I have tested latest ASUS firmware for RT-AC68U (Version 18.104.22.168.384.81049
published at 2019/09/05)
as stated here: https://www.asus.com/support/FAQ/1037368/
Temporary disconnections while executing failover or failback is normal. If you find your network frequently disconnects from the Internet, please navigate to the ASUS Support Site
to report the problem you've encountered or contact ASUS Product Support
for additional assistance.
this is complete non-sense, why should working Secondary WAN connection during fail-back scenario be disconnected every X seconds, just because of broken DUAL WAN logic
ASUS is not testing Internet at all before doing fail-back, it is just observing LINK STATUS (UP or DOWN) but your Primary WAN is "UP" because xDSL or COAX modem is connected, even when your ISP has outage, and you can't ping any of the following Public DNS servers:
22.214.171.124 - OpenDNS Public DNS
126.96.36.199 - Google Public DNS
188.8.131.52 - CloudFlare Public DNS
I did the following test using own Virtual Private Server with static public IP address
I have defined in ASUS Dual WAN - Network Monitoring - PING - and wrote IP address from my VPS in that field
SSH to my VPS, and run this command in order to block PING (ICMP) so I can simulate network destination is not reachable
sudo iptables -I INPUT -s xxx.yyy.zzz.qqq -p icmp --icmp-type echo-request -j REJECT
replace xxx.yyy.zzz.qqq with your Primary WAN IP
you can find out your Primary WAN IP using one of the following links:
after fail-over period (5 sec x 3 times = 15 sec) in my case, router has switched to Secondary WAN - very good
however, internet connection was breaking every X seconds period, defined in your fail-back scenario - very bad
in order to avoid breaking working Internet connection, ASUS router should ping Primary WAN connection, while using Secodary WAN
here is how ASUS can test primary and secondary WAN without interuption active connection
ping -I ppp0 184.108.40.206 -c 3 && ping -I ppp0 220.127.116.11 -c 3 && ping -I ppp0 18.104.22.168 -c 3
ping -I vlan2 22.214.171.124 -c 3 && ping -I vlan2 126.96.36.199 -c 3 && ping -I vlan2 188.8.131.52 -c 3
you can replace interface name with Primary WAN and Secondary WAN interface names
after Primary WAN is working for let's say 2 minutes (120 seconds), ASUS router should fail-back from Secondary WAN back to Primary WAN
I would love to see more than one target, in order to prevent false positives!!!
DNS Query testing was not reliable method, due to DNS cache in router!
ASUS didn't switched connections, even there was no Internet on Primary WAN
best way to test connection is PING (ICMP) followed by CURL (HTTP/S)
curl --interface ppp0 --connect-timeout 5 -s "http://ipecho.net/plain"
curl --interface ppp0 --connect-timeout 5 -s "http://whatismyip.akamai.com"
curl --interface ppp0 --connect-timeout 5 -s "https://ifconfig.co/"
curl --interface vlan2 --connect-timeout 5 -s "http://ipecho.net/plain"
curl --interface vlan2 --connect-timeout 5 -s "http://whatismyip.akamai.com"
curl --interface vlan2 --connect-timeout 5 -s "https://ifconfig.co/"
Asus firmware doesn't contain CURL command, but Merlin Firwmare contains CURL command, and ASUS should adopt this
this is guideline how ASUS should fix broken DUAL WAN logic
please help us gather more crowd to report these issues and get ASUS to resolve this, so we can enjoy features we have paid for when we bought our routers
guide how to report issue with ASUS Support: https://www.snbforums.com/threads/beta-dual-wan-helper-script-discontinued.40401/page-8#post-412417