.com...
Version: 6.0.320 / Virus Database: 179 - Release Date: 1/30/2002
Bill Cattell
> I am a NOC Engineer for a Cable modem ISP and can tell you what is going
> on here is not rocket science. AT&T, just like 99.9% of the rest of
> cable modem providers, uses Cisco UBRs (Universal Broadband Routers) as
snip
>
>
Since you're on that side of the industry I have a question you might be
able to answer... I have AT&T cable access and a Motorola Cybersurfer
Wave cablemodem. When I signed up with TCI @Home three years ago I had
two public addresses and could access the web through both addresses at
the same time, i.e. the cable modem would pass all traffic to the net.
I've recently ordered an addtional address from AT&T but when I try to
put a second PC into the hub the first connection dies. I've already
swapped hubs, NICs and patch cables. It's a case of either / or...
AT&T can't seem to figure out how to fix it. My understanding of the
cablemodem and broadband technology (which is limited) tells me that
there needs to be some change made to the cablemodem's internal
configuration. Is this correct?
My apologies for tossing this your way but you're the most knowledgeable
person in this area I've seen in here. AT&T's tech support has proven
worthless to this point. Maybe their level-three support team is so busy
due to the incompetance of the 1st and 2nd level teams... I don't know.
TIA,
Bill
N/A
`wcattell...@attbi.com' posted on `comp.os.linux.misc'
USENET newsgroup wrote:
Sounded like you have a basic cable modem service. If you want
to have additional IP address, you will pay $4.95 (check with
your provider) for additional IP address. This feature is
called home networking service under AT&T, IIRC.
Leonard Evens
<wcattell...@attbi.com> wrote:
I was told there was no level higher than level 2.
>
> TIA,
>
> Bill
Bill Cattell
> In article <c7va8.49485$Pz4.272366@rwcrnsc53>, "Bill Cattell"
> <wcattell...@attbi.com> wrote:
>
>> On Tue, 05 Feb 2002 10:07:56 -0600, itallushrt wrote:
>>
snip
>>
>> My apologies for tossing this your way but you're the most
>> knowledgeable person in this area I've seen in here. AT&T's tech
>> support has proven worthless to this point. Maybe their level-three
>> support team is so busy due to the incompetance of the 1st and 2nd
>> level teams... I don't know.
>
> I was told there was no level higher than level 2.
>
I was guessing at them having a level 3 support team. I've talked with
level 2 a couple times and have not been impressed. When I signed up
three years ago (then TCI / @Home) there was a level 3 and they were
pretty good - at least the two guys I talked to.
Bill
>
>> TIA,
>>
>> Bill
>
>