Trouble shooting to rule out router

[randomName]

Been having T3 time-outs on my cable modem the past week or so. Just want to make sure it isn't coming from, or cause of my router. I've been on the phone several times with my ISP over the past week and the one tech took a long shot "it could be your router" which I highly doubt but I thought I'd ask to see if anyone has ever had their router be the cause of a T3 timeout. There, that's my long shot, hah

I'm having a scheduled maintenance visit this Tuesday morning,

Thanks

 

[ScottW]

T3 timeouts are entirely related to negotiation between the modem and the CMTS. They cannot be caused by a separate router downstream from the modem. Usually they're the result of bad signal levels or interference (signal loss or noise injection), or very rarely a bad modem. On-site (your house), check for bad cable, connectors, amplifiers or splitters. If all that's good, then it is somewhere upstream -- and could be anywhere upstream from the pole all the way back to the CMTS.

A few T3 timeouts are generally not a concern, and often you'll still get your rated speed and have no functional problems. A problem that results in lots of T3's may also degrade your speed, and many modems will reboot themselves after a specific number of consecutive T3's -- meaning you'll periodically lose service entirely while the modem reboots. Symptoms like "degraded speed" or "periodic loss of internet" could be any combination of signal/modem/router issues, but T3 timeouts are 100% modem-to-CMTS and nothing to do with the router.

 

[Deleted member 22229]

Yes 100% what ScottW said. Spot on and accurate.

 

[randomName]

Yeah I kinda figured it had nothing to do with my router. I appreciate your time and replies,

Thanks!

 

[randomName]

Ok, hold the phone. Might just be mere coincidence but I was running a custom script to stop "kernel: nf_conntrack: expectation table full" spamming in my router log

#!/bin/sh
# Purpose: Increase nf_conntrack_expect_max to maximum value
# Author: RamGuy
# ------------------------------------------------------------
echo 4096 > /proc/sys/net/netfilter/nf_conntrack_expect_max
echo 300000 > /proc/sys/net/netfilter/nf_conntrack_max
echo 120 > /proc/sys/net/netfilter/nf_conntrack_generic_timeout
echo 1800 > /proc/sys/net/netfilter/nf_conntrack_tcp_timeout_established
service restart_conntrack

I deleted it and the T3 timeouts have stopped the past 2hrs and my connection feels fine. ???

 

[ScottW]

Ok, hold the phone. Might just be mere coincidence but I was running a custom script to stop "kernel: nf_conntrack: expectation table full" spamming in my router log

#!/bin/sh
# Purpose: Increase nf_conntrack_expect_max to maximum value
# Author: RamGuy
# ------------------------------------------------------------
echo 4096 > /proc/sys/net/netfilter/nf_conntrack_expect_max
echo 300000 > /proc/sys/net/netfilter/nf_conntrack_max
echo 120 > /proc/sys/net/netfilter/nf_conntrack_generic_timeout
echo 1800 > /proc/sys/net/netfilter/nf_conntrack_tcp_timeout_established
service restart_conntrack

I deleted it and the T3 timeouts have stopped the past 2hrs and my connection feels fine. ???

Coincidence. The router has no control over signal levels or negotiation with the CMTS.

 

[Greg72]

What are your signal levels like. Getting the tech to look over their equipment from thr pole to your building is worth it and does not cost. ztaps can go bad, lines can get damaged. If your signals are goos, the T3’s are the norm. There is not one connection out there that does not show a T3 error in their log.

dslreports has a faq on what your signals should be like. Just do not take the forums as the word of God, since the topic drift is really bad over there.

 

[Grisu]

For me for sure there can be a correlation!
The router can influence the modem with bad requests or whatever causing the modem to malfunction too and that will be seen as T3.

 

[Adamm]

For me for sure there can be a correlation!
The router can influence the modem with bad requests or whatever causing the modem to malfunction too and that will be seen as T3.

T3 errors are completely modem related, not router.

T3 ( Ranging Request Retries Exhausted )
Explanation: The cable modem has sent 16 Ranging Request (RNG-REQ) messages without receiving a Ranging Response (RNG-RSP) message in reply from the CMTS. The cable modem is therefore resetting its cable interface and restarting the registration process. This typically is caused by noise on the upstream that causes the loss of MAC-layer messages. Noise could also raise the signal-to-noise ratio (SNR) on the upstream to a point where the cable modem’s power level is insufficient to transmit any messages. If the cable modem cannot raise its upstream transmit power level to a level that allows successful communication within the maximum timeout period, it resets its cable interface and restarts the registration process. This error message is DOCSIS event message is R03.0, Ranging Request.

T3 timeouts result when a Cable Modem, that is locked into the downstream, transmits a Ranging Request(RNG-REQ) to the CMTS(Cable Modem Termination System) and 200 milliseconds passes without the CM receiving a Ranging Response(RNG-RSP) from the CMTS. Indeed, maintaining a PING(Packet InterNet Groper) less than 200ms is important to a healthy DOCSIS network. When 10 T3s occur in succession (a period of 20 seconds passes without the CM receiving a Ranging Response, the CM will cease attempting to communicate with the HFC(Hybrid Fiber Optic Coaxial) network and reset its DOCSIS interface. In this case the RESET statistic on the modem log will increment but not all T3s will cause a reset if communication is restored within 10 T3 periods or 20 seconds. When T3 timeouts occur, but not enough occur in succession to trigger a reset, slow speeds are often a symptom as these timeouts slow down the TCP/IP handshakes necessary to maintain internet connections.

T3 Timeouts are typically caused by Upstream Noise causing Ranging Requests to not be clearly received by the CMTS. T3 problems can often be intermittant in nature as they may be the result of noise originating in any part of the plant that shares the same line card at the CMTS with the subscriber impacted. In fact, T3s can even be caused by noise originating on other neighboring nodes if resources are shared at the headend. Speed issues and intermittant connectivity issues are some of the most common problems encounted on our Trouble Calls.

T3 Timeouts can also be encountered when the plant's noise floor is so severe that the CM cannot overtalk it (SNR is bad and Noise power level is higher than your modem's signal). This can affect a single leg of the plant or even entire nodes. When a high noise floor results in several modems resetting their DOCSIS interface because 10 T3 timeouts have occured in succession, as we covered above, this is referred to as a noise outage. Noise outages frequently occur node-wide and while some may self-clear, many continue until a Plant Maintenence Technician locates and repairs the offending source of noise. This is why we ALL must be vigilant about preventing noise from entering the plant.

Occurrence: Extremely common in the customer homes

Symptom: Will cause intermittent disconnections. If you see couple of them, it is fine. If you quite a few of them consecutively, then it will lead to disconnections.

Example:
2017-6-14, 00:05:06 Critical (3) No Ranging Response received - T3 time-out;CM-MAC=00:11:22:c1:db:09;CMTS-MAC=4c:00:82:ee:bd:62;CM-QOS=1.0;CM-VER=3.0

Fixes:
1. Check for the loose or Bad cables. This is by far most neglected and most common fix.
2. Remove extra splitters in house
3. Buy powered amplifier to boost your upstream power
4. Buy better coaxial cables
5. Call for a technician visit to inspect and fix cables outside and inside home (could be rain damage, fire damage, animal damage, construction damage, etc)

 

[Grisu]

And we have never seen that one system can bring down another causing failures over there.
Only because you cant imagine or clearly see it doesnt mean that it doesnt exist!
These systems are a bit more complex than you want them to have.
And there are influences everywhere, sometimes often by luck they get visible.
Thats because no system is independent and working 100% without failures, there are bugs and some situations are not coverd by soft- and hareware to be handled correctly, this is just by design as they wont occour often and so better to be ignored.

 

[randomName]

I had more than a handful of downstream Pwr (dBmV) levels above 15. I reinstalled a dampener on the barrel (coaxial cable) that a tech gave me a while ago and the downstream power levels dropped to under 9. I called in to my ISP and had them reset the modem again. The conflicting thing that pops into mind is I set my router (the 86U) to Fullcone NAT about a week ago, which isn't officially supported, and I kept getting a spam message in my log, 'nf_conntrack: expectation table full' so I followed some suggestions from a thread https://www.snbforums.com/threads/nf_conntrack-expectation-table-full-and-other-log-oddities.55415/ and inserted the script mentioned above. I want to say that it might of been the dampener barrel that helped but at the same time I deleted the script and then things started looking good. I wonder if I change back to Fullcone, and use that script WITH the dampener barrel attached, if the T3 issues will come up again. I'd hate to get into some issues that would interrupt my service again, hmm.

EDIT: I'm sorry, I just can't pinpoint and remember when the issue seemed to stop and what it was due to, the dampener or removing the script.

EDIT2: Looking at my screen shot of my cable modem log, and my last phone call to my ISP it looks like I was still having T3 issues 2 hours after I had attached the dampener cause the last time I called my ISP was to reset it after I reinstalled the dampener which was around 6pm last night and the last T3 issue was at 19:56:19 which is 7:56pm; phone call to ISP was at 6:11pm for 3 min. I think it was after, that I deleted the script and things got better, but I did reboot the modem after the script removal never after the dampener was installed. Unfortunately I deleted the router log files, oooof!

 

[Deleted member 22229]

Here is what's going on and again has nothing to do with your router.


T3 and T4 timeouts. This means the cable modem has sent ranging requests without receiving a response from the upstream control center (CMTS). Your modem talks to the CMTS with a series of synchronize/acknowledge responses. This process is called ranging. During ranging, the modem sends a response to the CMTS essentially saying "Hey, can you hear me?". If the modem doesn't receive a response back in the specified time frame, it logs the event as a critical T3 timeout. The modem then increases the ranging power (US TX), which is the technical equivalent of raising its voice to the CMTS, again saying "Hey, can you hear me?". If no response is received, the modem logs another T3 timeout. The process repeats until the modem and the CMTS establish communication at an acceptable level. An occasional T3 timeout is normal and not a reason for concern. If you see multiple T3 timeouts in a single day, it's an indication that a less-than-optimal condition exists.

 

[randomName]

Here is what's going on and again has nothing to do with your router.


T3 and T4 timeouts. This means the cable modem has sent ranging requests without receiving a response from the upstream control center (CMTS). Your modem talks to the CMTS with a series of synchronize/acknowledge responses. This process is called ranging. During ranging, the modem sends a response to the CMTS essentially saying "Hey, can you hear me?". If the modem doesn't receive a response back in the specified time frame, it logs the event as a critical T3 timeout. The modem then increases the ranging power (US TX), which is the technical equivalent of raising its voice to the CMTS, again saying "Hey, can you hear me?". If no response is received, the modem logs another T3 timeout. The process repeats until the modem and the CMTS establish communication at an acceptable level. An occasional T3 timeout is normal and not a reason for concern. If you see multiple T3 timeouts in a single day, it's an indication that a less-than-optimal condition exists.

Cool. So it might have been the high power levels on the downstream.

I might try Fullcone again and use that script and if anything happens I'll report back.

Thanks for all the help and replies. Sorry for being so critical as to what it could be. It seems more logical that it's only related to the modem but using Fullcone and that script around the same time as the T3 issues started to appear with bad game lag and streaming interruptions raised some questions and interest.

Thanks again, all!

Cheers

 

[Greg72]

This will help you better understand. If things went awry when you connected that filter, undo it and check all connections for tightness.

The idea way is one incoming line to one filter and the Cable Modem on a -7db tap on a splitter. The most common is a two way splitter with one tap for the modem and the other going to a splitter for all tv’s.

It is common to have a Moca filter at the connection at the structure and then the splitter.

Also make sure that only one connection point is grounded to building earth ground where the structure electrical is outside. It is common to have issues when people connect coax lines to power surge strips that claim to protect from spikes and such. Disconnect the line from any power strips and run directly from a single splitter to the modem where the line enters the structure.

https://www.dslreports.com/faq/cabletech

 

[martinr]

Been having T3 time-outs on my cable modem the past week or so. Just want to make sure it isn't coming from, or cause of my router. I've been on the phone several times with my ISP over the past week and the one tech took a long shot "it could be your router" which I highly doubt but I thought I'd ask to see if anyone has ever had their router be the cause of a T3 timeout. There, that's my long shot, hah

I'm having a scheduled maintenance visit this Tuesday morning,

Thanks

When I first saw your thread, I thought you were having difficulties shooting your router. I figured it was a bit of a drastic way to rule it out.

 

[randomName]

When I first saw your thread, I thought you were having difficulties shooting your router. I figured it was a bit of a drastic way to rule it out.

Well I was told several times that even with downstream power levels above 15 with a good SNR level and no internet issues that things were fine. Then a brilliant phone tech suggested it might be my router so I thought I'd just confirm what I always thought but then some coincidences came up and I dug deep. The dampener helped my downstream power levels but I was still getting T3 errors a couple of hours later. I switched back from Fullcone and removed the script and my internet got better. So doing a bunch of things at once didn't really help solve where the issues were coming from however things seem OK for now. More work is being done in my area with my ISP, and I still might have the tech come by on Tuesday to check things over. I'm still debating trying to recreate the issue with the suspected Fullcone and script although if problems arise it might just be isolated at the router now that I know the downstream power levels are within spec and no T3 trouble shows up. I normally never see T3 issues as an occasional thing.

 

[Makaveli]

As someone that has switched from Cable.

T3 times out are completely Modem and CMTS related as everyone said it has nothing to do with the router.

I use to see them in my cable modem logs.

 

[ScottW]

Well I was told several times that even with downstream power levels above 15 with a good SNR level and no internet issues that things were fine. Then a brilliant phone tech suggested it might be my router so I thought I'd just confirm what I always thought but then some coincidences came up and I dug deep. The dampener helped my downstream power levels but I was still getting T3 errors a couple of hours later. I switched back from Fullcone and removed the script and my internet got better. So doing a bunch of things at once didn't really help solve where the issues were coming from however things seem OK for now. More work is being done in my area with my ISP, and I still might have the tech come by on Tuesday to check things over. I'm still debating trying to recreate the issue with the suspected Fullcone and script although if problems arise it might just be isolated at the router now that I know the downstream power levels are within spec and no T3 trouble shows up. I normally never see T3 issues as an occasional thing.

If DS power is >15, there is a plant/amp WAY out of adjustment and signal is likely distorted, and that's leading to the T3's (your modem probably isn't understanding the cmts responses because they are over-amplified and distorted). Your ISP is the only one that can fix it!

Adding an attenuation device on-site (what I assume you are referring to as dampener) may help, but likely will just lower the already-distorted signal and you're likely to still have issues. Patience and stubbornness is the key -- keep politely but persistently nagging your ISP, keep telling them the DS signal level is out of spec, and EVENTUALLY they will fix the problem.

(Saying this as someone who has "been there and done that" a few times! Very frustrating, but if you hang in there and persist they will eventually fix it.)

 

[Val D.]

I see a few T3 time-out every day in my modem's log. Does not affect the performance. It's been like this forever on 3 different cable modems with 3 different routers connected to them. Never bothered to ask what is causing it because there is actually no problem to solve. Signal levels are good, up/down speed is as expected, no disconnects, no reboots.

 

[randomName]

If DS power is >15, there is a plant/amp WAY out of adjustment and signal is likely distorted, and that's leading to the T3's (your modem probably isn't understanding the cmts responses because they are over-amplified and distorted). Your ISP is the only one that can fix it!

Adding an attenuation device on-site (what I assume you are referring to as dampener) may help, but likely will just lower the already-distorted signal and you're likely to still have issues. Patience and stubbornness is the key -- keep politely but persistently nagging your ISP, keep telling them the DS signal level is out of spec, and EVENTUALLY they will fix the problem.

(Saying this as someone who has "been there and done that" a few times! Very frustrating, but if you hang in there and persist they will eventually fix it.)

I'm not sure if it's the length of the line that determines the signal strength or my location along the line but the attenuation/dampener seems to be the 'hot fix' in place. I'm not sure if it's something that has to be there constantly but it doesn't bother me.

I did re-enable Fullcone Nat with the script and nothing feels wrong like bad game warping, or stuttering in any streaming, so far

At this point I feel I can dismiss the ISP phone tech's suggestion that it might be my router. It might just of been a routine questionnaire that they were following which is more than likely but it doesn't hurt to ask and investigate.

Thanks all for the kind help