Slow Internet speed when HomePlug combined with router

networking router internet cable-modem powerline-networking

7,152

What happens if you plug both powerline devices into the same plug strip AND turn off every circuit breaker in the house except the one powering this circuit? (i.e. Eliminate all possible sources of powerline noise.) If you find this resolves your speed issue then turn breakers back on one at a time until you find which has the noise source (and it may not just be one, but you get the idea). The difference between protocols I expect is exactly that... other protocols have better error correction than TCP.

7,152

Cocowalla

Updated on September 18, 2022

Comments

Cocowalla almost 2 years

I'm using HomePlug AV2 600 devices to connect upstairs with downstairs (router is downstairs). A check with iperf shows bandwidth of ~100Mbps, and data transferred on the local network from downstairs to upstairs is transferred at about that speed. Good times.

But when I try to access the Internet from upstairs, maximum throughput is only 40Mbps. Bad times.

If I try from downstairs, I get the full 80Mbps that my Internet connection allows. This is really puzzling, as I know the HomePlugs are working faster than that for local data.

Here's what my setup looks like (the router is connecting to a fibre modem using PPPoE, everything has gigabit ports, and all testing was using wired connections):

                         +----+                           
                         | PC |                           
                         +-+--+                           
                           |                              
                           |                              
                       +---+----+         +----------+    
                       | Switch +---------+ HomePlug |    
                       +--------+         +-----+----+    
                                                |         
    Upstairs                                    |         
+-------------------------------------------------------+
    Downstairs                                  |         
                                                |         
  +-------+ PPPoE +-----------------+     +-----+----+    
  | Modem +-------+ Wireless Router +-----+ HomePlug |    
  +-------+       +-----------------+     +----------+

If I connect to the router downstairs (wired), then it works great:

                       +--------+         +----------+    
                       | Switch +---------+ HomePlug |    
                       +--------+         +-----+----+    
                                                |         
    Upstairs                                    |         
+-------------------------------------------------------+
    Downstairs                                  |         
                                                |         
  +-------+ PPPoE +-----------------+     +-----+----+    
  | Modem +-------+ Wireless Router +-----+ HomePlug |    
  +-------+       +-----------------+     +----------+    
                           |                              
                           |                              
                        +--+-+                            
                        | PC |                            
                        +----+

If I wire the downstairs HomePlug straight to the modem, and setup a PPPoE connection from the Windows 7 machine upstairs, it also works as expected:

                         +----+                           
                         | PC |                           
                         +-+--+                           
                           |                              
                           |                              
                       +---+----+         +----------+    
                       | Switch +---------+ HomePlug |    
                       +--------+         +-----+----+    
                                                |         
    Upstairs                                    |         
+-------------------------------------------------------+
    Downstairs                                  |         
                                                |         
  +-------+            PPPoE              +-----+----+    
  | Modem +-------------------------------+ HomePlug |    
  +-------+                               +----------+

I've also tried plugging the HomePlugs in right next to each other on the same floor, and get the same poor results:

    Downstairs                                          

  +-------+ PPPoE +-----------------+     +----------+    
  | Modem +-------+ Wireless Router +-----+ HomePlug |    
  +-------+       +-----------------+     +-----+----+    
                                                |
                                                |
                               +----+     +-----+----+    
                               | PC +-----+ HomePlug |    
                               +----+     +-----+----+

So the issue is only there when connecting to the Internet through both HomePlugs and the router, and only affects WAN traffic. I've tried replacing the router with a newer model, but get the same result. I also tried replacing the HomePlugs with a different brand (first tried Solwise, now Devolo).

I've also tried creating a PPTP VPN tunnel between my upstairs computer and the downstairs router - and this does inexplicably gives me the full bandwidth I would expect. But this relies on using DD-WRT on my router - and it's very flakey.

I'm at a loss, so any help would be much appreciated!

Spiff almost 10 years

What speed do you get from the Upstairs PC, through upstairs switch, both HomePlugs, through the wireless router's LAN-side switch, to a machine plugged into a LAN port on the wireless router? Now take the downstairs machine and plug it into the WAN port of the wireless router instead of the modem (e.g. use static IP addresses to set up a point-to-point Ethernet WAN link; be sure to leave NAT on, but turn PPPoE off); what speed do you get from that WAN-connected machine all the way to the upstairs PC?
Cocowalla almost 10 years

@Spiff for the 1st part, speeds are ~100Mbps. I hadn't thought of trying the 2nd part, which seems like a good idea. But I can't get it to work in DD-WRT.. even tho I set a static IP, the downstairs machine still ends up with a default IP address (169.x.x.x or whatever)
Spiff almost 10 years

Your router won't serve DHCP out the WAN port. You have to give your WAN-connected machine a static IP on the same subnet as the static IP you gave your router, and set its default gateway to the static IP you gave the WAN port of the router.

Cocowalla almost 10 years

I guess this should have been a comment, rather than an answer? In the test where I plugged in right next to each other, I did have everything else switched off. What protocols are you referring to? I've only been testing using TCP.
Cocowalla almost 10 years

Just a note, SMB is a layer-5 protocol that operates on top of TCP.
Cocowalla almost 10 years

I've tried a variety of protocols, so I don't believe this to be the issue. If I try SFTP or SCP on the LAN over the 2 HomePlugs, it's very fast. If I try it wired directly to the router, to a cloud server, it's very fast. If I try it over the 2 HomePlugs to a cloud server... only max 40Mbps again.
Tyson almost 10 years

I take it that the GUI for your devices don't show correctables and uncorrectables, that alone would give you a much better picture.
Cocowalla almost 10 years

No, it doesn't. Are there any other tools that I can use?
Cocowalla almost 10 years

As I mentioned at the end of my question, I did also try Solwise HomePlugs, with the same results. I'm in the UK with FTTC - do you have any more information about the BT issues, as I can't see why there would be an issue there?
Joey almost 10 years

Oops I read through your question a good couple of times but missed the last part. Here are four links: community.bt.com/t5/BT-Infinity-Speed-Connection/… community.bt.com/t5/BT-Infinity-Speed-Connection/… community.bt.com/t5/BT-Infinity-Speed-Connection/… avforums.com/threads/…
Joey almost 10 years

By the way, are you GYRE? community.plus.net/forum/index.php?topic=126114.0
Cocowalla almost 10 years

@Joey no, I'm not :) I did come across that thread before tho, and tried fiddling with the MTU settings to no avail
Cocowalla almost 10 years

None of these seem to apply to me as I don't have any issues with my sync speed (~80Mbps, as I'm only ~300m from the cabinet), and LAN speeds over the HomePlug are great (most the of gripes seem to be about HomePlug speed in general, but they work well in my relatively new house)
tiktak over 9 years

What do you mean by better error correction than TCP? And more importantly, what would you substitute it with? It's not a choice for users to make.
Cocowalla almost 8 years

Actually, if I setup a PPTP VPN between my upstairs computer and the downstairs router (still using the homeplugs), I inexplicably get all available bandwidth (I'll update my original question to note this). My homeplugs have a built-in filtered socket, and the modem is already plugged into this. Both of these seem to go against your hypothesis.
Aron almost 8 years

@Cocowalla oh.. That sounds like an MTU mismatch then. The MTU on LAN is typically 1500 whilst ATM which is what PPPoE/A needs to add a few bytes for the wrapping. It sounds like PMTUD is failing with the home plugs installed. Can you try lowering the MTU on you PC's network card?
Cocowalla almost 8 years

I had thought the same, and tried playing around with MTU settings, but to no avail :(