Slow MacOS gigabit, but fast Windows gigabit. Huh?

WilliamG

macrumors G3
Original poster
Mar 29, 2008
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Seattle
So I've got a 2014 5K iMac, a 2014 Mac mini, a 2017 MacBook Pro, and my iPad Pro 2018 over USB Type-C gigabit. All devices are wired.

For some reason, all these devices have plummeted in terms of speeds to my CenturyLink gigabit fiber connection. I cannot for the life of me figure it out. My Windows PCs all have 930Mbit down/up.

The Macs? All around 450Mbit down, but the full 930Mbit up.

Has something changed in MacOS lately that would cause this? I'm completely befuddled, so any help would be appreciated. I've tried a single connection directly to the modem/router, bypassing all switches etc, and it's still not fast enough. Local speed between devices on the network is the full gigabit speed, too - it's just the speed over WAN that's not acceptable.

All help appreciated. I've spent hours on this today.
 

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keysofanxiety

macrumors G3
Nov 23, 2011
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25,262
Which version of MacOS? Also are they all from a Time Machine backup or fresh installs?

You can try create a new user account on one of the Macs to isolate if the problem may be software related.

Not that it helps, but I had the opposite problem on my Windows desktop. 450-ish down, 950 up, yet the Mac (15” 2012 cMBP) would be gigabit up and down. This was regardless which drivers were installed on W10.

It seems an unusual coincidence we’d see a similar problem on different systems... but it’s certainly not unheard of (albeit pretty undiagnosable) if this is any consolation.
 

WilliamG

macrumors G3
Original poster
Mar 29, 2008
9,100
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Seattle
Which version of MacOS? Also are they all from a Time Machine backup or fresh installs?

You can try create a new user account on one of the Macs to isolate if the problem may be software related.

Not that it helps, but I had the opposite problem on my Windows desktop. 450-ish down, 950 up, yet the Mac (15” 2012 cMBP) would be gigabit up and down. This was regardless which drivers were installed on W10.

It seems an unusual coincidence we’d see a similar problem on different systems... but it’s certainly not unheard of (albeit pretty undiagnosable) if this is any consolation.
Fresh installs. Mojave. Tried the new user thing earlier. No dice.

Really at a loss...
 

keysofanxiety

macrumors G3
Nov 23, 2011
9,536
25,262
Fresh installs. Mojave. Tried the new user thing earlier. No dice.

Really at a loss...
All power sleep mode stuff disabled? PRAM reset (can’t hurt)?

I’m just throwing guesses, no idea really. Sorry. Do you have boot camp on any of the Macs — if so, is it better there?
 

WilliamG

macrumors G3
Original poster
Mar 29, 2008
9,100
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Seattle
All power sleep mode stuff disabled? PRAM reset (can’t hurt)?

I’m just throwing guesses, no idea really. Sorry. Do you have boot camp on any of the Macs — if so, is it better there?
Yeah no dice on any of it. No power saving stuff.
 

KonaBlend

macrumors member
Oct 18, 2008
32
4
The Macs? All around 450Mbit down, but the full 930Mbit up.

Has something changed...
Could be something in your Century link router has changed either by you, or by update (automatic?) from your provider. Taking a wild stab here, is jumbo frames enabled on your router? Long shot, configure one of the desktop Mac to use jumbo frames and see if that helps downstream.
 

WilliamG

macrumors G3
Original poster
Mar 29, 2008
9,100
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Seattle
All power sleep mode stuff disabled? PRAM reset (can’t hurt)?

I’m just throwing guesses, no idea really. Sorry. Do you have boot camp on any of the Macs — if so, is it better there?
Also tested with a completely fresh install of High Sierra on a USB3 SSD, in case Mojave was the issue. Still no luck.

This is insane.
[doublepost=1547778388][/doublepost]
Could be something in your Century link router has changed either by you, or by update (automatic?) from your provider. Taking a wild stab here, is jumbo frames enabled on your router? Long shot, configure one of the desktop Mac to use jumbo frames and see if that helps downstream.
Jumbo frames enabled on the client side does make a small difference, actually. Bizarrely, I see decent speeds when speedtesting in Firefox on one of the Macs. I just don't get it. Chrome/Safari/Speedtest app = poor speeds.

I need to figure out how to check my Edgerouter ER-4 to see if Jumbo Frames is enabled there.
 
Last edited:

KonaBlend

macrumors member
Oct 18, 2008
32
4
Jumbo frames enabled on the client side does make a small difference, actually. Bizarrely, I see decent speeds when speedtesting in Firefox on one of the Macs. I just don't get it. Chrome/Safari/Speedtest app = poor speeds.
if it's only a small difference then jumbo-frames is unlikely to be related to your 50% downstream issue.
 

WilliamG

macrumors G3
Original poster
Mar 29, 2008
9,100
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Seattle
if it's only a small difference then jumbo-frames is unlikely to be related to your 50% downstream issue.
This is true. I just can't figure out what's going on.

I'm currently using an Edgerouter ER-4. I even put back the original Zyxel router, and directly connected one of my Macs to it - ruling out any cables, switches etc. Still poor download.
[doublepost=1547779523][/doublepost]
Could be something in your Century link router has changed either by you, or by update (automatic?) from your provider. Taking a wild stab here, is jumbo frames enabled on your router? Long shot, configure one of the desktop Mac to use jumbo frames and see if that helps downstream.
Nothing has changed at any point in the router. Haven't touched it. Also, - I mentioned later - I even switched back to the original CenturyLink-provided router just to be SURE.

This is going to make me insane. I have no idea how to fix this. :(
 

KonaBlend

macrumors member
Oct 18, 2008
32
4
This is going to make me insane. I have no idea how to fix this. :(
rule stuff out. unplug everything from your LAN except for your iMac and router. if your router also has extra gig LAN ports, plug your mac right into it. unplug other lan switches, and computers. temporarily disable WiFi on your router.

also download source. is it certain mac's are using the same IP that windows boxes are for downstream? possible somehow the win boxes and mac boxes have differing DNS configurations leading to different IP used.

also; IPv4 vs IPv6; i have no idea about ISP, but what is IPv6 config on mac vs. windows. maybe there's a diff w.r.t. performance with your ISP.
 

WilliamG

macrumors G3
Original poster
Mar 29, 2008
9,100
2,559
Seattle
rule stuff out. unplug everything from your LAN except for your iMac and router. if your router also has extra gig LAN ports, plug your mac right into it. unplug other lan switches, and computers. temporarily disable WiFi on your router.

also download source. is it certain mac's are using the same IP that windows boxes are for downstream? possible somehow the win boxes and mac boxes have differing DNS configurations leading to different IP used.

also; IPv4 vs IPv6; i have no idea about ISP, but what is IPv6 config on mac vs. windows. maybe there's a diff w.r.t. performance with your ISP.
I did rule everything out. Directly connected to router - same issue. IPs are mapped so definitely no conflicts there. DNS config is a possibility, but I didn't set anything on Windows or MacOS, so not sure there.

I believe everything is IPv4 on both. At least the IPs line up with IPv4.
[doublepost=1547782892][/doublepost]My neighbor just got CenturyLink fiber gigabit, last week. Going to run over there and test my devices there... Will update a bit later.
 

KonaBlend

macrumors member
Oct 18, 2008
32
4
I believe everything is IPv4 on both. At least the IPs line up with IPv4.
[doublepost=1547782892][/doublepost]My neighbor just got CenturyLink fiber gigabit, last week. Going to run over there and test my devices there... Will update a bit later.
more spitballing here. verify the netmask for your mac and router (on LAN side) are identical
 

WilliamG

macrumors G3
Original poster
Mar 29, 2008
9,100
2,559
Seattle
more spitballing here. verify the netmask for your mac and router (on LAN side) are identical
Yep. No concerns there.
[doublepost=1547785219][/doublepost]Took my iPad with USB Type-C -> gigabit adapter over to the neighbor. Speeds were still not good. Is it possible CenturyLink did something to the connection to cause this issue JUST for Macs? I wouldn't even know where to start with customer service...
 

WilliamG

macrumors G3
Original poster
Mar 29, 2008
9,100
2,559
Seattle
I'm at a loss here.

So, to recap:

Performance over LAN is spot on: 940Mbit between all systems.

Performance over the WAN is perfect on Windows-based systems: 940Mbit up/down.

Performance over the WAN on all my Macs = ~450Mbit down/940Mbit up.

When I connected a USB 3.0 Gigabit adapter to the 2014 iMac - that resolved the issue immediately. However, it made no difference on the 2014 Mac mini, for some reason.

NOTE: The Network adapter inside the 2014 Mac mini and 2014 iMac is the same:

Broadcom 57766-A1:

So, I borrowed a 2018 i5 Mac mini, fresh install, and that has the SAME network card in it! And it too has the same download issue. However, connecting the USB 3.0 gigabit adapter to it SOLVES the issue.

So what's going on here? This makes literally no sense to me, and I cannot figure it out. Do Macs just no longer work properly with CenturyLink fiber gigabit connections?
 

KonaBlend

macrumors member
Oct 18, 2008
32
4
I'm at a loss here.

So, to recap:

Performance over LAN is spot on: 940Mbit between all systems.

Performance over the WAN is perfect on Windows-based systems: 940Mbit up/down.

Performance over the WAN on all my Macs = ~450Mbit down/940Mbit up.

When I connected a USB 3.0 Gigabit adapter to the 2014 iMac - that resolved the issue immediately. However, it made no difference on the 2014 Mac mini, for some reason.
nuts... I can understand your frustration! How about this, try comparing ifconfig output for built-in vs. USB adapter. maybe there is something in there, besides the MAC address, that is different? Post both results if you can (if the IP is not public).

 

WilliamG

macrumors G3
Original poster
Mar 29, 2008
9,100
2,559
Seattle
nuts... I can understand your frustration! How about this, try comparing ifconfig output for built-in vs. USB adapter. maybe there is something in there, besides the MAC address, that is different? Post both results if you can (if the IP is not public).


OK, here's the info of the BUILT-IN Ethernet on the iMac 2014:

en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500

options=10b<RXCSUM,TXCSUM,VLAN_HWTAGGING,AV>

ether xx:xx:xx:xx:xx:xx:

inet6 xxx:xxxx:xxx:xxxx:%en0 prefixlen 64 secured scopeid 0x5

inet 192.168.0.6 netmask 0xffffff00 broadcast 192.168.0.255

nd6 options=201<PERFORMNUD,DAD>

media: autoselect (1000baseT <full-duplex,flow-control,energy-efficient-ethernet>)

status: active


And the USB 3.0 Ethernet (which remember, solves the issue on my 2014 iMac and 2018 Mac mini - but NOT the 2014 mini:

en6: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500

options=4<VLAN_MTU>

ether xx.xx.xx.xx.xx.xx

inet6 xxx:xxx:xx:xxx:xxx%en6 prefixlen 64 secured scopeid 0x14

inet 192.168.0.191 netmask 0xffffff00 broadcast 192.168.0.255

nd6 options=201<PERFORMNUD,DAD>

media: autoselect (1000baseT <full-duplex>)

status: active




Now, before you ask, I have played with those flow-control settings - every permutation in fact, with no success.
 

KonaBlend

macrumors member
Oct 18, 2008
32
4
Now, before you ask, I have played with those flow-control settings - every permutation in fact, with no success.
clarification, does permutations include disabling energy-efficient-ethernet? Sounds plausible that if the adapter and switch are being overzealous in efficiency it could hurt performance. Also you have tried a nice short and proven LAN cable?
[doublepost=1548050746][/doublepost]also there is a "-v" option for ifconfig -- might show a few more bits for comparison
 

WilliamG

macrumors G3
Original poster
Mar 29, 2008
9,100
2,559
Seattle
clarification, does permutations include disabling energy-efficient-ethernet? Sounds plausible that if the adapter and switch are being overzealous in efficiency it could hurt performance. Also you have tried a nice short and proven LAN cable?
[doublepost=1548050746][/doublepost]also there is a "-v" option for ifconfig -- might show a few more bits for comparison
I’ll try the -v.

I can say I changed nothing. With gigabit for 2+ years and all of a sudden this happens. Just very peculiar. No software updates either to any systems in the time it went funky.

And yes I tried every variant of flow-control on/off, energy efficiency on/off.

This is one case where I’m 100% sure I changed nothing. And I never even touch my wife’s 2017 MacBook Pro, and it’s behaving the same as my systems. The whole thing is flat-out weird.
 

WilliamG

macrumors G3
Original poster
Mar 29, 2008
9,100
2,559
Seattle
I ran the test -v, but don't see anything unusual. I genuinely think CenturyLink has done something over the WAN to cause issues for Macs. I just don't know how or why.
 
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