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Hi all,

I have just changed my internet provider, which now requires the use of VLAN 100 on the WAN interface to work properly. I have configured it correctly, but I do not get any connectivity at all, I am not even getting an IP address from my provider.

Trying to figure out what was happening, I ran a simple tcpdump :

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tcpdump -i vlan00.100 -n -vvv 'udp and (port 67 or port 68)'and boom: internet connectivity is now back, either on opnsense (which correctly now gets IPv4 and IPv6 from my provider) or other clients on my LAN (I have 2 other LAN VLANS behind).

The second I stop the tcpdump command, connectivity falls down and nothing works again.

I'm using the following nic adapters:

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igb0@pci0:1:0:0: class=0x020000 rev=0x03 hdr=0x00 vendor=0x8086 device=0x1539 subvendor=0x8086 subdevice=0x0000
    vendor     = 'Intel Corporation'
    device     = 'I211 Gigabit Network Connection'
    class      = network
    subclass   = ethernet

And all hardware offloads are turned off (CRC, TSO, LRO) ; VLAN hardware filtering is set to Disable.

First guess: tcpdump is putting my WAN interface in promiscuous mode, thus solving some kind of "driver" issue (igb). But before actually putting WAN in promiscuous mode, I wonder if this issue is something already known or documented? I have not find any clear indication so far.

Thanks for your help!

PS: running opnsense 25.7.10