My Sniffer Isn't Seeing VLAN, 802.1q, or QoS Tagged Frames
Content Type: Maintenance & Performance | Article ID: 000005498 | Last Reviewed: 02/11/2025
Support Knowledge Base
What am I seeing?
My sniffer is not seeing VLAN or QoS tagged frames.
How do I fix it?
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- In Windows*
To allow tagged frames to pass to your packet capture software, add a registry dword and value, or change the value of the registry key. The driver used impacts the registry change required:
Adapter Driver Registry Key e1g, e1e, e1y MonitorModeEnabled e1c, e1d, e1k, e1q, e1r, ixe, ixn, ixt MonitorMode Note - To understand which driver to use, see How do I identify my wired Ethernet adapter and driver version?
- Drivers included in Windows might not include support for promiscuous mode. This registry entry is only supported on Intel drivers.
Place the new key (dword) at:
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}\00nn
Where nn is the physical instance of the network port where you want to capture the VLAN tags. ControlSet001 might need to be Current Control Set or another 00x number.
Caution
Changes to the registry can disable your system. Have a skilled technician make the changes to the registry. This change is only for promiscuous mode/sniffing use. When creating or changing registry dword MonitorModeEnabled, set the dword value to one of the following:
- 0—disabled (Do not store bad packets, Do not store CRCs, Strip 802.1Q vlan tags)
- 1—enabled (Store bad packets. Store CRCs. Do not strip 802.1Q vlan tags)
When creating or modifying registry dword MonitorMode, set the dword value to one of the following options:
- 0—disabled (Do not store bad packets, Do not store CRCs, Strip 802.1Q vlan tags)
- 1—enabled (Receive bad/runt/invalid CRC packets. Leave CRCs attached to the packets. Do not strip VLAN tags and ignore packets sent to other VLANs as per normal operation.)
Note You must restart Windows for the registry change to take effect. - In Linux*
By default, the driver in promiscuous mode does not strip VLAN tags.
To strip VLAN tags: Load the kernel supplied 802.1q module. This step automatically enables the Intel Networking hardware offload capabilities to offload VLAN tag stripping and insertion. For support and information on loading the 802.1q module, contact your distribution.
Your capture software is responsible for enabling promiscuous mode in your driver. If the driver is not in promiscuous mode, the packets are dropped or ignored because of the bad type/len field.