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weird phantom traffic on my new linksys switch!?

K

kirbysdl

Junior Member
Last night, my week-old Linksys 8-port switch went haywire. At the time, there were two machines connected to it. It was registering insane traffic (blinking activity LEDs) on both machines, but a tcpdump came up empty. I disconnected one machine from the switch, and the remaining ACT LED was still going strong (again, no traffic on tcpdump).

I forgot exactly what I tried at that point, but it at least included cycling power on the switch, performing /etc/rc.d/init.d/network restart on the Unix box, reconfiguring TCP on the windows box, and testing all the cables and NICs involved with a laptop.

Long story short: it works now, but this is very disturbing. Is this something that is probably the fault of the switch's, or did something else go wrong? If it is a problem with the switch, I guess I will return it. Would you recommend staying with Linksys or going with 3com (the one I'm looking at is around 40% more expensive)?

http://www.3com.com/products/en_US/detail.jsp?tab=features&pathtype=purchase&sku=3C16791-US http://www.linksys.com/products/product.asp?grid=34&scid=31&prid=36

Thanks!
 
Next time you have trouble, disconnect BOTH PCs - all cables in fact. If at that point you still see activity on the switch, it's bad and should be replaced. Infant death in particular is a known failure mode of all electronics.

Linksys is not the highest quality switch manufacturer out there, but they're not bad. All switches have some failure rate. I don't believe that 3Com will be that much better. A lot of people have Linksys switches that work for years.
 
Yeah I just have 2-3 machines on right now. I got it with room to expand in mind. A crossover could work otherwise. =P

Hmm ok. Thing is, it's not infant death. The switch appears to work now! Someone suggested it might be due to heat, but I doubt that. It has plenty of clearance, and the ambient temp can't be that bad. Very strange. Thanks for the suggestions. Any other ideas?
 
cmetz has the right idea. diconnect all when it happens next see if its bad.


otherwise its just the 2 pc communicating with each other. is it slowing down the communcatins at all?
 
not noticeably. When it came, i clocked the transfer between arbitrary ports at around 90Mbit ... so not bad.

The computers can communicate with little trouble over a crossover, so i doubt it's the computers themselves that are at fault, but who knows.
 
so the switch is still working fine (90 mb) when this happens?

sounds like everythign is a-ok then.


you know it coudl be a NIC going haywire and sending out lots of information thus the switch is correctly showing traffic.


the real test would be throwing a 3rd computer on there and seeing if the traffic casues problems.
 
I had a similiar problem with a Linksys Router. It showed the same symptoms as your Linksys switch. It eventually died shortly after that.
 
martind1: actually, no i'm not getting any traffic when it goes haywire. first post said the tcpdump was returning nothing... hence my alarm.

nightowl: hmm ok i guess i better return that thing then =P

anyone in IT have extensive experience with these kinds of unmanaged switches? I'm looking for recommendations...
 
Maybe the traffic isn't TCP.

Do you have IPX, Appletalk, or any other protocols at that level enabled? Some of them have "heartbeats" where they send a broadcast packet a couple times a second.
 
Sorry if I wasn't clear. While there was traffic according to the activity LEDs, no traffic could actually get through. My DHCPing Windows machine went from a 192.168.x.x to 169.254.x.x. So the switch be scrood. It actually did the same thing again tonight. RMA, here I come!

Any ideas what I should replace it with?
 
Originally posted by: kirbysdl
Sorry if I wasn't clear. While there was traffic according to the activity LEDs, no traffic could actually get through. My DHCPing Windows machine went from a 192.168.x.x to 169.254.x.x. So the switch be scrood. It actually did the same thing again tonight. RMA, here I come!

Any ideas what I should replace it with?
Click to expand...

same model?

-edit- a whole lot of conditions could cause what you're seeing, one of which is a malfunctioning switch.
 
Originally posted by: glugglug
Maybe the traffic isn't TCP.

Do you have IPX, Appletalk, or any other protocols at that level enabled? Some of them have "heartbeats" where they send a broadcast packet a couple times a second.
Click to expand...

Download a packet sniffer (like Ethereal), and find out what the traffic is. Then you'll know, and won't have to guess.
 
It turns out heat was the problem. I'm not sure why, but the switch was overheating. There was a faint smell of burning electronics and the case of the switch was very hot to the touch (think CPU heatsink). That was obviously causing the routing malfunction, phantom traffic and burning lights, disconnected machines, etc. I replaced it with a 3com, which is doing fine for the moment. Thanks for the help in diagnosing!
 
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