Netgear model C7000v2 Cable Modem Router Log Questions

[kyledani]

I have the Netgear C7000v2 modem router. I have had this modem connected to xfinity service for awhile now. I am getting some log entries for my modem that I haven't been able to resolve. The first is this message in the log "

1970-1-1, 00:00:38

Critical (3)

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=10:0c:6b:08:4b:28;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;

and the second is this message in the log"

1970-1-1, 00:00:46

Critical (3)

No Ranging Response received - T3 time-out;CM-MAC=10:0c:6b:08:4b:28;CMTS-MAC=00:6c:bc:b9:51:61;CM-QOS=1.0;CM-VER=3.0;

Your assistance with this would be much appreciated. Thanks

[EG]

Are you experiencing any actual connectivity problems or are you just focusing on the error log entries ?

[kyledani]

I do get random connectivity drops. As far as the drops are concerned, there isn't a pattern to them. Under the routers event logs I have it set to report DNS attacks. The interesting thing about those log hits is that often times they do result in connection drops. They most consist of DNS floods and port scans. I have read up on those particular events and everything that I can find say that they are normal to see in your router logs if you have the router setup to log "Known DoS attacks and Port Scans". Almost all of those logged attacks have a source IP address of the DNS server that I have configured and the target is usually the Comcast public DHCP address assigned to the Internet port of the router. Thoughts?

[EG]

What do the modem's signal stats look like ? 

Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.

[kyledani]

On the downstream it ranges from the best being -10.5dBmV to the worst being -12.3dBmV. On the upstream the power ranges from a low of 51.5 to 53dBmV. As for the SnR the low is 36dB and the high is 37.9dB. I think these power and SnR values are the source of my problem!? Thoughts?

[EG]

The downstream power is weak and the upstream power is too high and it may be intermittently fluctuating even higher to out of spec levels. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, and latency problems.

In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed, and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.