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I have a pair of powerline ethernet boxes set up to connect the top floor of my house to the rest of the home network.

Periodically, I've found that the network in the rest of the house becomes extremely slow. Disconnecting the ethernet from the powerline ethernet appears to fix the problem.

I originally thought it was a problem with the powerline ethernet boxes, and replaced them with new boxes. However, the problem has reoccurred with the new boxes, which makes me think that it's not the boxes, but something else.

Unfortunately, I don't know what that would be.

My home network is rather complicated, with several switches. Yet the networking disruption appears to occur across the entire network.

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My guess would be a routing loop - ie you have 2 ethernet connections between points.

Assuming you don't have spanning tree enabled (its really only available on more expensive managed switches), My first step in diagnosing the problem would be to look at how much the lights are flickering on the various switches, then systematically disconnect wires one at a time until the problem goes away. Alternatively, cable trace everything and do a diagram.

It is, I guess, possible that the issue is something else - maybe your neighbour is also using powerline and the devices are getting mixed messages on default gateways to use etc.

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  • If it is intermittent the cabling loop isn't permanent. Somebody is plugging in stuff whenever it happens (or powering on an extra switch which has 2 connections to the rest of the LAN). Powerline from neighbors merging your network to theirs (as your last line describes) is extremely rare (not impossible though), but just electrical interference from Powerline at the neighbors is far more likely and can also do weird things. Some Powerline adapters use spanning-tree themselves, which may contribute to the problem too. Some unmanaged switches react to spanningtree (they shouldn't do that).
    – Tonny
    Dec 19 '20 at 9:08
  • @tony surely interference would only affect the speed of the power line connected devices?
    – davidgo
    Dec 19 '20 at 9:52
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    No. With enough interference the powerline adapters loose connection and try to re-sync over and over again. This creates a lot of broadcast traffic that gets into the whole LAN slowing everything down. It also results in partially transmitted (corrupt) ethernet frames being send to the rest of the LAN. Most switches will not propagate these further, but some really cheap unmanaged switches deal badly with that and send them on and/or clog up their own buffers with them. All togehter the impact can be far worse than what you would expect.
    – Tonny
    Dec 19 '20 at 10:30
  • Pretty sure it's not a routing loop, as things work OK most of the time. My switches are pretty cheap and unmanaged. The switch connected directly to the powerline adapter is a D-Link DGS-2205 that I picked up about a decade or so ago.
    – Eric Brown
    Dec 19 '20 at 23:12
  • After a bit more experimenting, I suspect the problem is a routing loop. The problem appears to be that the mesh WiFi is also connected to the powerline network. When the powerline network is running well, the mesh WiFi uses that as its backhaul, and everything's good. When the powerline network is not working well, the mesh WiFi switches over to one of its peer nodes, which sends the traffic from the powerline network (everything) back over the WiFi connection, and that causes the routing loop.
    – Eric Brown
    Jan 5 at 22:35

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