Why am I losing 60% of my bandwidth when I connect a router?

March 13, 2016 9:58 AM

I have a fast fiber optic Internet connection, and it works great when wired directly into my PC. But as soon as I connect a router, I lose 60% or more of the download speed.

My fiber optic connection is rated at 500 megabits per second (Mbps) down and 50 Mbps up. When the modem is wired directly into my desktop PC, I do get those speeds. But as soon as I go through a router, I lose most of the download speed (though the upload speed is unaffected).

The first router I tried was a Netgear WNR3500L with Tomato firmware. It's rated for gigabit speeds. However, I was getting a maximum of about 140 Mbps down.

So I tried a more-expensive router. It's an ASUS RT-N66U (again, rated for gigabit speeds). I flashed it with Tomato. This time I did a little better, getting about 200 Mbps down.

For both routers, QoS and bandwidth limiting were disabled in Tomato. And, of course, there were multiple reboots and power-cycles involved in the testing.

I thought the problem might be the network cables, so I tried various different cables, including expensive Cat7 cables with gold-plated connectors. No effect.

I don't know what else to try, and I'm not excited about buying a third router.

posted by alex1965 to Computers & Internet (8 answers total)

I am not an IT professional by any means. But I have noticed that every place I've worked has used switches with high-capacity backplanes, and have connected any WiFi base stations to the switch, and then connected the switch to the router (and the router to the WAN, of course). For situations where high performance is critical, I'd probably use that kind of gear setup rather than any all-in-one boxes.
posted by infinitewindow at 10:29 AM on March 13, 2016

Best answer: Just to confirm, you're talking about the bandwidth between your PC (connected to the router via Ethernet) and the internet, right?

Did you try testing the router's performance with the original firmware? Tomato seems to be an old, abandoned project -- it hasn't been updated in almost 6 years, and I wouldn't count on it giving good performance with modern hardware.

(The "gigabit" label is a simplification for marketing purposes. The router's Ethernet ports can send data at 1 gigabit/second (minus a small amount of per-packet overhead) and it contains a built-in switch that can forward packets from between LAN ports in hardware, at full speed. But when data has to transit between the LAN and the internet, the router's software has to pull packets off an internal queue, examine them, and rewrite them with different IP addresses. So the OS version you run makes a big difference to performance.)
posted by teraflop at 10:37 AM on March 13, 2016

Response by poster: Yes, the speeds refer to the bandwidth between the PC and the Internet, via a wired connection (either directly to the fiber optic modem or through the router).

Unfortunately, I didn't try the original firmware.

The ASUS router is running Tomato Shibby 1.28, which I think is a fairly recent build. Not sure about the Netgear router (it's currently in storage).

I ran some Google searches, trying to find out if Tomato might be responsible for slow speeds, but I couldn't find any discussion of such an issue.
posted by alex1965 at 10:46 AM on March 13, 2016

Gigabit speeds are still pretty rare and hard for consumer routers. But I would expect a RT-N66U to be capable of delivering 500Mbps over wired connections. I'm less confident Tomato will deliver that; it's gotten pretty long in the tooth. I'm not surprised you're having a problem, and would expect to do more research to find a consumer router that can deliver your speed.

One thing to try is to configure the router to be pass-through, not NAT. Disable as much firewalling as you can, too. Newer routers are starting to include hardware acceleration for NAT, basically so the Linux kernel inside the router doesn't have to spend CPU time modifying every packet while doing NAT routing. Third party firmware may or may not have the drivers necessary to support this hardware acceleration. I forget the details on the RT-N66U, whether it has this capability.

I've given up on Tomato, it's just too old and fragmented for me now. The Shibby builds were best last I looked though. I'm using OpenWRT these days which works pretty well but is not as friendly to use. DD-WRT is still a good choice. It's worth your time to try reverting to the stock firmware, too, just to rule out a deeper problem.
posted by Nelson at 10:49 AM on March 13, 2016

Best answer: Those may be rated for gigabit speeds, but I wouldn't really count on either of those to actually give you gigabit routing between the LAN and the WAN. That's a somewhat challenging task and you actually may need to fork out a fair bit to get there. The N66u is an awesome router, but it's about five years old now. And switching your firmware to Tomato isn't helping - the original firmware has drivers that are tweaked for your router.

For instance: my Linksys wrt1900ac does handle a gigabit connection with the stock firmware (~910 down/930 up), but with this week's (more or less officially supported) dd-wrt firmware it drops into the 700s, and the wireless performance is also pretty much ruined.
posted by wotsac at 10:49 AM on March 13, 2016 [1 favorite]

Response by poster: OK, I think that Tomato is the culprit, after all. There's an interesting discussion here, for example.

I'll have to restore the original firmware to the ASUS router. Unfortunately, the Tomato firmware has a feature that's very useful to me -- namely, bandwidth graphs for each device on the network. The ASUS firmware can't do that.
posted by alex1965 at 11:17 AM on March 13, 2016

Best answer: I'm not sure if it has that specific feature you're looking for, but you might also look into Asuswrt-Merlin.
posted by Pryde at 2:53 PM on March 13, 2016 [1 favorite]

Best answer: Its worth looking at the Asus Merlin stuff - that's got some neat stuff and it starts with the Asus firmware and improves it, instead of being a totally new firmware.
posted by wotsac at 4:33 PM on March 13, 2016