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Invalid source MAC address used? #678

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autoditac opened this issue Feb 21, 2023 · 2 comments · May be fixed by #683
Open

Invalid source MAC address used? #678

autoditac opened this issue Feb 21, 2023 · 2 comments · May be fixed by #683

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@autoditac
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Hi,

we have discovered that the Hyper-V VMSwitch (we are using this for VLAN segmentation on our test setups) drops all packets coming from SOEM.

After playing around a bit it seems that Hyper-V VMSwitch does not like the src MAC address SOEM is using by default 01:01:01:01:01:01 since it is set to being multicast, which doesn't really make sense for a source address:

image

After we manually changed the packet to being unicast (the MAC being rewritten to 00:01:01:01:01:01) and retransmitting it, Hyper-V VMSwitch correctly forwards the packet:

image

Is this intended that way and a misunderstanding on our side or is this a bug in SOEM?

Thanks and kind regards :-)
@ArthurKetels
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Contributor

SOEM was never tested to be used in a VLAN environment. But as you see, the solution to your problem is very simple.

You can set any source MAC address you like. There is one requirement, the U/L bit must not be set as that is used to differentiate outgoing from returning packets. EtherCAT slaves set the U/L bit to signal they have passed the ESC.

The original intend to set the I/G bit was to be able to use switches as star topology elements. It did work on a few old switches, but nowadays this is very rare to succeed. So consider it legacy.

@nt15
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nt15 commented Mar 6, 2023

https://github.com/OpenEtherCATsociety/SOEM/blob/master/oshw/erika/nicdrv.c
and
https://github.com/OpenEtherCATsociety/SOEM/blob/master/oshw/rtems/nicdrv.c

are setting U/L bit

I can make a fix to this and have sent signed Contributor License Agreement, let's see if i get access :)

@nt15 nt15 linked a pull request Mar 7, 2023 that will close this issue
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Using unicast MAC address as source address nt15/SOEM
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@ArthurKetels @autoditac @nt15