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USB Adapter with packet drops

asked 2020-05-10 10:21:23 +0000

JasMan gravatar image

updated 2020-05-10 10:25:58 +0000


I've bought a USB 3.0 10/100/1000 Ethernet adapter with an AX88179 chip from UGREEN ( as capture device for my Win10 client. It's connected to a span port of an Netgear GS108Tv3 switch.

When I did the first capture I realized that there are a lot of "Previous segment not captured" messages in different TCP streams. So I started a second capture on the client side interface to compare the captures. The capture of the client looked fine. No errors or drops. But the capture of the USB adapter showed about 200 "Previous segment not captured" messages in one minute of 200 kbit/s traffic.

I've already did the following troubleshootings:

  • Changed driver of US Adapter to original ASIX drivers -> same behaviour
  • Checked adapter with another client -> same behaviour
  • Started capture with the internal on-board-LAN port of my client on the same span port -> no "Previous segment not captured" messages. Conclusion: Span port is fine:
  • USB adapter works fine as LAN interface. 952 Mbit/s throughput (iPerf3) without unusual error frames.
  • Disabled all energy-saving and offloading options of USB adapter -> same behaviour
  • Captured with dumpcap.exe. -> same behaviour. The summary at the end says "No lost packets"

Now I'm not sure if the adapter has a defect, or if something blocks the missing packets. Use anybody else the adapter from UGREEN? Or has anybody an idea what's going wrong here?

Thank you. Jas

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During your ipref test, was the interface in promiscuous mode? That seems to be a differentiator here.

Jaap gravatar imageJaap ( 2020-05-10 11:21:28 +0000 )edit

All captures I did were done in promiscuous mode, so also the capture during the iPerf test.

JasMan gravatar imageJasMan ( 2020-05-10 11:33:46 +0000 )edit

I often see issues with USB adapters and traffic collection. Sometimes they pull in all traffic OK, other times they drop specific streams (say all multicast or traffic from a specific IP). I find that dedicated tools such as Profishark from Profitap do this sometimes too, so it's not just cheap USB adapters. I'm sorry I don't have a solution but I also find resetting the adapter often solves the problem for a short period of time. I have come to rely on builtin ethernet ports as much as possible for critical data traffic collection.

Bob Jones gravatar imageBob Jones ( 2020-05-10 12:59:27 +0000 )edit

I agree that there are some adapters which are having problems to capture all the traffic. But due to my experiences, and also as you've commented, they're missing all packets of a special type or pattern then. In my case only some single packets of different streams get dropped. When I compare the capture from the client (which contains all packets) and the one from the USB adapter, the missing packets are having no common pattern. Looks more like something is blocking or discards the packets.

JasMan gravatar imageJasMan ( 2020-05-10 13:33:03 +0000 )edit

I was able to test another adapter with AX88179 chipset from Unplugable (USB3-E1000), and it has the same issue. So no hardware issue. But I wonder that nobody else noticed this behaviour. As I know the AX88179 chipset is recommend to easily capture VLAN tags in Windows.

I will now use my on-board LAN interface as capture interface, and the USB adapter as network connection.

If anybody can recommend a USB adapter as capture device including VLAN tags for Windows, please let me/us know :-)

JasMan gravatar imageJasMan ( 2020-05-15 20:40:31 +0000 )edit

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answered 2020-05-15 22:41:10 +0000

Bob Jones gravatar image

The following USB adapters pick up VLAN tags in Windows10 at least:

  • USB 0bda:8153/RTL 8153
  • USB 0bda:8152/RTL 8152 (TPLink)
  • USB 2357:0601/RTL 8153
  • USB 0b95:772b/ASIX 88772B

Does not work for me to get VLAN tags in Win10:

  • USB 0bda:8152/RTL 8152 (Some no name vendor)

All my Intel adapters pick up VLANs too in Windows if I make the required registry changes.

I still would not use any of these USB adapters for any type of long term / critical capture requirement but I make extensive use of them in a lab environment where I can validate the traffic profile is as expected prior to relying on the data they provide.

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I bought a TP-Link UE300 adapter with RTL8153 chipset and tested it.

When I had disabled "Priority & VLAN" in the adapter settings to get the VLAN tags, I saw again a huge packet loos during the capture. After hours of testing I realized that only full-MMS-size packets get lost. So I enabled the jumbo-frame feature and that solved the packet loos issue. I never heard or read that I've to enable jumbo-frames when I want to capture VLAN tags. Is this a known behaviour?

I tried it also with the ASIX adapter but it didn't solved the issue.

JasMan gravatar imageJasMan ( 2020-06-11 14:44:13 +0000 )edit

I have these adapters and just tested this with ping and my results match yours. Looks like max MTU is 1500, and with VLAN disabled, the 4-byte vlan header counts as data now. I never noticed this before - I guess my typical data flows don't utilize large frames very often.

Bob Jones gravatar imageBob Jones ( 2020-06-11 16:29:15 +0000 )edit

Thank you @Bob Jones for testing. I appreciate your effort. And I'm glad to read, that's not only me again who's having this behaviour :)

JasMan gravatar imageJasMan ( 2020-06-11 21:56:11 +0000 )edit

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Asked: 2020-05-10 10:21:23 +0000

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Last updated: May 15 '20