Re: [PATCH pve-docs v2 1/1] network/sdn: update and clean up VLAN information

["Thomas Ellmenreich" <t.ellmenreich@proxmox.com>]

On Tue Oct 20, 2026 at 3:54 PM CEST, Stefan Hanreich wrote:
> On 10/20/26 8:45 AM, Thomas Ellmenreich wrote:

[snip]

>> +[[vlan_common_issues]]
>> +Common Issues
>> +^^^^^^^^^^^^^
>> +
>> +.Issue: Configuring VLAN on interface that is member of bridge
>> +
>> +It's not recommended to configure a VLAN on an interface that is a member of a
>> +bridge. Doing so will "blackhole" all traffic of that VLAN on the bridge.
>
> Might need a more specific example so this becomes clearer? It's hard to understand
> otherwise imo.

If I understand correctly, the example [0] you mention further down would be
an instance of 'blackholing' the traffic. Perhaps I could mention that
example here instead of creating a separate point for it.

Is this assumption correct?

>> +
>> +.Issue: Limited number of tags when VLAN offloading to NIC
>> +
>> +Certain NIC's, only support VLAN offloading only for a reduced number of tags.
>> +In these cases it is best to either reduce the VLAN tag range on the bridge or
>> +disable offloading altogether. The exact problems that can arise depend on
>> +the exact hardware used.
>
> There are two other pitfalls I can think of that can occur when configuring
> VLANs directly on top of physical interfaces:
>
>
> When using a VLAN on the host (often the management VLAN) and starting a guest
> with a network device that has the same VLAN tag set, connectivity to the host is
> lost on that VLAN after starting the guest.
>

[0]: v

> e.g.:
>
>  # NIC that carries the VLANs
>  iface nic1 inet manual
>  
>  # management VLAN
>  auto nic1.1337
>  iface nic1.1337 inet static
>          address 10.133.7.10/24
>  
>  # non vlan-aware bridge
>  auto vmbr1
>  iface vmbr1 inet manual
>          bridge-ports nic1
>          bridge-stp off
>          bridge-fd 0
>
> and then a guest:
>
>  net0: name=eth0,bridge=vmbr1,hwaddr=BC:24:11:86:69:F3,tag=1337,type=veth


[snip]