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Home Networking Question (Fast Ethernet Devices on Gigabit Ethernet Network)


dabretty
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Hi all -

First, great home networking articles (usacomp2k3!).

I have two questions though, with regards to network speeds. You might recall that I thought I had a faulty EX485 from the Newegg deal a few weeks ago, and HP told me to send it back ... due to low network speeds (I was seeing ~250 kbps on a GigE wired connection).

Well, in getting a newer EX495 this past weekend I've flushed out what my problem was. It wasn't the poor EX485's fault! I have a Trendnet TEW-639GR Gigabit-wired (and draft-N wireless) router. They are all gigabit ethernet ports on this thing. Well, essentially what I found this past weekend was that if I forced my PC into 100 Mbps (full duplex) I could see nice transfer speeds (about 90% of theoretical). This led me to think that I had a bad pair in my wiring somewhere.

Tonight I brought home a cable tester from work and verified there was no bad wiring. So I just started doing random things ... and what I found was that just by having another family-room/TV router (10/100 only!) wired into my main gigabit router, it was decreasing the speeds of the entire network. And not just decreasing them to 100Mbps, I mean absolutely killing the PC->gigabit router->WHS connection when all of those devices were trying to talk gigabit (I found myself in the 230 kbps range again).

Is this due to the fact that I have a cheap gigabit router that I'm seeing this behavior? I guess I was mistaken as to thinking that the PC and WHS were talking through a gigabit router, therefore all was well. But the router certainly freaks out with any slower communication going on at the exact same time. If I were to buy a better router would I expect this behavior to be any different?

Also, mostly unrelated ... with only my gigabit devices (PC, WHS) talking on the network, I see speeds of about 160-200 Mbps. From some of my experiences at work I guess I'm not surprised ... but is this due to disk access issues in the devices themselves? I've always been curious as to why I don't think I've experienced the typical 90%-of-theoretical on gigabit wiring, since the disks themselves should be much faster (1.5 Gbps for SATA). But then again I suppose the actual write process is much slower (you can fill the disk's write buffer at 1.5 Gpbs coming in, but you'll actually write to the disk at much slower speeds).

Again, thanks for the great knowledge on this site and in the podcasts ...

Brett

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Hey Brett,
Hypothetically, the presence of a fast ethernet device connected to a gigabit switch should have no bearing whatsoever on your ability to transfer files from/to 2 gigabit devices on that gigabit switch. The router will only pass the data between the 2 devices; it shouldn't ever traverse the the rest of the network.
Now, you said you have a router in the living room? It is functioning as a router, or as a dumb switch.
Lastly, you said that the file transfers happened at ~100mbps when forced to 100mbps-full-duplex mode. Maybe there is something wrong with your NIC. Have you tried looking for updated drivers?
You don't have jumbo frames turned on, do you?

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Thanks for the response. To answer your questions:

- The other router in the other room (seemingly acting as a child to the main one) is a WRT54G operating in Access Point mode (to create another "hotspot" in the house). I need to do some exploration of that though, because now that I think about it the parent network is plugged into it via a standard port (not the WAN port). I had to do this to make it work, for some reason. I'm wondering if I can get it to function with the rest of the network through its WAN port if it may "leave alone" the rest of my network. While it may seem that there are two chiefs in this network, it (the "other" router) is using the main one as its gateway. Ugh ... wish I had time to make a network diagram right now!

- To try to troubleshoot this problem I actually did enable jumbo frames on both my PC and on the WHS, to the largest size supported by both (my PC is limited to 7k). It seemed to have a slight increase in performance, both in 100M mode and 1000M mode (when the slow guy was detached from the network).

I agree this slow router shouldn't have anything to do with it, but now I suspect it has something to do with being connected to the greater network via a standard port (not WAN/uplink). Maybe if it thinks it's effectively in charge it's just freaking out at the sight of these super fast transmissions that make no sense to it. Gigabit stuff is a bit new to me, but I very much remember the days of 10/100 switching and I don't ever recall having issues of the whole network slowing because a 10M device was plugged into it. But, I suppose, that's because it was a pure switch?

Thanks for the suggestions and I'll have to play around with it more tonight when I get home. The WRT54G is operating DD-WRT so I should have a lot of flexibility in terms of getting it into a different/better operating mode.

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Well I'd be willing to bet your problem is with jumbo frames. Try disabling that on both and see if things start working again.

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Okay, I finally got to do some more troubleshooting on this stuff.

I tried disabling jumbo frames on both the WHS and my PC, with no change. I also tried plugging in my Xbox directly to the main router (the "living room" switch is no longer connected), so that there are only three devices on the entire network - (1) WHS/EX495 (1000M), (2) Win7 PC (1000M), and (3) Xbox 360 (100M). The exact same problem still existed, essentially ruling out the possibility that I was having a "network struggle" between the two routers.

Peculiarly, I started looking around online and dug pretty deep ... I found two Newegg reviews for this router (TEW-639GR) that stated the gigabit ports "act like a hub, not a switch." I then contacted TrendNet, who informed me that their latest firmware "fixed unnecessary packet broadcasting." I already loaded the new firmware on there a while ago, so that didn't help either. When I told TrendNet this, they said they would have to make sure they uploaded the right firmware to their website. The same day, their website reflected the same firmware number but a new "upload date" ... however, the firmware appears to be the same as before and doesn't help me. I have not heard anything back from them since.

So, in summary ... it sounds like TrendNet's routers with gigabit ports have issues with acting like a true switch. The fact that I can't get my devices to even operate at 100M (the Xbox speed) when the Xbox is in the loop - but rather kicks it all the way back to a crawling speed - makes me believe this packet broadcasting to all wired ports is the issue. I'm not a TCP/IP protocol expert, but I know there are acknowledgement packets sent by receiving parties to the transmitting parties on a network, for every single packet (hence why TCP/IP is essentially a lossless protocol). My guess is that the 10/100 devices are receiving pieces of 1000 packets and getting thoroughly confused, sending some sort of negative acknowledgement packet back to the sender. This would explain why the 1000M devices drop to super slow speeds, they're getting bombarded with messages from the 10/100 devices that can't understand. It basically ends in a DoS attack on the transmitting devices that are trying to communicate at 1000M.

Stay away from TrendNet routers, at least the TEW-639GR!

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Very interesting. That is a pretty crappy design and an egregious problem. I will keep that in mind.

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This won't help you with the problem exactly, but you might want to look at buying a switch. I have seen on numerous forums that most routers don't do the best job of switching data through their hardwired ethernet ports. If you use a switch, the switch will remember which device is on each port and communication can happen directly from one device to another if they are on the same switch (the router doesn't do any of the work at all).

Do you know if your Trendnet router ever worked properly (as expected)? Sometimes a lighting strike can create a surge that might cause damage but everything seems OK.

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I'm actually about to head out and buy a switch now. I guess I thought I'd get lucky with the TrendNet one, I mean ... it has wireless N as well as four gigabit ports. Seemed like killing two birds with one stone. But the price of it (I got it after rebate for about $65!) should have told me it could be too good to be true.

As far as I know, the TrendNet router never worked properly in terms of gigabit switching. I've only had it for about three months or so, and did not have two gigabit devices until my WHS showed up just over a week ago.

After I get this switch, do you guys see any downside to having the TrendNet router still in line, between the switch and cable modem? Basically the "lowest" tier would be all of my house wiring coming into this new switch, which would then be connected to the TrendNet router for any Internet communication as well as communication with any wireless devices. I can't imagine this would be an issue, as the switch should know that any inter-gigabit communication should not be going out the port to the router. This also would allow me to use DHCP server, etc, on the router still.

Thanks for your suggestions!

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Well basically anything going through that box might still have problems. Since that's your router AND 11n access point, that's pretty much anything going out or coming in from the internet. Also anything going to or from your wireless devices.

Ok I'm also going to address some of your ideas which you had. Don't switch the WRT54G to the WAN port unless you want to create yet another subnet and deal with NAT and routing to your main network. As I understand it, your GbE works if you do not plug in any 100Mb devices, so you can also consider removing/upgrading the older devices. If this ends up costing more than a new Gb switch though, it would not make sense.

It does sound like your router has problems with different line speeds on different ports, which is not typical behaviour for a switch. Even a speed sensing hub should be able to do better than this, as all devices fall back, but not to 250kbps unless there really is a device out there asking for this speed (seems unlikely). I won't speculate on the reason, since I have no experience with it, but the way to avoid the problem seems to be get all your devices off those Gb ports except the one line necessary to connect it to the rest of your network. If that still doesn't cure your problem... well just try it out and we'll see.

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All -

Thanks again for the inputs.

All seems to be well at this point. All of my wired jacks in the house are coming into the switch that I just purchased, a D-Link DGS-2208. This includes my two gigabit devices, as well as the WRT-54G (wired via its LAN port) which is at 100M. Also connected to the switch is the same TrendNet TEW-639GR router ... which itself is plugged in (via its WAN port) to the cable modem. So basically the PC or WHS have several hops out to the Internet (switch->router->cable modem). This seems to have solved all of my problems, as it would appear the switch is "keeping things local" and not talking to this problematic router unless necessary. So I am very happy ... WHS <-> PC transfer speeds are in the 35 MBps (280 Mbps) range. Not exactly 90% of theoretical (as seems to be true of 100M speeds) but I'm not going to complain here.

Also, for what it's worth these devices are primarily running with dynamic IPs, with the DHCP server residing on the (problematic) router. However, after they've first talked and gotten their IPs, it would appear that the switch (being a child to the router) does not need to check in with the router ... as cskenney mentioned it clearly remembers who's on what port and does not involve the router/DHCP server.

Thanks again for all of your help ... I think I've gained a lot of knowledge from experiencing this problem, I remember dealing with these things back in the 10M hub days. I guess things just got too easy and could be taken for granted. Apparently the TrendNet guys - via their last e-mail - are looking into things as well and (hopefully) may release a firmware fix if it's possible.

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