Troubleshooting a cable modem

Necronic · May 5, 2013

I've been having some issues with my internet for the last week or so, and I've been killing myself trying to fix it. The speeds should be 30/10 mbps down/up. Right now they jump between 60 and 0.2, usually lower than 10.

Now, the first thing I did was replace my modem/router combo with a simple modem (ubee d3.0). I couldn't get my old wrt54g router to work so I went and bought a new E2500. That was giving inconsistent speeds and disconnecting randomly. I went ahead and connected directly to the modem and got pretty solid/consistent speeds of around 70/10mbps.

I assumed it was the router. So I returned it and grabbed an Asus TR-54 something or other. This is giving me similar wonky speed variations. But still, when I connect straight to the modem it works fine.

This is puzzling. I called comcast up and they said they thought something might be wrong with the line. They went ahead and boosted the signal which kicked up the speeds for a bit, but then they settled back down in their erratic range. They are sending someone out, but I want to be ready for them (so they don't just tell me to turn it on and off again. )

So I jumped onto the modem to pull some data from it, here's what I have so far:

DS-1 DS-2 DS-3 DS-4
Frequency 627000000 615000000 621000000 633000000
Lock Status
(QAM Lock/FEC Sync/MPEG Lock) Y/Y/Y Y/Y/Y Y/Y/Y Y/Y/Y
Channel Id 3 1 2 4
Modulation 256QAM 256QAM 256QAM 256QAM
Symbol Rate
(Msym/sec) 5.360537 5.360537 5.360537 5.360537
Interleave Depth I=32
J=4 I=32
J=4 I=32
J=4 I=32
J=4
Power Level
(dBmV) -2.52 -2.34 -1.77 -2.38
RxMER
(dB) 35.60 30.21 32.50 36.84
Correctable
Codewords 993 172470936 1104 898
Uncorrectable
Codewords 1687 26452595 1404 1449

The power seems good, the SNR seems okish (30-37). But what seems weird are those (un)correctable codewords on DS-2. Now, this is a bonded channel, which I don't really understand, but if that one channel is faulty, would the bonding screw up the whole thing?

Anyways, does this look right to you?

DarkAudit · May 6, 2013

The first thing I'd do... would be to go post on DSLreports.com.

strawman · May 6, 2013

If the one modem worked direct, I'd go to that, and try a few different routers until you found one that worked well.

Bubble181 · May 6, 2013

If the speeds are good directly from modem to pc, I'll still guess it's somewhere in the additional in-betweens. If it's not the router itself, there might be a bad connection that's constantly skipping somewhere in the cable or the plug you use?

DarkAudit said:
The first thing I'd do... would be to go post on DSLreports.com.

See, that's the difference between an Internaut and a Halfie: first thing I'd do is light the PatrThom signal and hope

DarkAudit · May 6, 2013

Bubble181 said:
See, that's the difference between an Internaut and a Halfie: first thing I'd do is light the PatrThom signal and hope

That's what the OP was for.

Bubble181 · May 6, 2013

True enough

PatrThom · May 6, 2013

I've put off answering this because I'm 'fraid I have little to no experience with cable modems/DSL modems/etc. I have a book or two around somewhere (and the Internet, of course), but I've never had to set up my own equipment, enter my own settings, or anything like that. However, if you are consistently getting good speeds when you have connected directly to the modem, then I believe the settings on your cable modem aren't your issue.

I am assuming you've already tried all the obvious stuff to make sure it's not just a bad port, bad cable, that sort of thing. So here's some things to try:
-Make sure the cable company knows the MAC address of your router. Some ISPs will kill your connection if they don't recognize the device that's plugged into it. Give them a call, explain that you just switched your router, and ask if they need to know your new MAC address. Your computer works fine, but they may already have your computer's MAC whitelisted from previous.
-Find out whether or not the cable modem is giving the device plugged into it an IP address in the private range (starts with 192, 10, or 172), and if so, make sure the addresses that the router hands out to all the devices connected downstream from it are not in the same subnet. On a related note, if you are using WiFi, use either the router wifi or the cable modem wifi, but not both. Turn WiFi off on the device you aren't using.
-If your router has more than one LAN port, disable DHCP on your router, and then plug the connection from the cable modem into the LAN side of your router instead of the WAN port. This will transform your router into just a hub/switch. If speeds magically go back up to normal, then you have a routing issue, not a device issue, and you will need to find out what is up with your routing layout.
-There's a chance that the issue is just that you have too many splitters in your cable line. Routing your signal from one main cable line to 4 different cable boxes will cut your signal down quite a bit. If your slowdowns happen when everyone is watching cable (especially digital channels), then that's probably your culprit.

Also, the image link in the OP is broken.

--Patrick

GasBandit · May 6, 2013

Yeah, I also came in here to say make sure your router is using the same MAC address on its "outside" side as your PC's network card, that one's bit me in the butt a couple times... but I see Patr's beat me to the punch as usual.

PatrThom · May 6, 2013

GasBandit said:
that one's bit me in the butt a couple times...

I once spent about 4 and a half hours troubleshooting a router only to find out that was what was up. I started the process by asking the guy, "Did you call the cable company to let them know you have a new router?" and was told, "Yeah." (4-1/2 hrs pass and I get frustrated enough to call the cable company myself) "Do you have this MAC address yet?" "No, hang on while I add it." All fixed. Grrrr.....

--Patrick

Necronic · May 6, 2013

I'm pretty sure I have the MAC address handled. I plugged my laptop into the modem for a bit, then switched over to the router and had it clone the PC's MAC address. I think that sorted it.

DarkAudit · May 6, 2013

PatrThom said:
I once spent about 4 and a half hours troubleshooting a router only to find out that was what was up. I started the process by asking the guy, "Did you call the cable company to let them know you have a new router?" and was told, "Yeah." (4-1/2 hrs pass and I get frustrated enough to call the cable company myself) "Do you have this MAC address yet?" "No, hang on while I add it." All fixed. Grrrr.....

I don't recall ever having to call the cable company to inform them of a new router. I guess I'm just fortunate that way. *shrug*

PatrThom · May 6, 2013

Some devices work fine, others are spotty or don't work at all, MAC filtering is usually the first thing to check, there.

--Patrick