Asus RT-AX86U dropping WAN connection to Arris S33

[Llimona]

Greetings, I've got a new Asus RT-AX86U (Merlin 386.7) connected to an Arris Surfboard S33 cable modem using the 2.5G port on the router as the WAN port and the modem's 2.5G port. My ISP/plan is Comcast's Xfinity Gigabit (1200mbps down/35mbps up).

The internet connection seems to drop a few times a day for about a minute. Looking at the Asus logs I see something similar to the following whenever it happens:

Jul 10 21:22:57 kernel: NOTE: Using Port Grouping for IMP ports : [ 0 --> 4 ] [ 1, 2 --> 5 ] [ 3, 7 --> 8 ]
Jul 10 21:22:57 kernel: eth0 (Int switch port: 3) (Logical Port: 3) (phyId: 1e) Link DOWN.
Jul 10 21:23:03 WAN_Connection: WAN(0) link down.
Jul 10 21:23:38 kernel: NOTE: Using Port Grouping for IMP ports : [ 0 --> 4 ] [ 1, 2, 3 --> 5 ] [ 7 --> 8 ]
Jul 10 21:23:38 kernel: eth0 (Int switch port: 3) (Logical Port: 3) (phyId: 1e) Link Up at 2500 mbps full duplex
Jul 10 21:23:38 WAN_Connection: WAN(0) link up.
Jul 10 21:23:38 rc_service: wanduck 1428:notify_rc restart_wan_if 0
Jul 10 21:23:41 wan: finish adding multi routes
Jul 10 21:23:42 miniupnpd[12156]: shutting down MiniUPnPd
Jul 10 21:23:43 WAN_Connection: WAN was restored.
Jul 10 21:23:47 miniupnpd[18375]: HTTP listening on port 52330
Jul 10 21:23:47 miniupnpd[18375]: Listening for NAT-PMP/PCP traffic on port 5351
Jul 10 21:23:47 rc_service: udhcpc_wan 18260:notify_rc stop_samba
Jul 10 21:23:47 rc_service: udhcpc_wan 18260:notify_rc start_samba
Jul 10 21:23:47 rc_service: waitting "stop_samba" via udhcpc_wan ...
Jul 10 21:23:47 wsdd2[12180]: Terminated received.
Jul 10 21:23:47 Samba_Server: smb daemon is stopped
Jul 10 21:23:48 dhcp_client: bound 192.168.100.10/255.255.255.0 via 192.168.100.1 for 30 seconds.
Jul 10 21:23:48 Samba_Server: daemon is started

This is at a new house with new equipment so I don't have a previously reliable setup to go back to.

Things I tried:
- Replacing the short ethernet cable between the modem and router. Made no difference.

Things I can still try (but that aren't good long term solutions):
- Bring an older router into the mix for a temporary test to rule out the router as a culprit.
- Attempt to use the 1G WAN port instead of the 2.5G port.

Would someone have a suggestion on how to investigate this further?

Thank you!

 

[geobernd]

Take a look at the logs on the S33:
If there is a Comcast line issue (e.g. excessive T3/T4 timeouts) the modem will reboot and you will see link down/up messages...
We should be able to help interpret here or in the Comcast/Xfinity forum at dslreports https://www.dslreports.com/forum/comcast if that is the case

 

[Llimona]

The S33 logs are pretty hard to read for me as the timestamps are all over the place. But the fact that the clock is getting reset hints at the modem indeed resetting itself.

For example, last WAN drop reported by the Asus was at 6:42. Logged in at 8 AM in the S33 and found this:

31/12/1969
16:00:19    3    SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=ac:db:48:bd:36:c9;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
10/7/2022
06:54:53    3    SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=ac:db:48:bd:36:c9;CMTS-MAC=00:90:f0:27:05:00;CM-QOS=1.1;CM-VER=3.1;
31/12/1969
16:00:19    3    SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=ac:db:48:bd:36:c9;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
31/12/1969
16:00:15    3    CMSTATUS:US_Diplexer_Mode_Change:Init, 5-42MHz.
31/12/1969
16:00:19    3    SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=ac:db:48:bd:36:c9;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
31/12/1969
16:00:21    3    CMSTATUS:DS_Diplexer_Mode_Change_Ignored:TLV-21.2, 258MHz.
31/12/1969
16:00:21    3    CMSTATUS:DS_Diplexer_Mode_Change_Ignored:TLV-21.3, 1002MHz.
31/12/1969
16:00:21    3    CMSTATUS:US_Diplexer_Mode_Change_Ignored:TLV-21.1, 42MHz.
31/12/1969
16:00:34    3    CMSTATUS:DS_Diplexer_Mode_Change_Ignored:TLV-84.2, 108MHz.
31/12/1969
16:00:34    3    CMSTATUS:DS_Diplexer_Mode_Change_Ignored:TLV-84.3, 1002MHz.
31/12/1969
16:00:34    3    CMSTATUS:US_Diplexer_Mode_Change:TLV-84.1, 5-42MHz.
31/12/1969
16:00:15    3    CMSTATUS:US_Diplexer_Mode_Change:Init, 5-42MHz.
31/12/1969
16:00:19    3    SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=ac:db:48:bd:36:c9;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
31/12/1969
16:00:21    3    CMSTATUS:DS_Diplexer_Mode_Change_Ignored:TLV-21.2, 258MHz.
31/12/1969
16:00:21    3    CMSTATUS:DS_Diplexer_Mode_Change_Ignored:TLV-21.3, 1002MHz.
31/12/1969
16:00:21    3    CMSTATUS:US_Diplexer_Mode_Change_Ignored:TLV-21.1, 42MHz.
31/12/1969
16:00:25    6    Honoring MDD; IP provisioning mode = IPv6
31/12/1969
16:00:33    3    CMSTATUS:DS_Diplexer_Mode_Change_Ignored:TLV-84.2, 108MHz.
31/12/1969
16:00:33    3    CMSTATUS:DS_Diplexer_Mode_Change_Ignored:TLV-84.3, 1002MHz.
31/12/1969
16:00:33    3    CMSTATUS:US_Diplexer_Mode_Change:TLV-84.1, 5-42MHz.
11/7/2022
05:42:47    6    DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1.;CM-MAC=ac:db:48:bd:36:c9;CMTS-MAC=00:90:f0:27:05:00;CM-QOS=1.1;CM-VER=3.1;
11/7/2022
07:03:44    3    Successful LAN WebGUI login from 76.132.164.13 on 22/07/11 at 7:03 AM.

 

[geobernd]

Yes indeed. Looks like you are losing downstream signal at some point. Once it's gone for more than a few seconds the modem reboots. Interestingly on reboot the signal is still not quite there yet - see the additional SYNC Timing errors.... but comes back before another reboot....
These reboots will happen every few minutes while the signal is gone - so if it is gone for longer you will see multiple down/up messages in the Asus log...
Check all Coax line connectors are hand-tight - the next step would be to open a trouble ticket with Xfinity/Comcast...