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Old Mar 30, 2013, 09:12 PM   #1
brentg33
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Network issues

new network issue.

My current setup has changed a bit.

Comcast cable coming into the office (recently split between Motorola Modem and Cable box)
Modem connected to a 5th generation Airport Extreme
Connected to the AIrport Extreme, a powerline adapter, an imac, printer, and hard drive

I have, very recently, been getting a double NAT error on my Airport extreme, which causes that modem to go offline
Called Comcast, no help at all

I did notice these errors (strange the date changes to June 1970)....but anyway, the look ominous with the words "Critical" attached to them, but beyond that... i have no clue what it means.
Does seem that the date change and these errors always appear in the modem logs when it disconnects/ i get the double nat error.



I have reset my Airport extreme
re-did settings


Did notice some ipv6 settings that i hadn't noticed before








So guys, i turn to you...

Basically, can you tell if my modem is just flakey and need a new one ( own it/ dont rent)
or is there something going on with this ipv6 stuff?


thanks


brent
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Old Mar 30, 2013, 09:44 PM   #2
Primejimbo
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Screen shot the signal page
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Old Mar 30, 2013, 10:15 PM   #3
brentg33
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thanks

so i posted two.

the one with only 1 upstream channel was taken before i just switched the router to link only ipv6

2nd after with 3

then the last, as i was posting this, modem reset and went back to 1 upstream channel 55 dbmv power level
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Old Mar 30, 2013, 10:16 PM   #4
brentg33
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here is the 3rd one
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Old Mar 30, 2013, 10:17 PM   #5
brentg33
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here is the 3 rd
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Old Mar 30, 2013, 10:53 PM   #6
Knoodles
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My setup is different. Comcast and Motorola Surfboard.

http://forums.macrumors.com/attachme...1&d=1364698287

http://forums.macrumors.com/attachme...1&d=1364698287
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Old Mar 30, 2013, 11:10 PM   #7
brentg33
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ok, so im thinking its the splitter.

here is the issue though. i do need the cable line split in the office, as i have a cable box in there as well.

but after removing the splitter, i see the upstream power is at a better level then the 55 before/ with splitter.

as well as the downstream power

and no modem reboots...yet

the splitter is a 5-1000 Mhz
and each split is -3.5db

do they make ones that do not amp the signal at all or less than 3.5db ...


however, i do need a split in the office as i have a HD cable box attached to the imac via eye tv.....any suggestions?
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Old Mar 31, 2013, 09:16 AM   #8
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Quote:
Originally Posted by brentg33 View Post
ok, so im thinking its the splitter.

here is the issue though. i do need the cable line split in the office, as i have a cable box in there as well.

but after removing the splitter, i see the upstream power is at a better level then the 55 before/ with splitter.

as well as the downstream power

and no modem reboots...yet

the splitter is a 5-1000 Mhz
and each split is -3.5db

do they make ones that do not amp the signal at all or less than 3.5db ...


however, i do need a split in the office as i have a HD cable box attached to the imac via eye tv.....any suggestions?
From what you have posted so far, it looks to me like with the splitter in the picture it makes your signal levels too low. That first set of screen shots with -11 signal levels is not going to work well, and that is what is causing the T3/T4 timeout errors. What those errors are is the cable plant sends out a signal (sort of like a ping) to make sure the cable modem is alive, and if the cable plant cannot properly talk to the modem you see those errors in the log. One T3/T4 once in a while is normal, but a string of them like you have is a bad connection.

This is made worse by the way Motorola's cable modem firmware works. If it detects a series of those T3/T4 errors, the modem will reboot on its own.

You are likely seeing the double NAT error on the AE just briefly after the cable modem reboots, then it goes away.... yes? That is what mine does.

Bottom line is with that splitter in your signal levels are too low and you are going to have a bad time.

What kind of coax cable and splitter are you using? You want a good quality splitter and good RG6 cables all the way in.

I would just call Comcast and show them these logs and explain what is happening. They can bump up the signal level coming into your building to fix this. There is also a device called a TAP they can use rather than a splitter that has lower signal loss on one port than the other (splitter divides the loss equally).

I feel your pain. I went around and around with TW Cable for two months with these issues before they finally fixed the signal levels on my street.
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Old Mar 31, 2013, 10:34 AM   #9
brentg33
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thanks for you reply. So the signal is too weak when split? that does seem to make more sense than what i thought. Can i get a TAP and install myself? if so, is there a particular kind? or is it best to have comcast come out?

thanks
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Old Mar 31, 2013, 10:52 AM   #10
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Originally Posted by brentg33 View Post
thanks for you reply. So the signal is too weak when split? that does seem to make more sense than what i thought. Can i get a TAP and install myself? if so, is there a particular kind? or is it best to have comcast come out?

thanks
Something like this would work. You would connect the TAP side on the left to the cable modem with a 1db loss, then the TV to the non-TAP side with a 6db loss.

Here is the thing. Your signal levels are already borderline even with NO splitter. So you are going to be sending a really low signal to your cable box with the TAP and that can also cause troubles.

If it was me, I would make Comcast come out and bump up the signal levels.

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Old Mar 31, 2013, 12:33 PM   #11
Knoodles
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I have my incoming cable split 8 ways and started to have trouble with signal strength. Comcast came out and installed one of these subscriber amps. You can do it yourself.

SVI-Subscriber-Amplifier
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Old Mar 31, 2013, 02:24 PM   #12
brentg33
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Thanks. So I just call comcast and say my signal is low and need a service tech to come out?
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Old Mar 31, 2013, 02:31 PM   #13
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Thanks. So I just call comcast and say my signal is low and need a service tech to come out?
No... because right now without that splitter in there your signal level is within specs. They can see your signal levels from their computer when you call. So they are going to pull that up when you call in and say... "Nope looks good from here."

I would put the splitter back on just before you call, and tell then the modem keeps dropping the connection and you can cure it by taking off the splitter. That way they can see for themselves that the levels are low. Just insist they send a tech out to fix this and they should.
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Old Mar 31, 2013, 02:43 PM   #14
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They charged me a $50 service call plus $40 for the amp. If I had known I could get the amp on Amazon for less than $30 I would have done the job myself.
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Old Mar 31, 2013, 03:07 PM   #15
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They charged me a $50 service call plus $40 for the amp. If I had known I could get the amp on Amazon for less than $30 I would have done the job myself.
I could see you having signal issues with eight devices, but they should be able to get a good enough signal to the OPs house to run two devices without an amp.
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Old Mar 31, 2013, 03:46 PM   #16
Knoodles
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I could see you having signal issues with eight devices, but they should be able to get a good enough signal to the OPs house to run two devices without an amp.
You'd think right? My problem started when trying to watch On Demand on two TV's at the same time. Comcast techs (took two of them) came out with their computer and meters, checked the feed from the pole to the house and pretty much everything inside. They were here for almost two hours. Result... borderline signal strength like OP. The only fix was an amp. No more problems.

I don't understand how they can get a stronger signal without the amp if it isn't there to begin with. Maybe a higher quality splitter will help?

Anyway OP, no service call, no inconvenience, $30, problem solved.
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Old Mar 31, 2013, 03:52 PM   #17
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There are amps upstream where they can crank up the signal for an entire neighborhood.
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Old Mar 31, 2013, 03:58 PM   #18
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Where exactly is the amp installed? Right at the split u need ? Or coming into the house?
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Old Mar 31, 2013, 04:05 PM   #19
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Network issues

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Originally Posted by brentg33 View Post
Where exactly is the amp installed? Right at the split u need ? Or coming into the house?
Not at the house or the feed near the house. Usually if you wander around your neighborhood you can find an amp every several blocks in one of those big green boxes. Or up on a pole.

Edit: sorry I thought you meant the cable companies amp. You would want your own amp before the splitters as close as you can get to the entry point.
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Old Mar 31, 2013, 04:12 PM   #20
brentg33
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Ok entry point to the house? I'll try to call Comcast tonight
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Old Mar 31, 2013, 04:17 PM   #21
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Ok entry point to the house? I'll try to call Comcast tonight
Yes entry to the house.
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Old Mar 31, 2013, 08:13 PM   #22
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Comcast will be out on tuesday
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Old Mar 31, 2013, 10:32 PM   #23
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Up stream (Power level) is a 55 and down stream was a 11. (something)

You want the up stream below 50 and the down stream between -10 to +10

That 55 is killing you, that is the problem right there.

The signal is split too much (by adding the splitter) so you need a dedicated line to it (2 way splitter off the main line, 1 leg from the 2 way going to the modem, and the other leg going to another splitter feeding all your TV's). Now if that is the only splitter, can be a bad splitter, bad line, or the signal is jacked up at the main line.

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They charged me a $50 service call plus $40 for the amp. If I had known I could get the amp on Amazon for less than $30 I would have done the job myself.
You don't EVER amp a line feeing a modem. Looking at the signal of the modem, an amp will make it way worse. The amps are only for cable boxes, and you need a 2-way amp also for Comcast.

Like I said 2-way used, one leg going to the modem and the other leg going to a splitter, and to the TV's. Now you can have one of the 2-way's feeding a modem, and the other leg feeding a 2-way amp to feed the TV's. I gotten 9 TV's and 1 modem to work no problem without an amp. Also if you have bad lines, an amp will just amplify the bad crap.

Last edited by Primejimbo; Mar 31, 2013 at 10:46 PM.
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Old Apr 3, 2013, 07:57 AM   #24
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ok, now im confused. Tech came yesterday, switched out a three way splitter (which is connected directly to the main line coming in the house) He also changed out some wires/connectors/ and a new two way split in my office (modem and cable box). When we left, the upstream was at 48-49, and everything seemed better. I left for a while. Came home and the upstream was now at 55-57. Ofcorse the modem rebooted, but seemed to be working at 55-57. Later on last night, i removed the two way splitter in the office so that its directly going into just the modem. (cable into house/three way split/modem). It was working when i went to be, upstream was at about 50-51. Woke up this morning, modem rebooted (but powerlevels were at 48-49? was getting t3/t4 errors) rebooted, worked for a few and went back down. At one put this morning, it seemed that the upstream reached back up to 57 (without a splitter in the office) What could be causing these spikes? Could it be the new 3 way the tech installed is bad? Im thinking when i get home, i am going to try to do what was instructed above. I think im going to remove the 3 way. add a two way to the line coming in the house. one to modem, the other to a 3 way for tvs.
or is there something else im missing that is causing these spikes?
I called comcast last night again, they now suggested getting an additional outlet installed?


thanks
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Old Apr 3, 2013, 11:19 AM   #25
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I think im going to remove the 3 way. add a two way to the line coming in the house. one to modem, the other to a 3 way for tvs.
or is there something else im missing that is causing these spikes?
I called comcast last night again, they now suggested getting an additional outlet installed?
This is definitely the better way to go. That way the cable modem signal is only going through one splitter and not two. I would be curious what the signal level is where it enters the house before any splitters. The tech should have checked this first thing.

Focus on the downstream power levels and not so much on the upstream. If the downstream is within spec, the upstream will take care of itself. What happens is if the downstream signal is low the cable modem boosts the upstream power on its own to overcome the poor signal. What is the downstream signal level now?

Part of the fluctuation in signal levels is caused by the weather. The hotter it gets outside the warmer the cables get and resistance goes up all along the line, causing signal levels to drop. The cable co. has gear to compensate for this somewhat, but in my experience the signal level still drops as the day warms.

For example, look at my downstream signal levels in this screen shot (taken at 0800 and 60 degrees). By this afternoon when it hits 86 or so that 2dB downstream will have dropped to -1 or -2dB.

Thumb resize.
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