Gigabit Stepping down to 100mbit, fixed by power cycle, cable switch

[RumorConsumer]

I have this odd thing Ive seen throughout my network, different devices. I even saw it overseas at a house I stayed in. 

I perfectly good gigabit connection somehow starts only transmitting at 100mbit. Link speed just starts reporting 100mbit. Usually if a cable is detected as bad I am pretty sure the spec is meant to downgrade it to 10mbit half duplex. But thats not whats happening. Anybody seen this? Oxidation? Just a normal thing that happens? 

[DarrenOC]

@cmr , you commented on something similar whereby you were seeing same behave which was resolved by swapping out cables?

[cmr]

Indeed @DarrenOC, we have seen dirty contacts or kinked/damaged cables dropping 1Gb connections to 100Mb, and then sometimes fluctuating.  More common on longer cable runs (30m+)

[RumorConsumer]

ok great. figured as much.

[PhilipDAth]

There is also something called EEE (Energy Efficient Ethernet) that allows devices to step down the link speed to save power.  Some printers do this when in power save mode, and some notebooks do this when running on battery.

It is also common for desktops and notebooks when they go into standby mode.

[GIdenJoe]

I usually see Gigabit connections going down to 10Mbps half when a pc goes into sleep mode but they go back up to 1 Gigabit when the device wakes up.

Sometimes you can send the magic packet to let the device wake up and see immediate results.

[BlakeRichardson]

Is the device being used internally or externally?  Could be moisture or dust causing the issue or simply a bad cable. 

[RumorConsumer]

Ive had this happen to connections in bedrooms, outdoors, and basements with non insulated doors to the elements.

[BlakeRichardson]

Hmm, how old is the wiring and what type Cat5, Cat5e etc

[RumorConsumer]

All newer installations. Cat5e and later. One of them had this really thin old Belkin cable and I was like ehhhhh no. I did not install this. There are ethernet cables you can just feel are crap. 

[cmr]

Also be aware of CCA cables they are aluminium cores with a very thin layer of copper on top, never use them unless you don't care about connection integrity

[RumorConsumer]

Jeez got it. I know the STP FTP and all that but this I hadn't heard of. Any easy way to know if you have one by looking at the jacket? 

[cmr]

@RumorConsumer it might say CCA on the jacket like this: