WNDR3700v4 in AP mode speed degradation over WAN port

[GGill]

WNDR3700v4 firmware V1.0.2.78

I have the Netgear router set to AP mode, with static IP address, and default gateway set to my Zhone router which faces the outside world. (The Zhone is an ISP-supplied router over which I have little configuration control.)

• On the LAN side of the Netgear I have a desktop with gigabit ethernet card, connected by cable to the Netgear.
• The WAN side of the Netgear is connected to a LAN port on the Zhone router.
• I have a gigabit-ethernet laptop connected to another LAN port on the Zhone router.

To measure speed of the connection between the desktop and laptop, I ran iperf -s (server mode) on the laptop and iperf -c (client mode) on the desktop. The TCP speed was reported as around 3Mbits/s - very slow. With iperf -c -R on the desktop (which reverses the test direction, laptop server is sender instead of desktop client), the TCP speed was about 200Mbits/s.

I then rebooted the Netgear. The iperf reported TCP speed (with -R and without) increased to about 650Mbits/s.

If instead of connecting the WAN port on the Netgear to the Zhone, I connect a LAN port on the Netgear to the Zhone (using the same cable), the desktop and laptop communicate at around 950Mbits/s, close to the maximum theoretical speed of 1Gbit/s. (The Netgear is still in AP mode, though I guess that shouldn't make a difference if not using the Netgear's WAN port.) Similarly, if I skip the Netgear entirely, connecting the desktop directly to a LAN port on the Zhone, I get around 950Mbits/s speed to the laptop.

When in AP mode many config options in the Netgear are inaccessible, so it's hard for me to tell if there's a setting interfering with communication over the WAN port. Also the asymmetrical speeds before the router reboot (3Mbits/s from desktop to laptop, 200Mbits/s from laptop to desktop), and the fact that the reboot fixed that, but still didn't achieve full speed (650Mbits/s), make me suspicious about what is happening on the WAN port side.

The workaround clearly is to ignore the WAN port on the Netgear and use a LAN port to connect to the Zhone, but

• I put the Netgear where it is specifically because I have 4 devices I want to connect to LAN ports, and Netgear's AP mode let me use the WAN port to connect to the rest of the network; and
• I'm still curious to know why there would be a performance problem across the WAN port, if there might be a configuration reason and not just failing hardware. (The Netgear router has been my workhorse for a few years until moving to a new place.)

[ElaineM · Accepted solution]

AP Mode disables hardware acceleration, so the CPU needs to handle packets going between the LAN and WAN ports. The Broadcom chip can handle switching between LAN ports without CPU involvement.

[GGill]

I did search before posting but didn't find this topic until it was suggested after posting:

• WAN OR LAN Port for Access Point

It suggests that WAN port use in AP mode is significantly worse because of extra packet processing. I wonder why that's true - what keeps the WAN port from just being another switched LAN port like the others, when in AP mode?

[ElaineM · Accepted solution]

AP Mode disables hardware acceleration, so the CPU needs to handle packets going between the LAN and WAN ports. The Broadcom chip can handle switching between LAN ports without CPU involvement.