Ethernet keeps dropping out, "SYNC Timing Synchronization failure"

[asdasta]

For the last few weeks my ethernet has had intermittent issues where it will be extremely slow or drop out completely.

I'm on the 350mb package and get decent wifi speeds in the house, but the ethernet never seems to go above 90mb and regularly as low as 6 or 7mb.

I've tried so many software and hardware solutions but haven't been able to fix it. I factory reset my Hub 3 router and here's the most recent network log info:

18/11/2024 00:16:29 notice LAN login Success;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

18/11/2024 00:07:19 Warning! RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

18/11/2024 00:07:19 critical SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

18/11/2024 00:07:17 critical Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

18/11/2024 00:06:19 Warning! Lost MDD Timeout;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

18/11/2024 00:06:14 Warning! RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

18/11/2024 00:06:14 critical SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

18/11/2024 00:06:13 Warning! RCS Partial Service;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

18/11/2024 00:06:13 critical SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

If anyone can help me I'd be so grateful. Ideally I'd like a VM engineer to address the issue. Thanks!

[asdasta]

I've included additional network log info below in case it helps, thanks!:

Downstream bonded channels
Channel Frequency (Hz) Power (dBmV) SNR (dB) Modulation Channel ID
1 242750000 5.9 40 256 qam 14
2 138750000 6.5 38 256 qam 1
3 146750000 6.5 38 256 qam 2
4 154750000 6.5 38 256 qam 3

Upstream bonded channels
Channel Frequency (Hz) Power (dBmV) Symbol Rate (ksps) Modulation Channel ID
1 46200007 37.5 5120 64 qam 3
2 23600000 37.5 5120 64 qam 6
3 32600000 37.5 5120 64 qam 5
4 39399981 37.5 5120 64 qam 4
5 53700019 37.5 5120 64 qam 2
6 60300017 37.5 5120 64 qam 1

Upstream bonded channels
Channel Channel Type T1 Timeouts T2 Timeouts T3 Timeouts T4 Timeouts
1 ATDMA 0 0 0 0
2 ATDMA 0 0 0 0
3 ATDMA 0 0 0 0
4 ATDMA 0 0 0 1
5 ATDMA 0 0 0 0
6 ATDMA 0 0 2 0

5 162750000 6.5 40 256 qam 4
6 170750000 6.5 38 256 qam 5
7 178750000 6.5 38 256 qam 6
8 186750000 6.5 38 256 qam 7
9 194750000 6.5 40 256 qam 8
10 202750000 6.5 40 256 qam 9
11 210750000 6.4 38 256 qam 10
12 218750000 6.3 40 256 qam 11
13 226750000 6.3 40 256 qam 12
14 234750000 6 38 256 qam 13
15 250750000 5.8 40 256 qam 15
16 258750000 5.5 40 256 qam 16
17 266750000 5.5 40 256 qam 17
18 274750000 5.3 40 256 qam 18
19 282750000 5.3 40 256 qam 19
20 290750000 5.3 40 256 qam 20
21 298750000 5.5 38 256 qam 21
22 306750000 5.5 40 256 qam 22
23 314750000 5.9 40 256 qam 23
24 322750000 6 40 256 qam 24

Downstream bonded channels
Channel Locked Status RxMER (dB) Pre RS Errors Post RS Errors
1 Locked 40.3 7 0
2 Locked 38.9 172 10389
3 Locked 38.9 128 10038
4 Locked 38.9 126 10778
5 Locked 40.3 125 10349
6 Locked 38.9 156 10591
7 Locked 38.6 122 17296
8 Locked 38.9 163 2448
9 Locked 40.3 162 3239
10 Locked 40.3 95 10658
11 Locked 38.9 108 3541
12 Locked 40.3 98 3813
13 Locked 40.3 122 11931
14 Locked 38.9 134 5921
15 Locked 40.3 11 0
16 Locked 40.3 16 0
17 Locked 40.9 15 0
18 Locked 40.3 18 0
19 Locked 40.3 15 0
20 Locked 40.9 15 0
21 Locked 38.9 9 0
22 Locked 40.9 8 0
23 Locked 40.3 7 0
24 Locked 40.3 7 0

General Configuration
Network access
Allowed
Maximum Number of CPEs
1
Baseline Privacy
Enabled
DOCSIS Mode
Docsis30
Config file
A,.iyewrkldJKDHSUBsgvca69

Primary Downstream Service Flow
SFID 962
Max Traffic Rate 402500089
Max Traffic Burst 42600
Min Traffic Rate 0

Primary Upstream Service Flow
SFID 961
Max Traffic Rate 38500089
Max Traffic Burst 42600
Min Traffic Rate 0
Max Concatenated Burst 42600
Scheduling Type BestEffort

[Tudor · Accepted solution]

Often if you do not get > 90 then it’s down to a bad Ethernet cable, try a new one. Also:

Too many errors, but the figures are accumulative since the hub was last power cycled. So please turn off your hub for a short period, this will reset the counters, then post a new full set of stats after about two hours. This will indicate the current line status. 

[asdasta]

Hi, I power cycled the router about 2 hours ago. The network log hasn't added any data since this entry. Internet has been really poor today, had almost no ethernet at all:

18/11/2024 09:25:55

notice

LAN login Success;CM-MAC=**:**:**:**:**:**;CMTS-MAC=**:**:**:**:**:**;CM-QOS=1.1;CM-VER=3.0;

[asdasta]

UPDATE: my new cat6 ethernet cable just arrived and I got full ethernet 350mb when connected directly to the router with the cable. But when I connect from my desktop to my network switch with this cable the ethernet is still almost non-existent. My network switch is only 4 years old, but it's odd that downstairs works suddenly with a cable.

[asdasta]

UPDATE: My problem was ultimately solved by running a new cat6 ethernet cable from the router to my desktop upstairs. All good now, thanks for the help 🙂

[Tudor]

Glad you fixed it. A lot of cable problems can be diagnosed by a cheap cable tester, available on Amazon and others.