LAN sluggish to nothing only with router

[smd12]

I've been battling a problem for over 2 weeks now so I'm looking for any possible help. Everything was fine up until 2 1/2 weeks ago. Since then, I can sometimes connect to websites and sometime not. This only happens when I go through the router. If I go direct from the modem, everything is good again. I see this on my desktop, my laptop, and work laptop so I doubt it's a computer issue. All cables are CAT 5e. A little history:
1. Started with an Arris 6141 modem and Asus RT-N66U router.
2. Updated the firmware for the router - no change.
3. Loaded Merlin firmware - no change
4. Several attemps with hard resets and power downs - no change
5. Replaced the modem with Arris 6190 and loaded the newest firmware - no change
6. More resets - no change
7. Changed speed & Duplex to 1 Gbps Full Duplex - no change
8. Replace router with Asus RT-AC87U - no change
9. More resets - no change

Tonight Speedtest shows the same with or without the router - 120.12/6.01
Tonight with the router I was able to get into Google in a second or two. I waited 4min for Amazon to load and it never did. Yahoo timed out after about 30s.
Going directly from the modem to my desktop, all 3 sites loaded right away.

Also, regardless of which router, if I log into the router and go and ping websites, I can always get to Google on 5 pings in about 30ms. Yahoo sometimes has some loss. I've yet to be able to get any pings to Amazon. It's always 100% loss. I see that even if I've just been on the Amazon site as it does load sometimes.

I'm at a loss were to go from here. Any help is greatly appreciated!

Thanks,
smd12

 

[System Error Message]

This sounds like an issue with SSL and MTU or just the MTU in general. You need to lower your MTU on WAN. Your LAN isnt sluggish, its your WAN that is sluggish. did you ping your own router first? What you need to do is lower the MTU on WAN first. If the problem still persist than try lowering the TCP MSS.

You should also contact your ISP, perhaps the line is faulty?

 

[Nullity]

Share your network topology.

 

[L&LD]

http://www.snbforums.com/threads/rt-ac66u-slow-wan-to-lan.12973/page-3#post-269410

 

[sfx2000]

Try a different browser, try another computer, see if the problem continues..

 

[smd12]

The MTU value comes out to 1472. I don't see anywhere in the Asus interface that I can set it. Where do I do that? From what I've read, I should set it to 1500, correct? I'm also not sure how I would set the TCP MSS.

As far as topology, I've simplified it down to signal into the modem, modem connection to the router wan, router connected to the pc. Every other client is off at this point.

I have tried I.E., Firefox, and Chrome. I've also tried three different pc's.

Thanks,
Smd12

 

[System Error Message]

Sometimes an MTU value too small or too large can cause problems. The standard ethernet is 1500 but when it is not ethernet the MTU is different even for wifi. Try increasing or decreasing MTU until you get to one that works.
If you still cant find one that works than changing the tcp mss if it is bigger than MTU will help, alternatively you can set your LAN MTU to your WAN MTU.

 

[Nullity]

Unless you are using PPPoE, your MTU should be 1500 (which corresponds to 1472 when testing MTU with pings because of the 28 bytes of IP & ICMP overhead, IIRC).


Rather than guessing about why you are having poor performance, I would run a packet sniffer like tcpdump on your router then look at the packet capture with a GUI program like Wireshark. Any network problems will be obvious by appearing in red color when viewing with Wireshark.
Before trying tcpdump on the gateway router you could just try running Wireshark itself at any PC on your LAN and see if anything pops up in red.

You really do not want to try any tweaking or reconfiguring before you actually know what the problem is, as you will likely make things worse.



Make sure that your physical network's topology is setup properly, avoiding any endless loops or other common problems.

 

[RobNY]

The quick and easy check would be set a static IP and DNS. It sounds like a DNS server problem of some kind. I would try 4.2.2.2 for a DNS server assuming your in the US. Have your tried pinging google.com and what are your ping results? I prefer to start troubleshooting with the quick and easy things first before I'd start changing major setting on my network.

-Rob

 

[smd12]

Hi Everyone,
Thank you for the help. I wish I was able to say that I narrowed it down to a specific problem but I didn't. As of Monday 9/26 it wasn't working correctly. When I next logged on, on 9/28, it worked again. It's been ok ever since. I even switched back to my old router and it works too. I hope it doesn't come back again!
smd

 

[Samir]

Sounds like a temporary dns issue that got resolved. Glad everything is back to normal. If it does it again, I'd manually set the google dns entries in the pc that's having problems and then see if that fixes it. Might give us a clue as to what the issue is.

 

[yorgi]

I've been battling a problem for over 2 weeks now so I'm looking for any possible help. Everything was fine up until 2 1/2 weeks ago. Since then, I can sometimes connect to websites and sometime not. This only happens when I go through the router. If I go direct from the modem, everything is good again. I see this on my desktop, my laptop, and work laptop so I doubt it's a computer issue. All cables are CAT 5e. A little history:
1. Started with an Arris 6141 modem and Asus RT-N66U router.
2. Updated the firmware for the router - no change.
3. Loaded Merlin firmware - no change
4. Several attemps with hard resets and power downs - no change
5. Replaced the modem with Arris 6190 and loaded the newest firmware - no change
6. More resets - no change
7. Changed speed & Duplex to 1 Gbps Full Duplex - no change
8. Replace router with Asus RT-AC87U - no change
9. More resets - no change

Tonight Speedtest shows the same with or without the router - 120.12/6.01
Tonight with the router I was able to get into Google in a second or two. I waited 4min for Amazon to load and it never did. Yahoo timed out after about 30s.
Going directly from the modem to my desktop, all 3 sites loaded right away.

Also, regardless of which router, if I log into the router and go and ping websites, I can always get to Google on 5 pings in about 30ms. Yahoo sometimes has some loss. I've yet to be able to get any pings to Amazon. It's always 100% loss. I see that even if I've just been on the Amazon site as it does load sometimes.

I'm at a loss were to go from here. Any help is greatly appreciated!

Thanks,
smd12

I think its your IP pool
go to LAN/DHCP/IP Pool Starting Address 192.168.1.100 and IP Pool ending Address 192.168.1.254
By default ASUS routers take the entire IP pool for DHCP which I find very strange.
If you use DHCP and Static IP addresses and your pool is setup to 192.168.1-192.168.254
there can be major conflicts that happen and one of them is exactly what you are explaining.
I don't think your prolbem is resolved its only a matter of time before it starts again.
Also make sure if you are using 2 routers that you enable DHCP only on one of the Routers.
that is usually another problem that occurs if you have 2 DHCP servers in play.