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Bronze Star Contributor
anon86290
Posts: 209
Registered: ‎09-02-2003

Three Modem Questions

[ Edited ]

Hi,

 

I've got a Comcast branded Scientific Atlanta DPX2100 cable modem.  It goes to a CentreCOM MR820TR Microhub repeater, which feeds one computer.

 

1) When I log into the modem's home page, I see the modem's MAC.  If I do an ipconfig/all, I can't see the modem's MAC, only the physical address of my "Intel Pro/100 VE Network Connection.  How do I see the modem's MAC using a cmd or Windows (XPHome), or is that possible with a hub inbetween?

 

 

2) Also, on the modem's home page, on the status page, it shows this.  What is this?

 


CONNTECTED TO:              MAC ADDRESS:
--------------              --------------------------------------------------------------------
Ethernet PortEthernet
PortEthernet                00:06:F2:ea:d0:6h20:0f:1a:15:6d:2000:15:72:a7:1e:4500:26:46:ee:5a:8c
PortEthernet Port

3) And one more question...the modem's IP shows 73.71.xxx.xxx, and the Local Area Connection in Windows shows 67.188.xxx.xxx, as does ipconfig/all.  Why the difference?
 Thank you very much.
Message Edited by anon86290 on 04-24-2009 06:51 PM
Connection Expert
EG
Posts: 44,219
Registered: ‎12-24-2003

Re: Three Modem Questions

First. May I ask why you are using the CentreCOM hub ?
Connection Expert
JamesR
Posts: 6,438
Registered: ‎09-29-2007

Re: Three Modem Questions

[ Edited ]

anon86290 wrote:

Hi,

 

I've got a Comcast branded Scientific Atlanta DPX2100 cable modem.  It goes to a CentreCOM MR820TR Microhub repeater, which feeds one computer.

 

1) When I log into the modem's home page, I see the modem's MAC.  If I do an ipconfig/all, I can't see the modem's MAC, only the physical address of my "Intel Pro/100 VE Network Connection.  How do I see the modem's MAC using a cmd or Windows (XPHome), or is that possible with a hub inbetween?

 

Message Edited by anon86290 on 04-24-2009 06:51 PM

I don't know of any specific cmd that will display the modem MAC address, but you can do  ---   C:\> start iexplore 192.168.100.1 ---  which will browse into the modem from the command line.

Message Edited by JMCS on 04-25-2009 10:02 AM
Bronze Star Contributor
anon86290
Posts: 209
Registered: ‎09-02-2003

Re: Three Modem Questions

Hi,

I knew someone would ask, but I don't want to stray from my original question.  I'm using it temporarily as I rework the topology of my home network.  It is not a permanent fixture.

Connection Expert
JamesR
Posts: 6,438
Registered: ‎09-29-2007

Re: Three Modem Questions

Don't have a Scientific Atlanta to plat\y with but that Long Mac address looks like a concatenation of four mac addresses where there should be a space after every 12th hex digit.

Again don't have a SA but usually when you have two public addresses, one of them is the local address assigned to your pc and the other is the "Default Gateway"

 

Bronze Star Contributor
anon86290
Posts: 209
Registered: ‎09-02-2003

Re: Three Modem Questions

That's sort of what I was thinking, but I'll be darned if I can figure it out.  Think I'll take the hub out of the equation (in case that has something to do with it, but I doubt it) and connect the pc directly to the modem.

Thanks.

Connection Expert
EG
Posts: 44,219
Registered: ‎12-24-2003

Re: Three Modem Questions

Are you actually having any connectivity issues ?

 

If not, I wouldn't worry about any of this.

Bronze Star Contributor
anon86290
Posts: 209
Registered: ‎09-02-2003

Re: Three Modem Questions

[ Edited ]

Nope, no connection issues.  I'm just trying to get a deeper understanding of networking/networking devices before I change topologies.  What I have now works fine (because I can follow setup instructions), but there are better ways configure my setup that aren't described in most 'quick setup' procedures.  While investigating other setups, I came across many things I didn't understand, which I want to understand.  Call me a n a l.  As my son would say, hehe.

Thanks.

Message Edited by anon86290 on 04-25-2009 02:55 PM
Connection Expert
EG
Posts: 44,219
Registered: ‎12-24-2003

Re: Three Modem Questions

[ Edited ]

O/k.

 

Please feel free to post back here with any home networking configuration/"topology" :smileywink: concerns that you may have as I'm certain someone will come along to help you out. :smileyhappy:

Message Edited by EG on 04-25-2009 07:35 PM
Email Expert
Posts: 18,241
Registered: ‎04-27-2004

Re: Three Modem Questions

1) If you want to see the modem's MAC address from your PC, first ping the modem with "ping 192.168.100.1" or connect to its web interface.  Then use "arp -a" and look for the row with 192.168.100.1.

 

2) Could you repost the status page without messing up the formatting? Use the forum's "Insert code" tool.

 

3) I'm surprised the modem has a public IP at all. The LAN interface is always 192.168.100.1, and I thought they used 10.x.x.x addresses to access the WAN interface from the Comcast NOC (my Linksys modem doesn't let display the IP address in the status page). In any case, Comcast typically has multiple subnets on each node, due to subscriber growth. So there's no reason why the modem's address has to be in the same address range as your PC.

Networking Expert
kevj
Posts: 4,859
Registered: ‎10-03-2003

Re: Three Modem Questions

[ Edited ]

In the interests of fostering your self admitted compulsive behavior... :smileyhappy:

 

you might look here for the answer to question 1...unfortunately Barmars fine suggestion doesn't work, because of the technical explanation inthe link above....FWIW, it's the first thig I tried too, both from my PC and from the command line of my router....

The guy that maintains that page appears to know a lot about cable modems...in fact, I think he was one of the earliest distributors of some SNMP software to grab data and diags off cable modems, before the ISPs disabled SNMP on them.... :smileysad:

 

It sounds like if you add an additional IP to your PC's NIC, in the same subnet as the cable modem's IP (192.168.100.0/24) you *should* be able to see it's MAC address by doing an "arp -a" at the windows command line. It shouldn't matter if the hub is there, because the hub should be transparent to layer 2 traffic (where the MAC address resides).

 

ditto Barmar on Q's 2 & 3....

 

 

 

Message Edited by kevj on 04-26-2009 01:48 AM

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I don't work for Comcast...


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- post back if your issue is resolved
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Send feedback to Comcast using the 'feedback' link on this page:
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Networking Expert
kevj
Posts: 4,859
Registered: ‎10-03-2003

Re: Three Modem Questions

[ Edited ]

OK, getting geeky now....just to show the the addition of an IP to the internet facing interface of your PC will allow you to get a MAC address from your modem.....

 

Here is output from my router under normal operation. The vlan1 interface is connected to my modem......

# ifconfig vlan1 vlan1 Link encap:Ethernet HWaddr 00:16:01:59:E9:09 inet addr:68.32.xxx.xxx Bcast:68.32.115.255 Mask:255.255.254.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:27431 errors:0 dropped:0 overruns:0 frame:0 TX packets:2037 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:1550526 (1.4 MiB) TX bytes:711788 (695.1 KiB) # ping 192.168.100.1 PING 192.168.100.1 (192.168.100.1): 56 data bytes 64 bytes from 192.168.100.1: seq=0 ttl=64 time=2.295 ms 64 bytes from 192.168.100.1: seq=1 ttl=64 time=1.618 ms 64 bytes from 192.168.100.1: seq=2 ttl=64 time=1.638 ms # --- 192.168.100.1 ping statistics --- 3 packets transmitted, 3 packets received, 0% packet loss round-trip min/avg/max = 1.618/1.850/2.295 ms # arp -a | grep 100.1 #

 

 

with only the Comcast supplied DHCP supplied address on the vlan1 interface, I can ping the modem, but get no ARP entry for it....

 

so I added an address in the same subnet as the modem to vlan1:1 (same physical interface as vlan1):

 

 

# ifconfig vlan1:1 192.168.100.2 # ifconfig vlan1:1 vlan1:1 Link encap:Ethernet HWaddr 00:16:01:59:E9:09 inet addr:192.168.100.2 Bcast:192.168.100.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 # ping 192.168.100.1 PING 192.168.100.1 (192.168.100.1): 56 data bytes 64 bytes from 192.168.100.1: seq=0 ttl=64 time=3.193 ms 64 bytes from 192.168.100.1: seq=1 ttl=64 time=1.601 ms 64 bytes from 192.168.100.1: seq=2 ttl=64 time=1.584 ms # --- 192.168.100.1 ping statistics --- 3 packets transmitted, 3 packets received, 0% packet loss round-trip min/avg/max = 1.584/2.126/3.193 ms # arp -a | grep 100.1 ? (192.168.100.1) at 00:10:95:FF:FF:FE [ether] on vlan1

 

 

and there is the MAC address for the ethernet port on the modem (at least I assume it is the ethernet port. I will have to check the HFC MAC when I get home)....note that it is different from tha displayed on the modem diags page:

 

 

PC Connectivity: USB: Unattached Ethernet: 100 BaseT USB VendID: 069B MAC Address: 00:11:e3:ba:65:2f

 

but if you do a lookup on the MAC addresses, they are both registered to Thompson (my cable modem manufacturer).

 

So, you can get a MAC address for the modem from your PC, but I'm not sure what use it will be, as under normal circumstances, it will not show up on your internal LAN.

Message Edited by kevj on 04-26-2009 03:00 AM

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I don't work for Comcast...


Help us to help you!!
- respond to requests for info
- post back if your issue is resolved
- mark appropriate posts as solutions


Send feedback to Comcast using the 'feedback' link on this page:
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Connection Expert
EG
Posts: 44,219
Registered: ‎12-24-2003

Re: Three Modem Questions

[ Edited ]

Barmar wrote:

 

3) I'm surprised the modem has a public IP at all. The LAN interface is always 192.168.100.1, and I thought they used 10.x.x.x addresses to access the WAN interface from the Comcast NOC (my Linksys modem doesn't let display the IP address in the status page). In any case, Comcast typically has multiple subnets on each node, due to subscriber growth. So there's no reason why the modem's address has to be in the same address range as your PC.


That 73.xxx address is typical of the addy's used for many of CC's CMTS interfaces. He *may* be reading that addy as a first hop in a trace route and think that that is the addy of his modem ?? We all know that modems don't show up in a trace route.

 

It's not likely that the modem has a public IP addy.

 

At this point I would like to say to the O.P. that the reason I asked you why you were using the hub connected directly to the modem is because, and in case you didn't know it, it wont do you much good that way as the modem will only allow 1 MAC address at a time to be connected to it, so if you try to connect any other devices to the hub, they will not be able to gain internet connectivity.

 

Ain't it amazing how a thread can evolve sometimes.. :smileyshocked: :smileymischief: :smileygrin:

Message Edited by EG on 04-26-2009 10:49 AM
Networking Expert
kevj
Posts: 4,859
Registered: ‎10-03-2003

Re: Three Modem Questions


EG wrote:

 

Ain't it amazing how a thread can evolve sometimes.. :smileyshocked: :smileymischief: :smileygrin:


LOL...especially when you have a slow spell at work at 3am!!!

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I don't work for Comcast...


Help us to help you!!
- respond to requests for info
- post back if your issue is resolved
- mark appropriate posts as solutions


Send feedback to Comcast using the 'feedback' link on this page:
http://www.comcast.com/Corporate/Customers/CustomerGuarantee.html?SCRedirect=true

Connection Expert
EG
Posts: 44,219
Registered: ‎12-24-2003

Re: Three Modem Questions


kevj wrote:

 

LOL...especially when you have a slow spell at work at 3am!!!


HeeHee ! :smileywink: :smileygrin:

 

T'was good info BTW ! :smileyhappy: