I am asking this here because I have never seen anything like this before and I did not even know it was possible, but it is definitely happening.
Here is the topology. I have a Netgear WNDR3700v4 router running DD-WRT firmware. It is connected by a 50 foot CAT-6 cable to a Netgear GS-105 5-port switch.
Also connected to the router is my Mageia-based workstation.
The switch has two connections to my NAS. One connection is to the Asus motherboard and handles data transfers. The other connection is directly to the RAID controller card, enabling me to monitor and control it directly.
Also connected to this switch, presently, is an Acer computer running Windows Vista. I connected it because I am loading a bunch of old DVDs onto my NAS, and the Acer DVD reader seems to do a better job of reading these than the one on my workstation (which needs to be replaced).
I encountered some difficulty getting the Acer to open the Video share on my NAS and, rather than figure it out (this is Vista, after all), I have the Acer opening a share on my workstation...which it did without difficulty. I then am doing a "click and drag" on the Acer to move files from the DVDs to the share on my workstation. On my workstation, I review the files, sometimes rename them, then ship them via an NFS connection to the Video share on the NAS, which is their final resting place.
So here is what happens.
When the Acer is transferring files in this fashion. the link light on both the router and the switch, for the connection between them, goes out intermittently. The lights come on briefly whenever the Acer is making a transfer, then goes back out as the Acer is loading up the next chunk of data from the DVD. While this link light is out, the link is down. I cannot communicate with my NAS from my workstation, pings fail, the log on my workstation tells me that my iscsi link is down and my NFS link is down.
When the Acer is not transferring, the link light for the connection is on solidly and apparently reliably.
The link light between the Acer and the switch remains on solidly throughout; it is only the connection between the router and the switch that goes up and down.
At first I thought this was a defective cable; when I move the cable to different ports on the router and the switch, the problem follows the cable. But I eventually noticed the correlation between what the Acer was doing and what the link was doing; the link comes alive long enough for the Acer to transfer a block of data, then goes dead again.
Now, sometimes the link DOES remain alive when the Acer is buffering more data. This, too, happens at intermittent intervals and when it happens I can communicate with the NAS and everything works.
It sure looks like Vista is doing something. But what? And why? I was not aware that this Netgear switch could even be managed; there are no docs I have seen that say so, but clearly its links can be raised and lowered remotely. Possibly DD-WRT in the router is doing it, but I see no configuration information to suggest it is even capable of that and if it IS doing it, how does it know to restore the link when the Acer wants to transfer a block of data? The data comes through at regular intervals, including during the times when the link remains alive, so I can't say that the Acer is transferring whenever DD-WRT brings the link back up.
Is there a software or signalling failure mode so severe that the solution is a hard reset of the link?
I do not plan to have the Acer continually available on this link; I pulled it out of the closet for this job and can't wait to put it back in the closet. But the fact that this happens is troubling; I don't understand it. Anyone have any ideas?