Hi All.

I have a test bed which connects a small embedded processor to the LINUX Desktop. The specification of both the hardware are listed down below. With this setup whenever a VLAN tagged frame is sent from the Embedded processor , the VLAN tag ( currently tried with only single tag) seems to be automatically stripped in the Desktop . All untagged packets are received as it is. I am planning to try changing the NIC card on the PC . Before that wanted to check, is this any known issue with centOS LINUX version running on this LINUX machine?

If anyone of you have faced similar issue , please do get back.

Desktop:

Framework# uname -a
Linux terminal_testframework 2.6.32-696.23.1.el6.i686 #1 SMP Tue Mar 13 23:09:35 UTC 2018 i686 i686 i386 GNU/Linux
Framework# cat /etc/centos-release
CentOS release 6.9 (Final)

Realtek NIC Card # ethtool -i eth1
driver: r8169
version: 2.3LK-NAPI
firmware-version: rtl8168e-3_0.0.4 03/27/12
bus-info: 0000:12:00.0
supports-statistics: yes
supports-test: no
supports-eeprom-access: no
supports-register-dump: yes
supports-priv-flags: no


Processor End :

armv7l GNU/Linux 3.4.69

Regards
Umam

You mean that traffic from the ARM computer comes in to the Centos PC via eth1?

Linux doesn’t remove VLAN information from a frame, except if you create a VLAN interface like eth1.1234 for that precise purpose. Are you sure it is not stripped by the switch or whatever other device sits between the two computers?

Yes your understanding is correct. Its a direct connection between the two nodes and there are no devices in between. We have also tried sniffing the output in wire and we see the VLAN tag still intact, so I am pretty sure its the Desktop

Regards
Umam

This is normal. Unless you have the Linux box configured to bridge then its a router and a router decapsulates packets in the network stack before passing it up to be processed. The tag gets left behind with the rest of the L2 frame.

I have downgraded to CentOS 6.4 and retained all the other settings in the configuration file and in the test bed . With this I notice that the VLAN tag does not get stripped in this case. Any idea or reasoning that could explain the difference in observation with lower centOs version.

Thanks
Umam

i am having a similar problem, did you figure out what was causing the VLAN Tag to get stripped off?
Thanks