How can a laptop's dock bring down my network?

[badbob001]

My Dell Latitude 5400 laptop has a WD19 dock with an ethernet jack. I connect it to my home network, which has a few unmanaged switches. When the laptop is on, no issues. But when the laptop is off, after a few minutes, all traffic from the closest network switch is blocked.

Connectivity is instantly restored if I:

• Unplug Ethernet cable from dock or unplug the same cable from the switch port
  or
• Turn on laptop

Could it be related to the IEEE 802.3az energy efficient feature of these switches? Or some compatibility issue with devices that set their ethernet connection to a low-power/speed mode? The lights on the switch are still blinking so it's not as if it dies or hung.

About a month ago, I bought a few Netgear 16-port unmanaged switches (GS316) and life was great until one of them mysteriously lost all connectivity and needed a powercycle to fix. I replaced the switch but then another switch had the same issue a week later. I then just returned all the switches and got similar switches from TP-Link (TL-SG116). I thought the issue was resolved but now this happens.

I JUST got the laptop/dock today so could the netgear failure be due to another device going into low-power mode? I only thought of the dock as the cause because it's the only new thing added to the network today. This is all very confusing.

Maybe I should switch back to my older non-green switches (fewer ports).

 

[MichaelCG]

Do you have the local Ethernet jack of the laptop connected as well? Kind of sounds like you have a loop somewhere on your network and spanning tree is going into blocking mode.


Sent from my iPhone using Tapatalk

 

[ColinTaylor]

I'd agree with @MichaelCG , it sounds like you have created a network loop somewhere. If you are sure there are no loops in your network topology then examine the behaviour of the laptop. It's WiFi adapter should be disabled when it is plugged into the dock, check that it is. If the problem only happens when the laptop is in standby perhaps there's a bug whereby it is re-enabling the WiFi adapter when it shouldn't. Try manually disabling all WiFi on the laptop and seeing if the problem goes away.

 

[MichaelCG]

To note....I also use a WD19 as well and have no issues. WiFi should have no impact here....I would "guess" more risk related to having Ethernet enabled on the laptop and the dock and possibly MAC cloning going on causing issues with the same MAC showing up on multiple ports freaking the switch out.

Do you have SONOS connected to these switches? What else is on the network that has more than just a single wired interface...potentially wireless (like Sonos)?

 

[badbob001]

Would two switches connected to each other with more than one cable count as a network loop? If so, I then I'll need to audit my cabling to see if I have multiple interconnections.

Some computers have two nics but I only have one connected. I do have a couple of synology nas with multiple nics.

nas 1:

• two nics connected to lan with each having separate ip.
• one nic directly connected to other nas with 169.254.*.* private ip

nas 2:

• one nic connected to lan with ip.
• one nic directly connected to the other nas (mentioned above).

Other:

• many alexa echos (wireless)
• many wyze cameras (wireless)
• many firetv (wired)
• three asus ac-68/ac-86 access points (wired, not using aimesh)
• computers with wired and wifi connections (usually not both on at the same time)

 

[ColinTaylor]

Would two switches connected to each other with more than one cable count as a network loop?

Possibly. At the very least it's an invalid network design that should be avoided as the behaviour of the switches would be unpredictable. The only exception would be if you were using link aggregation on each switch to bond multiple cables.

nas 1:

• two nics connected to lan with each having separate ip.
• one nic directly connected to other nas with 169.254.*.* private ip

nas 2:

• one nic connected to lan with ip.
• one nic directly connected to the other nas (mentioned above).

I assume that's a typo for NAS 1, "two nics connected to lan..."? That should be the same as NAS 2, "one nic connected to lan...".

When you say one nic on each NAS is directly connected to the other as 169.254.x.y do you really mean directly connected? They are not connected via a switch are they?

 

[badbob001]

I assume that's a typo for NAS 1, "two nics connected to lan..."? That should be the same as NAS 2, "one nic connected to lan...".

I connected the second nas nic for minor reasons:

• Have a second ip to ping in case the primary ip fails to help identify where the network failure is.
• Clients can connect to the second ip with different samba credentials from the first.

When you say one nic on each NAS is directly connected to the other as 169.254.x.y do you really mean directly connected? They are not connected via a switch are they?

Directly connected means nic to nic; no switch involved. But mentioned in case there is some sort of bridging magic I'm not aware of.

 

[badbob001]

Do you have the local Ethernet jack of the laptop connected as well? Kind of sounds like you have a loop somewhere on your network and spanning tree is going into blocking mode.

The laptop nic was not used until after I discovered the issue with the dock.

 

[badbob001]

Possibly. At the very least it's an invalid network design that should be avoided as the behaviour of the switches would be unpredictable. The only exception would be if you were using link aggregation on each switch to bond multiple cables.

Any tools like Wireshark that can easily identify if the network has any loops? Trying to avoid lots of disconnecting a device from the network and then running to the corresponding switch to see which light goes off...

 

[ColinTaylor]

Any tools like Wireshark that can easily identify if the network has any loops?

I can't think of any. You'd really need to have a managed switch with port mirroring capability to stand a chance of seeing what's happening.

It's a bit strange that it only seems to be triggered by this one device when it's in standby. As you appear to be able to recreate the problem on demand you could plug another PC into the same switch and see if the problem is preceded by any unusual broadcast traffic.

 

[coxhaus]

I think without us seeing it, it will be hard to trouble shoot. May I suggest you start over with all connections and whiteboard everything. You may be able to figure it out. At least you don't have hundreds of connections.

If you screw up a Lagg port you can cause network issues. You could first go around and unplug all Lagg ports to 1 connection. This way they will still run. If you have any devices with 2 LAN ports plugged into them then remove 1 connection so you are down to 1 connection. Once everything is reduced to 1 port per device start trouble shooting again. If this requires rebuilding then you will find the problem as you go 1 step at a time.

It can be software in the switches so look at the settings. IS your router reduced to 1 port also, it should be.