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DNS error under load

Last response: in Networking
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February 27, 2013 9:43:25 PM

Hello everyone!

I really need some help today. I have had issues with my home network for more than a year. Today, I decided to scrap everything and do a fresh install hopping that I would get my problem fixed. Guess what...it didn't. So I am here asking for any help! There is good amount of info below, but I tried to organize everything so that it is easier to read/understand. :D 

The gear
Modem (also used as router #1): 2wire 2701HG-G (my ISP's modem)
Gigabit smart switch: Linksys SLM 2024
router #2: D-link Dir-825
router #3: Asus RT-N12


The problem
Under normal load, my network is working fine. However, when under heavier load (torrent, streaming HD movies, etc.), my internet simply stops responding and eventually gives me DNS errors. However, the content being initially loaded with keep on loading at a fast speed. For example, if I am downloading a torrent on a computer, it will slow the whole network down to a point where it's not even working anymore, but the torrent will continue to download at a speed of 450-700 kbps depending on the torrent. Same with movies. If I watch a movie (HD) on my apple tv, the whole movie will play just fine. However, until the movie finishes loading in the apple TV's internal buffer, other devices won't be able to use Internet on the network only 95% of the time.

Network size
Although this is a home network, I think you could compare the size of this network to the one of a small business. The area to cover is rather large (hence the three routers). There are between 15 and 30 devices connected to the network at all times, including three computers (wired), several laptops (wifi), a NetGear ReadyNas NV+ (wired), a gaming server (wired), several smart phones (wifi), apple tv (wired), five Sonos ZonePlayer (for music, wired), xbox 360, etc.

The setup
Here is how I setup the network today. Following the Ultimate modem/router thread. I started by the two slaves routers. I set their IP addresses to 10.128.3.251 and 10.128.3.252 (no it is not the real IPs I used, but the logic is the same). I turned off DHCP server, point their DNS to 10.128.3.250 (which will be my master - the modem) and setup the wifi with a secure connection using the same name and password. Then, I moved along to my modem. I assigned it the IP 10.128.3.250, enable DHCP server, set his range of IPs from 10.128.3.1 to 10.128.3.249, and set it's DNS to OpenDNS's one (to make sure the DNS issue is not caused by my ISP). Configured the wifi with same name and password, again. Then I connected all of my cables. From the modem to the switch, and from the switch to every other devices in the house (the two routers are connected to the LAN connection, not the WAN, as stated in the Ultimate modem/router thread).

The conclusion
After having done all of this, I start a few torrents, wait for a minute or two, try connecting to www.google.com, wait, wait, wait, DNS error (tried it from multiple computers).

Questions
-What could be the possible causes of this problem?
-Could it be that my modem is not able to handle all of the connections? Even though I changed it's dns to OpenDNS' one?
-Does my connection speed affect my network? That is, if I have a [D:6Mbps U:0.70Mbps] connection, would having a [D:15Mbps U:15Mbps] connection help in any way?
-Is it normal for the network to drain all of it's "available internet speed" to one computer, and leave the rest of the network with a connection so slow that it doesn't even work and eventually gives DNS errors?
-Any idea(s) of how to fix this ? :??: 



Thanks a lot!

More about : dns error load

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February 27, 2013 10:06:37 PM
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Several points.

Just for the record, revealing your *private* IP network (10.x.x.x) risks nothing. That’s all happening BEHIND your router. Anyone can use those addresses. It's only your *public* IP you probably want to hide. It only concerns me for one reason; sometimes ppl type what they believe are the correct IPs, and not what’s actually configured.

As far as the basic configuration, I don’t see anything obviously wrong. Because these two additional routers are only wireless APs, their DNS configurations are basically irrelevant. The only DNS that is relevant is on the primary router.

When you have that many devices and traffic, it is possible for a few, perhaps even ONE device to dominate the network. That’s why when it becomes big enough, you might need to consider using QoS controls. It will not only let you prioritize traffic, but w/ a good one, limit traffic on a MAC/IP basis. It will cut back a bit of your top end speed, but in exchange you get more control and less chance of network saturation. Because once the network is heavily congested, any query could fail, even DNS.

You might also be a victim of Bufferbloat ( http://en.wikipedia.org/wiki/Bufferbloat ), a growing problem.

Torrents are also notorious for eating up network resources. Some of the lower end routers simply can’t handle it, or at least not very well. And that 2wire 2701HG-G qualifies a VERY low end! You might want to consider demoting it to only a modem and bridging it to a better router, perhaps one of the other two. Or else upgrade to a new high end router.
February 27, 2013 10:33:05 PM

Thanks a lot for your quick reply!!

eibgrad said:
Several points.
Just for the record, revealing your *private* IP network (10.x.x.x) risks nothing. That’s all happening BEHIND your router. Anyone can use those addresses. It's only your *public* IP you probably want to hide.

Indeed, I forgot about the fact that the IP addresses inside my network are not so "confidential".
eibgrad said:

It only concerns me for one reason; sometimes ppl type what they believe are the correct IPs, and not what’s actually configured.

I'm not sure I understand what you mean there...
eibgrad said:

As far as the basic configuration, I don’t see anything obviously wrong. Because these two additional routers are only wireless APs, their DNS configurations are basically irrelevant. The only DNS that is relevant is on the primary router.

Correct
eibgrad said:

When you have that many devices and traffic, it is possible for a few, perhaps even ONE device to dominate the network. That’s why when it becomes big enough, you might need to consider using QoS controls. It will not only let you prioritize traffic, but w/ a good one, limit traffic on a MAC/IP basis. It will cut back a bit of your top end speed, but in exchange you get more control and less chance of network saturation. Because once the network is heavily congested, any query could fail, even DNS.

I will definitely try to learn more about QoS controls.
eibgrad said:

You might also be a victim of Bufferbloat ( http://en.wikipedia.org/wiki/Bufferbloat ), a growing problem.

Although it might be possible, I think there is a very low probability that this is my problem.
eibgrad said:

Torrents are also notorious for eating up network resources. Some of the lower end routers simply can’t handle it, or at least not very well. And that 2wire 2701HG-G qualifies a VERY low end! You might want to consider demoting it to only a modem and bridging it to a better router, perhaps one of the other two. Or else upgrade to a new high end router.

The 2wire is very bad, yes! I have already planned for my ISP to send me a new, more powerful one. I might even consider turning off the modem's Wifi and adding a dedicated router right beside it. Could that also help?

Edit: I have contacted my ISP, they will provide me with a sagemcom 2864 modem. Is it any better? I will also get [D:50Mbps U:50Mbps] instead of [D:6Mbps U:0.70Mbps] for 20$ less per month (the call was worth it! :)  )

Edit 2: I started to look at QoS and from what I can see, it can control the amount of data that specific MAC/IP are using on the network. However, when I am streaming an HD movie on my computer, then nothing else than that movie will load. That is, on the same computer, I won't be able to browse the Internet or play games, but the movie will continue to load just fine. I don't think QoS is able to solve this kind of problem, can it????

Does simply enabling QoS help or it does nothing until you start to apply rules?

Edit 3: I just realized that my switch already has QoS enabled. It has a LOT of different settings that have been left untouched, but the QoS is set to "Basic" (enabled).
Related resources
March 7, 2013 2:03:21 PM

Best answer selected by elite_thut.
March 7, 2013 2:04:39 PM

Just wanted to say that my problem is fixed. With my new 20/20 connection I was able to setup very effective QoS. I also bridged my ISP modem to a asus rt-n66u router with tomato firmware... All of my network can now use the network no mather what others are doing! Great! Thanks
March 7, 2013 2:27:54 PM

Good to hear, thanx for the feedback, nice to know when something was fixed.
!