# Ethernet slow one way?



## zaxcom (Jul 12, 2003)

I have three Macs connected together using a linksys router. Mac 1 and Mac 2 talk to each other just fine and exchange files at about 82Mbps. But Mac 3 has an issue. It is an older 333iMac. When I send files to it I get a consistent 62Mbps, which is fine considering the 5400RPM drive and 66Mhz bus.

But when I try to get files from the iMac it creeps. Maybe 5 or 6Mbps and lots of stalls and hesitation.

I tried using a different port on the router and had no effect. The 100Mbps light on the router is on for all ports.

All three machines are running OSX 10.2.6

Any ideas?

Thanks

Zax


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## Cheryl (Jul 13, 2003)

It could be a number of things.  Check the ethernet cable. It could be damaged or old - old things do break down and run slow (hehehe).  A new ethernet - or a even shorter length may improve things. 

Second idea could be that the older Mac is just slower in processing, you may need more memory installed to speed things up. Or you just need to run a Disk Utility on the machine. Drive 10 is a good one. Do not use Norton on OS X.


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## Zammy-Sam (Jul 13, 2003)

Well, it has definitly nothing to do with your cable. There is no seperated line for upload and download. Fullduplex is using the same line just different timing for up and download. And since you can send files to that one with 62Mbps...
And obviously your system can handle the fast data-transfer. It's a weird problem. Is there any way to check out some kind of advanced options of network-devices and compare? Options like duplex, protocol, timing... I know those from pc.
And one more idea. If you have still some more ports free on your router, try another plug. in worst case I would try to connect two systems directly (without router) and see, how your rates look like. If they are fine, it has something to do with your router.
Let us know


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## zaxcom (Jul 14, 2003)

I have three Macs connected together using a linksys router. Mac 1 and Mac 2 talk to each other just fine and exchange files at about 82Mbps. But Mac 3 has an issue. It is an older 333iMac. When I send files to it I get a consistent 62Mbps, which is fine considering the 5400RPM drive and 66Mhz bus. 

But when I try to get files from the iMac it creeps. Maybe 5 or 6Mbps and lots of stalls and hesitation. 

I tried using a different port on the router and had no effect. The 100Mbps light on the router is on for all ports. 

All three machines are running OSX 10.2.6 

Any ideas? 

Thanks 

Zax


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## Zammy-Sam (Jul 14, 2003)

didn't you post it before or is it just a deja vu I got?


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## Ripcord (Jul 14, 2003)

If you run "netstat -s | grep retransmitted" in the iMac, do you see a large number of packets retransmitted?  If you check immediately before starting a copy and again as soon as it ends, oes the number increase quite a bit?  How much?

Rip


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## Ripcord (Jul 14, 2003)

Otherwise, can you give more details?  Any idea how you're transferring files?  AFP?  CIFS?  What happens if you try FTP?


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## zaxcom (Jul 14, 2003)

Yes, when I try to send the file from the imac to the other machines I get a very high number of retransmitted packets. But when I put the files onto the imac i do not get that problem.

I am connecting using file sharing. Appletalk is turned off.

I also tried using FTP and while it was much slower than file sharing, the results were the same. Up loads very fast, no packets problems. But downloads off the imac were very slow and lots of packets retransmits.


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## Ripcord (Jul 14, 2003)

Actually, in 10/100/1000baseT Ethernet, transmit and receive use different lines, even in half-duplex mode.  Ethernet simply uses old-fashioned CS/CDMA to detect if collisions occurred, even if there's only two devices - an Ethernet NIC and a switch.  This is all weird legacy stuff =)


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## DeltaMac (Jul 14, 2003)

Have you tried a completely different patch cable on this iMac, not just a different hub node?  It's possible there is a flaky ethernet port on the logic board

How about transferring this thread to hardware (or deleting one)?  there are 2 separate threads on this identical problem and this member, the other is already in hardware


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## ScottW (Jul 14, 2003)

Swap out your ethernet cable and see if that does the trick.  Probably a bad cable.


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## zaxcom (Jul 14, 2003)

I ran a test on the cable. I have a very comprhensive cable tester made by Microtest, called a Pentascanner. It reports that all of the lines are fine and there are no problems with the cat5 in any way.

Swapping out would be hard too. it is a 82 foot run through the walls of the house.


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## Ripcord (Jul 14, 2003)

Data is getting lost coming FROM the iMac to your systems.  Since data copies "fine" between your two other systems, this has something to do with your iMac.

It's most likely one of three things:

1)  You have a faulty cable with a poor (or poorly twisted) TX line.  Try replacing with another, good, Cat 5 cable.  Perhaps try a known working one from one of your other systems.
2) NIC going bad in the iMac.  Least likely, and not much you can do except get another logic board or NIC.
3) The switch ports of your Linksys router are set to auto-negotiate speed and duplex, while your NIC in your iMac is set to 100/full duplex.  As a result, the switch cannot negotiate settings with your iMac, and falls back to 100/half, causing a duplex mismatch.  Problem is, this way, packets usually get lost in the OTHER direction, but it still wouldn't be healthy.

Look to see how the iMac is set - run "ifconfig en0" and see what it says next to "media" (not "supported media").  It may make sense to force it to auto-negotiate (Apple calls this "autoselect", which is a bit misleading)

Rip


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## Arden (Jul 14, 2003)

Would putting Airport into the iMac be viable?  You wouldn't have to put the other 2 computers on Airport if they work well together, but you may want to get around the Ethernet problem with the iMac.


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## zaxcom (Jul 14, 2003)

I ran ifconfig and it said it was in full duplex/100. The router also says full duples/100.

The cable tester said the cable was fine. So it may be the NIC. Just to confirm though i am going to make up a new cable and just run it through the house on the floor and see what happens. Either way i am really hosed. A new logic board is expnsive and pulling a new cat5 through the walls will be a major hassle.


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## Ripcord (Jul 14, 2003)

> It reports that all of the lines are fine and there are no problems with the cat5 in any way.



Still, if you're out of other options, try hooking the iMac up to another, good cable and port (I know it's a pain, but I've seen too many cable testers lie to think that's the end of the story).

Rip

*Edit:  I'm not intentionally repeating everything that everyone says, it just takes me a really long time to reply because I'm doing it between commercials and apparently not bothering to hit "refresh" =)


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## Ripcord (Jul 14, 2003)

What model router?


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## zaxcom (Jul 14, 2003)

I have eliminated the router from the equation. I hooked the imac cable directly to the G4 and still had the same problem. I used a crossover cable in between by the way.


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## Ripcord (Jul 14, 2003)

Now, were they both set to autoselect, both set to full duplex, or one set one way, and one set another?  Are you sure you didn't get rid of one problem and introduce another?


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## zaxcom (Jul 14, 2003)

All still set to 100/full duplex. I came up with a solution if it is the cable. Since there are two unused pairs in the Cat5 cable I am going to remake the connectors and use another pair.


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## Ripcord (Jul 14, 2003)

*gets suspicious*

Did you build ALL your cables?


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## Zammy-Sam (Jul 15, 2003)

::ha:: 
I knew it was no deja vu.

http://www.macosx.com/forums/showthread.php?s=&threadid=34528


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## btoneill (Jul 15, 2003)

This sounds like a classic example of what can happen when there is a duplex mismatch. Most likely your Mac is set to half-duplex, and the switch is set to full-duplex.  Can you run 'ifconfig -a' from both the box that is slow, and from a box that is fast? Also, what model is your linksys router/switch?

Brian


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## zaxcom (Jul 15, 2003)

Well I think I have traced the problem. After redoing the cables and not having any improvement I decided to bring the machine downstairs and hook it up with a known crossover cable directly to my main G4.

The problem is still there. So its not the router or the cabling going thru the house. Its the machine itself. I did ifconfig -a and confirmed that all machine are indeed in full duplex/100.

I guess the ethernet port on the imac is messed up. Not much I can do about that though, short of replacing the mother board.


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## sethm (Jul 16, 2003)

I had the exact same problem, and found a solution. It wasn't a duplex mismatch (managed switch so I could see exactly what it was doing), or a bad cable. Force the switch side to 10/full.

My story is here:

http://seth.mattinen.org/main.php?section=aenet


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## zaxcom (Jul 16, 2003)

Unfortunately for me I have no way to force my switch. I am using a Linksys BEFSR41 Router and it does not have any provision I am aware of to control its speed or connection protocols.

I guess my only recourse is to take the iMac back down to OS 9. A real bummer since managing one OS in my small network was so much easier than two.


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## Ripcord (Jul 16, 2003)

Hmmm...  If the interface is faulty, why would running OS 9 make any difference?  Sounds like something is being missed...


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## Ripcord (Jul 16, 2003)

Okay, just re-reading.  If you have no way to force your switch to a certain speed or duplex, how can you be sure that it's running at 100/Full?

Also, forcing your NIC to 10/Full (referring to your other thread in the Networking forum) WILL result in a duplex mismatch if your switch/router is set for auto (which I'm almost positive it is).  If you were going to try anything, I'd say try forcing the NIC to 100/half or 10/half.

Also, changing speeds to 10mbit really shouldn't "solve" the problem, it's just a sign that something else is wrong (usually faulty wiring, or that by changing the setting you actually got rid of another problem, like a duplex mismatch...  Or, like Seth says on his webpage, it could just be a driver issue)

I've also run into some situations where 100mbit (or usually gigabit) systems manage to over-drive the system at the other end, which causes packet loss (either on the NIC, in the driver, or on the switch).  Reducing link speed will avoid the issue, but usually a better solution is to reduce TCP window sizes, application block sizes, or whatever, to "throttle" the machine that's overwhelming.

Seems like this would be opposite in your case as well - the iMac would be the LEAST likely to overdrive.  But then, if it's a possibility and you haven't found the REAL problem, I never eliminate it.


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## zaxcom (Jul 16, 2003)

From what i have read in others posts, this is a known problem with 333 imacs running osx. Sure enough when i rebooted the machine into os9 100 full duplex ran just fine. No erros and full speed in both direction.

I know the machine is in full duplex 100 because the lights on my switch say it is, also ifconfig -a also confirms that the NIC is running at 100/full. Plus I put a monitor on the line and it also confirmed the data rate. The whole problem seems to come down to a bad driver in OSX programming. It causes a massive amount of CRC errors on data transmissions. The imac uses a bmac chipset for ethernet, where most other machines us a gmac chipset. The instructions to this chip are a little different. Appple knows about the problem I have been told, but since this machine is so out of date they have little incentive to rewrite the code for it.


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## zaxcom (Jul 17, 2003)

Well I have one last idea. Since I cant force 10/Full on the iMac by way of any command, I am going to force it by way of a hub. I am going to insert a 10Mbps hub in between the iMac and the Router. That should force the iMac to drop down to 10/Full from 100/Full.

I will let you all know later if it worked.

Zax


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## zaxcom (Jul 17, 2003)

I put a 10Mbps hub in the path and it all works great now. While the speed is limited to about 9Mbps. It is consistant in both directions. No more stalls or CRC errors. Since my cable modem connection is only 2Mbps it really does not matter that the iMac is on a slower port than the other machines.


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## Arden (Jul 17, 2003)

Mazel tov!


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