Thunderbolt Ethernet Bridge very slow

Question

Thunderbolt Ethernet Bridge very slow

My 2012-era MacBook Air is connected to a 2012-era iMac via a Thunderbolt cable. The iMac contains a Thunderbolt-Ethernet bridge which in theory should allow the MBA to (1) participate in extremely fast file transfers with the iMac and (2) access the Internet and LAN without the use of additional ethernet cabling or WiFi.

Both operations work, but with a catch: Sending packets from the MBA to any computers on the LAN *other* than the iMac, or to any computers on the Internet, is incredibly slow. Receiving packets works as expected. Sending a file from a server on the LAN to the MBA, for example, is very fast, and downstream speed tests on SpeedTest.net max out my Internet connection at 60Mbps. But all traffic in the other direction is ridiculously slow; Traffic from the MBA to machines on the LAN or the Internet moves at around .08Mbps.

The only other post that mentions this problem is here: http://apple.stackexchange.com/questions/118855/thunderbolt-bridged-with-etherne t-gives-poor-performance?rq=1

...but it was unanswered. Any ideas?

Lester GrimeNose

iMac, Mac OS X (10.7)

Posted on Jun 19, 2015 8:05 PM

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Answer 1

Jul 20, 2017 10:05 PM in response to Lester GrimeNose

For those who want to connect by Apple's Thunderbolt Ethernet adapter, but not necessarily by bridging...

In System Prefrences > Network : Unless you are specifically trying to connect two computers via Thunderbolt Bridge, don't use the "bridge" interface option. Instead connect using "Thunderbolt Ethernet."

If you don't see this option in the left side panel, select the + button below it and you will be prompted to select a new interface for a drop down menu. You should see a huge jump in speed (5 Mbps to 110 in my case - though in theory I should get even faster speeds).

Unfortunately we have not used the Thunderbolt Bridge interface for long-term pipelines at my work, so I don't know how or if the speed can be increased.

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Answer 2

Jun 21, 2015 6:49 AM in response to Lester GrimeNose

I am getting exactly the same problem. My iMac has speeds of 10mb down & 1.2 upload but the Mac Air is down to <2mb download with a 0.5 upload if i sue the thunderbolt cable. If I disconnect the Mac Air I get the same speeds as the iMac.

Definitely being slowed down by the thunderbolt connection - but why? Seen a lot on this with no answers.

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Answer 3

Eric Root

Level 10

684,603 points

Jun 21, 2015 10:40 AM in response to Lester GrimeNose

Basic troubleshooting.

Thunderbolt Connection Problems

Thunderbolt Device not Working

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Answer 4

Jun 21, 2015 11:01 AM in response to Eric Root

Thanks but made no difference. Found a You Tube vid that helps me setup a manual DHCP and that seems to have cured it.

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Answer 5

Jun 21, 2015 3:25 PM in response to mick kelly

@mick: Interesting. The problem is most certainly on the machine that hosts the Thunderbolt bridge. That's the iMac in our scenarios. I say this because traffic successfully passes between the MBA and iMac at an extremely high rate. It's only when the MBA's outbound traffic goes beyond the iMac that the bottleneck occurs.

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Answer 6

Jun 23, 2015 5:05 AM in response to mick kelly

@mick: can you tell me how you cured it? Or please provide a link to that youtube video?

I have the same problem:

Three iMacs hooked up to the Thunderbolt ports of a MacPro, everything is smooth and fast – except for traffic that's upstream beyond the MacPro.

I got it working yesterday for a short period of time but I can't replicate it. I applied DHCP with manual address and changed it back to manual and then it worked. When it worked, the bridge also could obtain an IPv6 address from the router, normally it doesn't obtain one (don't know if that even matters because I mainly need IPv4 to work). I suspect that some things were set up by Bonjour that are not set when doing ist manually but …

… like I said, I can't replicate it.

thanks a lot!

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Answer 7

Jun 23, 2015 7:33 AM in response to stolz-krechting

Another technique that works is to use Internet Connection Sharing. Share the Thunderbolt-Ethernet bridge on the host (the iMac in my case) and the client machines suddenly will be able to transmit packets beyond the host at a reasonable rate.

This approach is unworkable for me, however, because it creates a double-NAT. The Internet lives on 66.66.660/0, the LAN including the iMac host and other servers on 192.168.1.0/24, and now the MacBook Air on 192.168.2.0/24. This is problematic because certain MBA applications I use require the use of broadcast traffic to interact with other machines on the LAN. Those applications will obviously fail with the MBA and LAN now existing on two separate network segments.

The bottom line is that creating a network using a Thunderbolt-Ethernet bridge just isn't possible right now. It's too buggy. The bridge is helpful for rapid data transfer between exactly two computers tethered with a Thunderbolt cable, and that's about it.

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Answer 8

cdhw

Level 4

3,588 points

Jun 23, 2015 7:41 AM in response to Lester GrimeNose

All the constraints you have are not clear to me, but if you could use one of these:

http://store.apple.com/us/product/MD463LL/A/thunderbolt-to-gigabit-ethernet-adap ter

I strongly recommend it. I've found these gadgets work great and are a snip at $29.

C.

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Answer 9

Jul 28, 2015 6:46 AM in response to Lester GrimeNose

Hi,

I re-test Thunderbolt bridging in every version of OS X and it is still way too inconsistent.

NOTE: I have yet to test 10.10.4 - maybe a job for this weekend!

Even between new MacBook Pro 13" Retina and a new MacBook Air, the speed fluctuates from the low 50MB/s to 800+ MB/s.

A lot of people have tested this as the new poor man's SAN - especially for shared storage for video editing.

Intel announced Thunderbolt networking for PCs recently so it seems to be a case of Apple needing to fix the virtual NIC drivers for the Thunderbolt bridge.

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Answer 10

cdhw

Level 4

3,588 points

Jul 28, 2015 6:57 AM in response to Desktop Guy

It is not particularly easy to generate and receive data at the speeds needed to test Thunderbolt. Are you sure you are not just measuring the speed of your disk caches. 800MB/s (i.e. 6.4Gbps) is quite fast.

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Answer 11

Jul 28, 2015 7:05 AM in response to cdhw

Hi,

The MacBook Air and MacBook Pro both sustain 1GB/s throughput to the SSD.

This is verified with iPerf, DiskSpeedTest and Helios LANtest.

People over at CreativeCow see similar fluctuations for Thunderbolt Bridges running to Areca and Lacie RAIDs which both run between 600MB/s and 800MB/s.

Issue is with Apples driver - the same Thunderbolt interface performs rock solid to attached RAIDs - only difference is networking code.

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Answer 12

Dec 8, 2015 10:10 AM in response to Lester GrimeNose

I have found a solution so that the uploads are fast again (use this where the uploads are slow, in your example on the MacBook Air):

sudo sysctl -w net.inet.tcp.tso=0

… that disables the "TCP segmentation offload".

the downside to this is that this degrades the thunderbolt performance (but it is still faster than 1Gb Ethernet).

leaving the segmentation on (=1) but disabling the sending checksumming:

sudo sysctl -w net.link.generic.system.hwcksum_tx=0

… has the same effect – uploads are fast again but the top speed of thunderbolt is slower.

I think I would rather disable the segmentation than the checksumming but I am not a real "network guy", so that's just guessing.

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