Occasional no response from DNS server when Dual WAN is on

[02m]

Hi,

I am in the middle of switching my ISP and figured that this is a perfect time to try out the Dual WAN feature. Everything is running smoothly, but I have noticed that occasionally after typing in a website address I instantly get an error in the browser. But after refresh everything is fine again.

I have tried to reproduce it by constantly sending DNS queries to the router by:

watch -e -n 1 "drill test.2m.lt @192.168.1.1 | grep -m 1 SOA"

and I see that is takes less than a minute for watch command to stop, which means that no response has been received from the router DNS server.

When I turn Dual WAN feature off, I was able to leave the above command running at least for 5 minutes without any problems.

I am currently running 378.56_2 F/W version on RT-N66U. Dual WAN mode is "Fallback". I was not able to reproduce it with Dual WAN mode "Balance".

 

[Steve Horbachuk]

I posted something similar.... http://www.snbforums.com/threads/dns-in-dual-wan.29374/

I think it is a bug, it seems DNS queries are going to the standby WAN DNS servers. Is one WAN connection Comcast?

 

[02m]

Wow. Sorry I missed your topic. I tried searching but nothing came up. Probably my crooked fingers.

No, both ISPs are from Lithuania which provide WAN IP address and DNS server configuration via DHCP.

 

[Steve Horbachuk]

Wow. Sorry I missed your topic. I tried searching but nothing came up. Probably my crooked fingers.

No, both ISPs are from Lithuania which provide WAN IP address and DNS server configuration via DHCP.

Actually I think you posted first so my bad on not seeing it

What I am doing for a workaround is unchecking "Connect to DNS Server automatically" and specifying Google's DNS 8.8.8.8 and 8.8.4.4 for both WAN connections. This is a workaround to the problem. I gotta think it's a pretty easy fix to not include the standby WAN's DNS servers in the dnsmasq config however.

 

[Steve Horbachuk]

I also did find this on line 2170 of /release/src/router/rc/wan.c (update_resolvconf)

/* TODO: Skip unused wans
if (wan disabled or inactive and it's not ppp with active man)
continue */

Which means ASUS hasn't gotten around to it yet ?

 

[02m]

Unfortunately I can not use the workaround you mentioned, because then I loose the functionality where local hostnames are resolved to IPs in the LAN.

 

[Steve Horbachuk]

Unfortunately I can not use the workaround you mentioned, because then I loose the functionality where local hostnames are resolved to IPs in the LAN.

No you will not loose that functionality. What I mentioned just changes the DNS servers DNSMasq fowards queries to, will have no affect on LAN

 

[02m]

I see now. You are right.

 

[kvic]

Dual WAN is fun. Think of it as a multiple connection problem, and you get the chance to manage uplink/downlink together with two WANs. A total of 4 combinations. All under your control...configurable using iptables and iproute2 in a linux router.

In ASUSWRT, maybe all other consumer routers too, not only DNS won't respond occasionally, in general you'll get disrupted browsing experience on a constant basis if you opt for load balance mode. Most applications will be upset and not run too.

The other fail-over mode is a waste of bandwidth (being not used for most of the time). Since it's just like a single WAN, more compatible with most applications. So it's a suggested use of dual WAN by vendors. Quite frankly...both are not useful as-is.