Ethernet Port Issue

[RobMHTown]

Hi All - so I have an interesting issue.    I have a CM1000 cable modem, Gig internet via Xfinity.   I use a Linksys Velop system and have a Netgear GS316 unmanaged switch which feeds interenet into multiple devices.

My setup currently works this way:   Modem -> Linksys Velop Parent -> Switch -> Devices

One of my devices (a mac computer) is hooked into one of the ethernet cables that runs through the house and into the switch.     When I plug the device into the ethernet, there is a slow blinking of the green lights on the switch.   The device tries to make a connection, but then drops the connection after a second.

I had initially thought this was a poor cable somewhere in my walls.    However, I was trying to fix and ended up running the cable from the switch through a Linksys access point sitting next to the switch and when I plugged in the device (which is all the way on the other side of the house), it worked!   Not sure why putting an access point in the middle cures this.   Connection speed is ~90mbps which is below the gig speed, so trying to figure out how to access via the switch only (no AP between device and switch).

Any thoughts?

[antinode]

> I had initially thought this was a poor cable somewhere [...]

   You may have been right.

> [...] However, [...]

   Any hardware change could affect some marginal condition in other
hardware -- flakey cable, weak receiver/transmitter, ...  One device
might erroneously negotiate a 1000MHz link, and then fail when it tries
actual communication at that speed, while another device might fail to
negotiate a 1000MHz link, and then work better at a lower speed.

> [...] Connection speed is ~90mbps which is below the gig speed, [...]

   Gigabit speed uses all four pairs in a cable; slower speeds use only
two.  On the Mac, System Preferences > Network : Ethernet <n> >
Advanced... : Hardware should tell you the physical link speed.

> [...] trying to figure out how to access via the switch only (no AP
> between device and switch).

   I'd try to move the computer to within range of a known-good cable,
and, if that works, then start adding questionable hardware until the
failure (re)appears.

   I recently spent far too much time on the phone with a friend whose
Windows system seemed to be confused about the existence of his
Ethernet/Internet connection.  LEDs were flashing happily everywhere,

but the Internet was always out of reach.  In desperation, he hauled the
computer to within different-cable-range of the network switch, swapped

cables, and every ill was instantly cured.