ASUS RT-N66U with LAN-WAN performance problem

[DK-9000]

I just received and connected my new RT-N66U, but when testing throughput I encountered a performance problem.
The Router is connected to a 100Mbit Internet connection, but my upload isn’t going past 70Mbit/s when testing.

The Router is running firmware version 3.0.0.3.108.

As reference: when my laptop is connected directly to the ISP (LAN speed 100M) I measure 94,43 Mbit/s download and 92,97 Mbit/s upload.

But performance degrades when the N66U is connected between my ISP and the laptop.
ISP <100Mbit> N66U <1Gbit> Laptop = 94,40 Mbit/s download and 69,00 Mbit/s upload.

If I force the laptop LAN port to 100Mbit the performance is back at the expected speed.
ISP <100Mbit> N66U<100Mbit> Laptop = 94,40 Mbit/s download and 92,40 Mbit/s upload.

I assume the reason is because the computer is uploading on the Gigabit port faster than the router can send data on the 100Mbit WAN port.
But is this due to a problem in the N66U, like too small packet buffer resulting in high levels of packet delay and loss or is it elsewhere?
When a network is in such a condition, it has settled (under overload) into a stable state where traffic demand is high but less useful throughput is available.

I expect to have the fast Internet connection (limited only by 100M ISP port speed), but at the same time I want the benefits of having a Gb LAN network.

Is this a problem that’s solvable?

 

[TonyH]

If possible just set the laptop WiFi card link speed to auto mode and you have to configure QOS to your liking.. That is what I'd do.

 

[DK-9000]

I’m using wired connection because I want to reach Gig-speed between connected equipment on the LAN side.
The computer NIC is in auto mode and of course it links at 1000Mbit full duplex.

Upload is way less than expected when link speed is higher on LAN side then on WAN side.
Only when I fix the LAN at 100M (same as WAN auto negotiates with ISP equipment) can I get full throughput between LAN and WAN.
But this is not an option, because I need Gig on the LAN side.

You might be on to something in regards to QoS – but what do I have to configure?

 

[frimp]

Hi,

I put a Gigabit-switch before the router, where all local devices are connected (Cisco Linksys SLM2008 with 8 Gbit/s throughput). This will offload LAN-switching from the router.

Also check if flow control (802.3x) has been enabled on the router (if possible) and the PC and switch.

 

[thiggins]

Try running a long series of pings and look for packet loss. Could be an incompatibility between the router's switch and your laptop Ethernet NIC.

Try putting a Gigabit switch between your laptop and the router.

 

[jgm]

Mtu?

One thing that might be worth checking is the MTU of the router. I'm running .108 and it appears that enabling jumbo frames does not have any effect.

Specifically, even after enabling jumbo frames (in LAN/Switch Control) it appears that the MTU remains low:

admin@RT-N66U:/tmp/etc# ip route get 10.0.0.2
10.0.0.2 dev br0 src 10.0.0.1
cache mtu 1500 advmss 1460 metric 10 64

(In this instance 10.0.0.1 is the LAN IP of the router).

If this is the same on your router then chances are that this is limiting the overall throughput. I haven't attempted to force this manually to see if it makes a difference as my internet connection is nowhere near fast enough for it to matter.

Note that if you do attempt this you will need to set MTU on your eth* interfaces as well as your br0 interface

 

[Deepcuts]

It is from QoS
Disabled, your upload is lower then when QoS is enabled.
Weird I know, but this is reality. Asus's reality.
Try it.

 

[kompis]

Did you ever find a solution for this? I'm experiencing the same issue..

 

[Zirescu]

Have you tried updating the firmware to the latest?