cable-modem interview questions
Top cable-modem frequently asked interview questions
I'm tired of renting my cable modem and am wondering how to tell them apart.
Some are 1/2 the price of others yet they all seem the same. What are the criteria one should look for when purchasing a cable modem.
Source: (StackOverflow)
I live in an apartment building in Czech Republic, Europe. I have a cable internet connection with a static IP connected to an Ubuntu server I set up. Recently out building lost power, though the elevators and emergency lights continues functioning on some secondary emergency power supply.
I was thinking of buying an UPS unit to keep my cable modem, router, and MiniITX Ubuntu server running during a power outage. I know that when I lived in the US, telephone(edit-removed: /DSL) connections will continue to function because they have their own power source.
So, if I hooked up a UPS, would my connection remain alive? Or do cable internet connections rely on repeaters/signal boosters/etc. which use the local power source?
Source: (StackOverflow)
I'm trying to help a friend remotely with an internet connectivity problem. His internet went down this morning and the cable company had him switch to a Motorola Surfboard SB6141 modem from an older model Surfboard. It seems to be struggling to acquire a DHCP lease. On either of his Macs, when hooked up directly, it typically seems to take trying to force the computer to acquire a DHCP lease several times before it finally works. Mysteriously, however, when we hook the SB6141 up to a router even multiple attempts to renew the lease never leads to the router acquiring the lease (and this was true with his original Linksys WRT54G, a new Linksys E1200 and a new Linksys E2500). The routers consistently report an IP address of 0.0.0.0 (i.e., they haven't received any DHCP information).
Since the latter two routers were brand new, I don't think the router could be at fault and, normally, I've found that this sort of setup is a straightforward one that doesn't require any odd settings. Is there anything peculiar about the SB6141 that might be interfering with a normal router configuration? I'm wondering if the fact that the DHCP process seems less than smooth when directly connected to the computer indicates that there is something amiss with Charter's DHCP server.
UPDATE: To clarify, the routers are routers with all of the settings set to the OEM's factory settings. Normally, in such a case, the router would seemingly just start working with a cable modem and pick up a DHCP lease, which is what is puzzling here.
Source: (StackOverflow)
I am selling my old docsis cable modem, and my buyers' frequently asked question is "is it not stolen/blacklisted?"
Will I have problems if I post the modem's MAC addresses on my online ad? I mean will a hacker be able to get it banned or void my modem or spoil my sale with this information?
Source: (StackOverflow)
That's what Charter asked me to do. Until last week, I didn't have any problem with my Zoom cable modem. But last week, my 20Mbps cable modem was checked to 1Mbps according speedtest.net. So I contacted Charter Comm. and at the time, they said to me that they are fixing something. But after a week, it's still 3Mbps so I contacted their CS again.
Long story short, this time the agent said I need to buy a new modem complying DOCSIS 3.0. Because of the provision they added, he said, I am having 3Mbps now. According to the agent, provisioned speed is conflicted with my modem under 12Mbps, and becomes dominant over actual speed. Suppressing all the emotions going through my head, does that advice make any sense? Why would a modem, working fine before, become so slow with provision change?
Buying a new modem does not really matter but I am afraid that it may not fix the suddenly slow internet speed. Any advice would be appreciated.
UPDATE: I bought Motorola SB6120 SURFboard today and wasted a couple of hours to adjust my router, which is totally my fault as this is my first time to do that. But Charter's agent was right as my internet speed is 20Mbps right now. I am all happy now. Thanks for your responses, guys.
Source: (StackOverflow)
I purchased a modem from someone on craigslist to use for my new cable internet service. The modem appeared to be unused and in brand new condition. However, the sticker on the box with the modem's serial number and MAC address was removed.
I first tried using the internet a few hours after the technician activated the service. I immediately noticed my download speeds were slow. Running a speed test, I see that my download speeds are less than 1Mbps (my service level is for 50 Mbps). My upload speed seems to be fine.
My guess is that some previous owner of the modem has used the serial number and MAC address to clone my modem. When I activated my internet service, they were able to be provisioned on the network under my account. Now they are downloading massive amounts and using up all of my allocated bandwidth. Is this feasible? If this is true, is there anything I can do?
Source: (StackOverflow)
Yesterday (Friday, September 21, 2012), my Internet connection started acting up. After some testing, I confirmed a very specific and baffling set of symptoms:
- Internet connection goes away every 25-35 minutes (I did not confirm the exact interval, but it seems to be about 30 mins.)
- Only some protocols are affected; HTTP*, P2P, etc. stop working; FTP, etc. continue to work
- When it’s stopped, cannot even ping router or cable-modem IPs or view their firmware pages
- Domain-names and IPs are irrelevant (for protocols that stop working, neither work, for those that still work, both work)
- Resetting router fixes it for another 30 minutes
- Keeping the connection idle or active doesn’t seem to make a difference (nor the bandwidth usage in that period)
- Connecting directly to cable-modem allows it to work indefinitely
- Disconnecting the router from the cable-modem works indefinitely (no Internet connection obviously, but can still access router IP and firmware page)
- Connecting the router to the cable-modem, but putting the modem on standby also works indefinitely
- Same problem with both a wireless laptop and wired (on any port) desktop (both Windows 7; will try to test Windows XP when possible)
- Nothing had changed in the days leading up to the issue. No modifications to the networking configuration or the router; there were not even any Windows updates except for an MSSE definition update.
- Waiting does not fix it, nor does any amount of fiddling with anything; only resetting the router fixes it for 30 minutes (resetting the cable-modem doesn't work either)
- If I keep pressing the standby button on the cablemodem after browsing some pages, the connection works indefinitely (If I press the button to restore the connection, browse some pages, press the button again to cut the connection, it works fine for hours and hours without issue. Only when I leave it active for a while does it finally stop. I repeated this for three days with the same results.)
I tried cleaning the pins in the router’s plugs, but that didn’t help, which was not really a surprise since I was not getting a lost connection error.
Obviously my first thought was that the router was having a problem, and this is borne out by some tests. The problem is that when it drops, it is not a full drop since I can still do things like ftp ftp.mcafee.com and such which means that the connection and DNS are still working. Moreover, if it were the router, then why does it stay alive indefinitely when not connected to the cable-modem (i.e., no outside influence)?
The problem doesn't seem to be either the cable-modem nor the router, but rather an interaction between the two, like something from the outside (port scan? hacker? ISP?) that is triggering a problem in the router. I see that there have been a couple of vulnerabilities for the DI-524, but those were a while back and should be fixed since I have the last firmware for it.
I don’t think it’s my ISP (Rogers) since I have been using the router for several years without problem and can connect indefinitely when bypassing it. But I can’t rule them out since that is one of the only possible things that could have suddenly changed.
Does anybody have any ideas of explanations, fixed, or tests?
(I note that when I opened the router, I heard a very high-pitched noise from somewhere near the capacitors/ferrite ring which I don’t think I heard the last time I opened it a few years ago, but then if it were that, then why would it affect only a very small, specific set of functions?)
Update
Last week, my Internet connection dropped out for two days. I called the ISP and they had me bring the cable-modem in to be replaced. I exchanged the SB5100 for a new cable-modem that has a built-in router with wireless AP and firewall. (I left it in gateway mode instead of bridge mode.)
This morning it started behaving just like the old router. Most protocols continued to work (mail, P2P, NTP, etc.) but web-browsing (HTTP) was dead; I could not even connect to the cable-router’s web-interface. I rebooted the cable-router and HTTP functionality was restored; exactly like the previous router.
I find it highly unlikely that this could be a coincidence or related to the router itself since the new one is literally brand-spanking-new (bagged, twist-ties, in a box, with that new-plastic smell, etc.), and completely different from the old one (the new one is an ISP-branded model labeled “Hitron” while the old one was a D-Link DI-524).
Source: (StackOverflow)
I'm using HomePlug AV2 600 devices to connect upstairs with downstairs (router is downstairs). A check with iperf shows bandwidth of ~100Mbps, and data transferred on the local network from downstairs to upstairs is transferred at about that speed. Good times.
But when I try to access the Internet from upstairs, maximum throughput is only 40Mbps. Bad times.
If I try from downstairs, I get the full 80Mbps that my Internet connection allows. This is really puzzling, as I know the HomePlugs are working faster than that for local data.
Here's what my setup looks like (the router is connecting to a fibre modem using PPPoE, everything has gigabit ports, and all testing was using wired connections):
+----+
| PC |
+-+--+
|
|
+---+----+ +----------+
| Switch +---------+ HomePlug |
+--------+ +-----+----+
|
Upstairs |
+-------------------------------------------------------+
Downstairs |
|
+-------+ PPPoE +-----------------+ +-----+----+
| Modem +-------+ Wireless Router +-----+ HomePlug |
+-------+ +-----------------+ +----------+
If I connect to the router downstairs (wired), then it works great:
+--------+ +----------+
| Switch +---------+ HomePlug |
+--------+ +-----+----+
|
Upstairs |
+-------------------------------------------------------+
Downstairs |
|
+-------+ PPPoE +-----------------+ +-----+----+
| Modem +-------+ Wireless Router +-----+ HomePlug |
+-------+ +-----------------+ +----------+
|
|
+--+-+
| PC |
+----+
If I wire the downstairs HomePlug straight to the modem, and setup a PPPoE connection from the Windows 7 machine upstairs, it also works as expected:
+----+
| PC |
+-+--+
|
|
+---+----+ +----------+
| Switch +---------+ HomePlug |
+--------+ +-----+----+
|
Upstairs |
+-------------------------------------------------------+
Downstairs |
|
+-------+ PPPoE +-----+----+
| Modem +-------------------------------+ HomePlug |
+-------+ +----------+
I've also tried plugging the HomePlugs in right next to each other on the same floor, and get the same poor results:
Downstairs
+-------+ PPPoE +-----------------+ +----------+
| Modem +-------+ Wireless Router +-----+ HomePlug |
+-------+ +-----------------+ +-----+----+
|
|
+----+ +-----+----+
| PC +-----+ HomePlug |
+----+ +-----+----+
So the issue is only there when connecting to the Internet through both HomePlugs and the router, and only affects WAN traffic. I've tried replacing the router with a newer model, but get the same result. I also tried replacing the HomePlugs with a different brand (first tried Solwise, now Devolo).
I've also tried creating a PPTP VPN tunnel between my upstairs computer and the downstairs router - and this does inexplicably gives me the full bandwidth I would expect. But this relies on using DD-WRT on my router - and it's very flakey.
I'm at a loss, so any help would be much appreciated!
Source: (StackOverflow)
I have reinstalled Windows XP and posted about not being able to connect to the internet. I did go and ensure all drivers are there.
Now, when I type ipconfig /all, I get
- a physical address
- DHCP enabled
- autoconfiguration enabled
- autoconfiguration IP address
- subnet mask
- a line that says default gateway
where default gateway is the only line with no numbers or anything next to it.
My wireless connection works, but how can I get this ethernet connection to work? This was working prior to this fresh reinstall.
Source: (StackOverflow)
The cable technician installed my cable modem today, but brought the wrong adapter. He managed to force it into the modem, but I looked at the ratings and the modem says 12V 1.5A while the adapter says 12V 1.25A.
It's working, but could this damage the modem?
Source: (StackOverflow)
I have a Motorola SB6120 cable modem that I bought last November or December. It's been working great since I got it. I have the cable modem connected to an APC surge protector and turn the surge protector off at night to save a few pennies on electricity. About 2 weeks ago on a Thursday morning when my wife turned everything back on, there was no Internet. Stayed down all day, I played with it when I got home, and I ended up scheduling an service call for the following Saturday. Later that night, I got creative, reset the cable modem to the factory defaults, left it off for about half an hour, and when I turned it back on - Internet!
We were fine until the following Thursday (Thursday thing is weird too) then the exact same scenario. Didn't come up in the morning, stayed down all day, but this time even after trying similar tricks from previous outage, nothing got us back online. Waited to Friday morning to see what would happen over night, and after still nothing scheduled service call for following Monday. By the way, no internet all weekend - really sucks!
On Monday, tech comes out, says signal is weak, thinks cable is damaged where neighbor behind us put in fence last year. On Tuesday, repair crew comes out and does something out by fence, but still no internet. Tech comes out later that afternoon, is able to get cable company's modem online (Scientific American) but my modem won't.
I ended up calling Motorola support, and I learn the power levels the modem is reporting are too low. Upstream power is 0, signal to noise ratio in the low 20s. So he says the signal strength is too low. I start paying closer attention after that and begin to notice a pattern. When I first turn on the modem, it reports good signal strength: signal to noise of 37, downstream power of 3, upstream power of 49. But after 10-15 minutes, signal to noise drop to low 20s and upstream drops to 0.
So now I'm not sure what to do. Call the cable company and demand they fix the frickin' line? Or call Motorola and insist they RMA the modem? I don't have a way to test my modem elsewhere, so I can't really verify it's still good. Cable company says signal must be fine if their modem will connect. I've also verified they have the right mac address.
Source: (StackOverflow)
After a while (can be days, can be weeks), my network access speed slows down to ~2Mbps. Power cycling the modem (router and modem power off, then modem on, then router on) improves the performance to about 15Mbps. I'm curious what is the underlying reason for the slowdown...
Edit: Router and modem are both Linksys (CM100 and WRT320N), the OS is Windows 7. Provider is Comcast. I've had the same symptoms with the old hardware (Microsoft router, and rented RCA modem). If you search for "power cycling" you can find a lot of articles, speculating if it helps or not. In my case it clearly helps - but why?
Source: (StackOverflow)
There is a private forum site that I have accessed without issue for a long time. As of about 2 weeks ago, without warning, I suddenly cannot access the site through any browser.
My first assumption was that the site was simply taken down. Out of curiosity, a few days ago I accessed a proxy avoidance server and typed in the site's address. It loaded the page without error.
So my second assumption was that the forum administrator was blocking me. Using the proxy, I was able to log in using my name and password, no problem, which halfway disproved this second theory as I would imagine they would have deleted my account in that case.
I posted on a help board within the forum, asking if I had been punished or banned from the boards. I received a response from the administrator that no such thing had happened and he couldn't explain what was going on.
Now my last guess is that it is ISP-related. I am with Comcast (not by choice), and have been for 2 years. Over the last 2 years I've accessed the site without any problems. Suddenly it is blocked.
I thought about changing some settings in the wireless router or cable modem through which I connect, but I wouldn't know what to change or how. Would this even help?
What/Who else would be able to block my access to a particular website?
Source: (StackOverflow)
I am curious if I were to move, do you have to tell your ISP, in this case my cable company, that I am moving? Is the cable modem MAC restricted to a certain CMTS, or could I use any CMTS belonging to my ISP?
EDIT: I am interested in whether or not by virtue of me having internet service through a specific ISP, if my cable modem can connect to any CMTS my ISP has, or if I am restricted to just a one (or a subset). If I were to take my cable modem to a friend's house who has cable service through that same ISP (or no service at all, but at least having a cable into his house from that company), would it be able to get service at that location also using my cable modem?
Source: (StackOverflow)
We have Comcast cable internet, and we want to connect two devices: one WiFi router, and one PC via a wired connection. We have these all set up in the same room and it basically works:
wall --coax--> cable modem --cat5--> (WAN) wifi router (LAN) --cat5--> PC
(The modem is an Arris TM822G DOCSIS 3.0 model that also provides phone service).
Unfortunately, though, the wifi signal doesn't reach to the back of the house. We do have another cable outlet at that end, though, so we're contemplating using MoCA to run ethernet over the cable setup. We got an Actiontec ECB2500CK01 two-adaptor MoCA kit and, following the instructions and some internet forum advice, set it up as follows:
wall #1 --coax--> splitter --coax--> cable modem <-------
^ |
| cat5
| |
---coax--- MoCA adaptor #1 <---
(This is already confusing to somebody who's only used to twisted-pair, as both the WAN connection to the cable modem and the LAN connection from the MoCA adaptor are apparently supposed to travel over the same coax cable, but I guess that's the magic of RF.)
Theoretically, in the other room we would then set up:
wall #2 --coax--> MoCA adaptor #2 --cat5--> wifi router
However, before getting this far, we realized there was a problem: neither the cable modem nor MoCA adaptor #1 have a free Ethernet port, so there's no place to plug in the wired PC.
Now, there is a third cable outlet elsewhere in the house, so theoretically we could get a third MoCA adaptor and plug both it and the cable modem into that outlet, while using MoCA adaptor #1 just to hook up the PC. However, that's another $80-$100 down the drain plus it seems stupid.
On the other hand, I might have a wired router at the bottom of a box somewhere, in which case this seems like it might work, in theory:
wall #1 --coax--> splitter --coax--> cable modem <------
^ |
| cat5
| |
| (WAN)
| wired router
| (LAN) --cat5--> PC
| |
| cat5
| |
---coax--- MoCA adaptor #1 <--
Should this work? Is the MoCA adaptor smart enough to just route LAN traffic? Am I likely to run into trouble with Comcast expecting the router to have a certain MAC address, or any of that sort of nonsense? If I'd be better off just running 50' of cat5 under the floorboards, I'd rather find that out before I go any farther down the MoCA route.
Source: (StackOverflow)