Regular internet connection drops with AC66U

[worf0815]

Hello,

I've a rather strange issue with my RT-AC66U and the latest Merlin-Build (3.0.0.4.374.35_4): Every 15 Minutes the connection to the Cable-Modem (Technicolor 6700) and thus the internet drops completely and is automatically re-established after 30 - 60 seconds ("Timer" starts upon initialisation of the cable-modem). In the logs (cable-modem and AC66U) I do not see any suspicious entries.

What is interesting though is, that this behaviour stops and everything is back to normal when I remove any devices connected via cable on lan ports 1-4 and have only wireless devices working (and the cable modem connected).

The general set-up is:
1. Cable-modem in Router-Mode (Bridge disabled by Provider) and AC-66U configured as DMZ-Host.
2. AC-66U Connected via CAT5e Cable to the Modem and WAN configured as static IP.
3. (Unmanaged) Layer-2 Switch connected to AC-66U with various devices connected.

To check for cable issues, I directly connected my laptop with a CAT5e cable to the AC-66U (and removed everything else, except the connection to the cable modem), but the issue still persisted.

Any help and thoughts how to further address this issue would be greatly appreciated.

 

[RMerlin]

Check the router's System Log to see if there's more info as to what is actually happening when it goes down.

 

[worf0815]

Checking /tmp/syslog.log revealed only the information below (dropped packets). The times it disconnected were 10:21, 10:36 and 10:51. IP 192.168.0.1 is the cable modem address (nothing at all in the modem log for the specific time frames).

Pinging 8.8.8.8 from the AC66U showed that roughly 40 - 50 packets were dropped during the connection outage. Pinging the public IP of the cable modem from outside showed no hints of an issue and the ping didn't dropped any packages (tried from my mobile only connected to the UMTS Network).

Jan 10 10:20:39 dropbear[2134]: Password auth succeeded for 'admin' from 192.168.1.192:59060
Jan 10 10:21:31 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:21:31 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:23:37 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:23:37 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:24:41 kernel: DROP <4>DROPIN=eth0 OUT= MAC=28:cf:da:1b:8b:c1:cc:35:40:2e:43:92:08:00 <1>SRC=78.137.47.49 DST=192.168.0.2 <1>LEN=60 TOS=0x00 PREC=0x00 TTL=55 ID=47329 DF PROTO=TCP <1>SPT=49779 DPT=23 SEQ=432032282 ACK=0 WINDOW=5808 RES=0x00 SYN URGP=0 OPT (020405AC0402080A1355F2FB0000000001030301) 
Jan 10 10:25:43 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:25:43 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:27:49 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:27:49 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:29:55 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:29:55 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:32:01 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:32:01 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:34:07 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:34:07 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:34:21 kernel: DROP <4>DROPIN=eth0 OUT= MAC=28:cf:da:1b:8b:c1:cc:35:40:2e:43:92:08:00 <1>SRC=93.174.93.67 DST=192.168.0.2 <1>LEN=40 TOS=0x00 PREC=0x00 TTL=243 ID=54321 PROTO=TCP <1>SPT=58907 DPT=21320 SEQ=181526018 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 
Jan 10 10:36:13 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:36:13 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:38:19 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:38:19 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:40:25 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:40:25 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:42:31 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:42:31 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:44:37 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:44:37 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:46:43 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:46:43 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:48:49 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:48:49 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:50:55 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:50:55 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:51:03 kernel: DROP <4>DROPIN=eth0 OUT= MAC=28:cf:da:1b:8b:c1:cc:35:40:2e:43:92:08:00 <1>SRC=58.215.56.110 DST=192.168.0.2 <1>LEN=48 TOS=0x00 PREC=0x00 TTL=109 ID=9064 PROTO=TCP <1>SPT=30393 DPT=22 SEQ=2138086530 ACK=1486146007 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B401010402) 
Jan 10 10:53:01 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=32 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2 
Jan 10 10:53:01 kernel: DROP <4>DROPIN=eth0 OUT= MAC=01:00:5e:00:00:01:cc:35:40:2e:43:92:08:00 <1>SRC=192.168.0.1 DST=224.0.0.1 <1>LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 OPT (94040000) PROTO=2

 

[RMerlin]

These are just broadcast packets blocked by the firewall that were sent by your modem which seem to also be configured as a router, they don't give any detail regarding the state of the WAN interface. Look for anything talking about WAN interface going down/being restored, or a DHCP lease being dropped/renewed.

 

[worf0815]

Unfortunately this is part of the problem, as there are no additional entries in the AC-66U log (/tmp/syslog) when these connection interruption occur. Any other logs to check or somehow increase verbosity?

Also the cable-modem/router (only works in router mode, as ISP has disabled bridge mode) does not show anything unusual...

 

[mobileman88]

Unfortunately this is part of the problem, as there are no additional entries in the AC-66U log (/tmp/syslog) when these connection interruption occur. Any other logs to check or somehow increase verbosity?

Also the cable-modem/router (only works in router mode, as ISP has disabled bridge mode) does not show anything unusual...

If you suspect it is some network issue, what I did previously to find the problem was to get the Wan port of your Asus and cable modem plugged to a managed switch and get it to spam to a pc running Wire shark. Then look at all the packets generated when a disconnect occurs. This helped me fixed many network issues

 

[worf0815]

Thanks, I will try this one out. Any hints as to what features the managed switch needs to support your suggested analysis, since I've to buy myself a new one?

 

[RMerlin]

Then that tells us that the WAN itself didn't fully drop.

Try a traceroute instead of a ping to see if you can at least make it to your router, or if it always get cut beyond the router. That will help pinpoint if the problem is on the LAN side or on the WAN side/with the ISP.

 

[worf0815]

Did a tracroute as suggested and the issue is on the LAN-Side. During the connectivity issue, traceroute could not reach the cable-modem/router (see below, cable-modem being 192.168.0.1).

admin@RT-AC66U:/tmp/home/root# traceroute -w 1 -n -I 193.99.144.85
traceroute to 193.99.144.85 (193.99.144.85), 30 hops max, 38 byte packets
1 * * *
2 * * *
3 * * *
4 * * *

admin@RT-AC66U:/tmp/home/root# traceroute -w 1 -n -I 193.99.144.85
traceroute to 193.99.144.85 (193.99.144.85), 30 hops max, 38 byte packets
1 * * 192.168.0.1 0.515 ms
2 * * *
3 172.30.21.89 7.547 ms 10.123 ms 10.081 ms
4 172.30.21.253 8.009 ms 35.153 ms 12.389 ms
5 78.42.40.11 18.616 ms 12.295 ms 24.263 ms
6 80.81.193.132 9.669 ms 12.108 ms 10.163 ms
7 82.98.98.102 21.155 ms 12.478 ms 23.383 ms
8 193.99.144.85 14.508 ms 12.294 ms 11.990 ms

 

[RMerlin]

Did a tracroute as suggested and the issue is on the LAN-Side. During the connectivity issue, traceroute could not reach the cable-modem/router (see below, cable-modem being 192.168.0.1).

If your first hop is your modem at 192.168.0.1, then where's your router in there? The router should be the first hop in a traceroute, not the modem.

Make sure you don't have an IP conflict between the router and the modem.

 

[jlake]

Your general setup:

1. Ok
2. Don't configure WAN as static. Use DHCP. Then use dhcp reservations on your gateway.
3. Ok.

 

[worf0815]

Sorry for the confusion, but I did the traceroute test directly from the router. General setup is

• AC-66U on LAN Network configured as router for network 192.168.1.1/255.255.255.0 (network from which the connection drops occur).
• AC-66U on WAN-Network configured with 192.168.0.2/255.255.255.252.
• Cable-Modem/Router configured with 192.168.0.1/255.255.255.252.
• Unfortunately the ISP has disabled Bridge-Mode on the Cable-Modem, so I've put the IP of my AC-66U in the "DMZ" entry of the Cable-Modem/Router.

Traceroute still show that it is somehow broken between the cable-modem and AC-66U Connection:

192.168.1.21>> tracert -d -w 1 8.8.8.8
 1    <1 ms    <1 ms    <1 ms  192.168.1.1
 2    <1 ms    <1 ms    <1 ms  192.168.0.1
 3     *        *        *     Zeitüberschreitung der Anforderung.
 4     7 ms    15 ms     7 ms  172.30.21.89
 5    14 ms    23 ms     6 ms  172.30.21.253
 6    10 ms    10 ms    11 ms  78.42.40.11
 7     9 ms    72 ms    12 ms  72.14.212.70
 8    12 ms    10 ms    11 ms  72.14.238.44
 9    11 ms    13 ms    29 ms  209.85.251.248
10    12 ms    13 ms    10 ms  209.85.254.116
11     *        *        *     Zeitüberschreitung der Anforderung.
12    12 ms    11 ms    14 ms  8.8.8.8

192.168.1.21>> tracert -d -w 1 8.8.8.8
 1    <1 ms    <1 ms    <1 ms  192.168.1.1
 2     *        *        *     Zeitüberschreitung der Anforderung.
 3     *        *        *     Zeitüberschreitung der Anforderung.
 4     *        *        *     Zeitüberschreitung der Anforderung.
 5     *        *        *     Zeitüberschreitung der Anforderung.
 6     *        *        *     Zeitüberschreitung der Anforderung.
 7     *        *        *     Zeitüberschreitung der Anforderung.
 8     *        *        *     Zeitüberschreitung der Anforderung.
 9     *        *        *     Zeitüberschreitung der Anforderung.
10     *        *        *     Zeitüberschreitung der Anforderung.

 

[RMerlin]

If you get packet losses between the router WAN and the modem LAN then my first guess would be a problem with the Ethernet cable between them, or a hardware issue with either the modem or the router Ethernet port.

Make sure everyone is on the same MTU (modem and router), just to be safe.

 

[worf0815]

Cable was also my first guess, so I did change the cable and bought a new CAT6-Cable but still no luck.

Strangely enough so, the connection drops do not occur, if I remove all cables from the LAN-Port and have only wireless devices connected to the AC66U.

Another strange thing is, that I connected today from my workplace via OpenVPN to my home-network. During the connection issue I had an SSH-Session to the AC-66U running which continued to stay in place, even if the ping/traceroute got stuck like seen in the previous posts?

 

[gendrol75]

Cable was also my first guess, so I did change the cable and bought a new CAT6-Cable but still no luck.

Strangely enough so, the connection drops do not occur, if I remove all cables from the LAN-Port and have only wireless devices connected to the AC66U.

Another strange thing is, that I connected today from my workplace via OpenVPN to my home-network. During the connection issue I had an SSH-Session to the AC-66U running which continued to stay in place, even if the ping/traceroute got stuck like seen in the previous posts?

I've had exactly this problem with my brand new RT-AC66U. Every 15 minutes (exactly) my pings would start to drop packets for 15-30 seconds. During this interval the WAN would appear to all machines to be down. However, VOIP conversations as well as IM sessions over VPN would continue to work. No signs of anything wrong in the router or cable modem logs.

At first I assumed the problem was my ISP, but when I connected a machine directly to the cable modem, everything seemed to work fine. I didn't experiment with unplugging all wired devices from the router as you did.

For me, the problem appears to have been solved by replacing the AC66U stock firmware with Merlin 3.0.0.4.374.40_0. (I doubt it made any difference, but I also made sure to use the same cable modem port that worked in the direct connection test). I didn't see anything obviously relevant in the Merlin changelogs since the v35_4 that you're running, but there have been a LOT of fixes and I'm just happy enough to have it stable again.

Over 24 hours now, and no sign of dropped packets ...

 

[gendrol75]

BTW, my cable modem is also a Technicolor ... TC.7200U, and my setup looks identical to yours (with the exception of the unmanaged switch).

 

[worf0815]

I also figured out (with the managed switch) that somehow the TC.7200U was not only replying for DNS-Queries for 192.168.0.x/255.255.255.0 (hard coded in the device) but somehow also for 192.168.1.x/255.255.255.0 (bug in the TC.7200U???). This resulted in duplicate ARP-Requests/Responses from both the TC.7200U and the AC66U, which was configured with 192.168.1.x for the internal network.

After changing the AC66U LAN-Network configuration to something else (e.g. 192.168.16.x ) everything worked as it should...