Issues with DNS and 5GHz wireless

[herbnix]

I am currently running the 378.55 build on a RC-AC87U and a RC-AC68U and I have noticed a problem with DNS resolution under both builds - in particular on the wireless side. I am doing nothing spectacular with either - both have had factory resets performed on them, both were running in Routing mode (though I have also noticed the same thing happen in Access Point mode).

Essentially what is happening is this;
- After ~2 days of operation under normal traffic conditions (say 2 people using the routers) I start not being able to perform any DNS resolution under wireless, in particular with the 5GHz band.
- If I have used torrents, which are high on UDP usage, the symptoms become prevalent with the wireless sooner than 2 days.
- I have tried using different DNS servers (local, Google, OpenDNS) but all cannot be reached at all.
- It is only the wireless that seems to be affected. Resolution on the wired side seems to be working fine.

A soft reboot or a flush of the DNS on the router (or the clients) will not resolve the issue. The only way I can resolve the problem is by hard powercycling the routers.

I am using several different clients (Android phones/tablets, Chromcast, TV, Windows/Linux/Apple boxes/Chromebook). The symptoms are quickest to show up on an Apple Air where you have to use Wifi since there is no fixed network lead (though I am sure that I can plug in a USB network adapter). All can connect to the wireless and authenticate successfully (under WPA2) but resolution of DNS (just about the first thing that happens after this) doesn't work at all.

On the WAN side I have a very fast 1gig ethernet pipe. So, there is definitely no issue on that side of things. I have also tried the same two routers on a 100meg feed with the same result.

I was wondering as to whether there is a UDP filter than could be adjusted (I have seen this being done on other routers in the past). Though I can't find a setting for this at all. There are TCP settings but nothing for UDP.

The MTU is set to 1500 and no packets are getting fragmented.

If anyone can offer any suggestions as to what could be the cause then I would really love to know. I have been trying all kinds of things - using the router as a DNS server (though the standard dnsmasq), using public DNS servers, etc.

Appreciate any feedback. The only thing I can trace things down to is something on the router itself since the clients work fine in other environments (and for the period of time before the router hits some sort of wall and needs a reboot) and I have used alternative routers without any issues (embarrassingly enough the ISP-provided router, which is known to be crap, performs better than the Asus!).

 

[herbnix]

I should add a couple of things:
- I have seen this issue before on previous releases of firmware though it happens on 55 more quickly it seems.
- It is happening on BOTH routers. If I had it happen on one then I could write it off as a hardware issue but having it happen on both seems to be a little more than coincidence.

All of this is greatly annoying since I was planning on using remote access through OpenVPN to get onto the system when I am out-and-about (which does indeed work fine). Since the setup isn't reliable - in that if local traffic (say through a torrent kicked off remotely) takes the router down, then I can't bounce traffic through it and a remote reboot won't fix things up either.

I suppose one could write a reboot script with a timer but that is the sort of thing that is dreadfully inelegant and an indirect demonstration that the device you have has issues and should be replaced. I would really like to avoid doing that sort of thing.

Would really like to know whether anyone else has encountered this sort of thing before.

 

[Zirescu]

While I can't say my issue is caused by the same problem, as the issue I see is only afflicting one of my systems. There is something fishy with the .55 firmware and DHCP/DNS. My Lenovo W520 laptop, connected to my N66U drops offline just about once every 24 hrs. DNS resolutions fails and doesn't recover. No DHCP messages show up on the AC87U but yet the laptop can still ping the N66U but not the AC87U. I've got a Dell laptop, also wired to the N66U, which stays connected. Disabling the the LAN and enabling again, doesn't resolve the issue. Disabling the network adapter and enabling it again, doesn't resolve the issue. Flushing the DNS cache, no effect. Oddly, this time I pulled the cable on it and reconnected it and this time it was able to reconnect. I've swapped cables before and tested it multiple times, also tried different ports on the N66u with no effect. It seems like it's some bizarre timing issue as if I just leave it long enough things do end up righting themselves. Originally I thought the problem was related to the Computer Browser service, but that only fixed issues on the Dell. Would love to figure this out too.

 

[LukeH]

This is also happening to me on RT-AC56U with .55 and more often then before (with a twist, see below). Just posting a couple of observations that may help:

I had to disable Smart QoS cause with that the network became quickly unusable after trying to use resources (video) from USB disk attached to router. After that:

For some reason it seems it happens at certain hours: around 1-2AM East EU time, regardless I just started using the notwork or been online for hours (playing video from router's attached disk or playing MMO for example but not necessarily) or restart router when it happens. Web browsers usually show errors regarding DNS timeouts but LAN resources including router's web page (accessed by IP) are unusable too.

Restarting router or just switching back and forth between my normal and guest wifi seems to make it work for about 2 minutes then the issue reoccurs if on that timeframe. Without restart or anything on the router, the next day it seems fine till about the same hour.

Maybe the router's way to tell me I should go to sleep ....

 

[ILMostro]

Is this issue maybe related to another thread here? Namely, http://www.snbforums.com/threads/lo...ue-with-dns-filter-enabled.26298/#post-196575