Greetings,
When using AF_PACKET sockets with PACKET_AUXDATA socket option to access
the VLAN TCI information of received frames, I have noticed that the
VLAN information in struct tpacket_auxdata, namely,
- tp_vlan_tci
- tp_vlan_tpid
- TP_STATUS_VLAN_VALID and TP_STATUS_VLAN_TPID_VALID flags
is filled in only when the socket is bound to htons (ETH_P_ALL). If the
socket is bound to any specific protocol, the VLAN information fields in
struct tpacket_auxdata are set to 0 even if the datagram of the specific
protocol was received in an 802.1Q-tagged frame.
As the VLAN tag is being stripped off the frame soon in the receive
path, using PACKET_AUXDATA is the only way for an application over an
AF_PACKET socket to know what VLAN did a particular frame arrive in;
yet, the current behavior forces the application to listen to all
received traffic to get the actual VLAN info.
Is this behavior intentional, or is this lack of VLAN info a bug? I am
running vanilla Linux kernel v4.4.6.
Thanks!
Best regards,
Peter
