Broadcom bge and 802.1Q vlan tags

Gleb Smirnoff glebius at
Tue Oct 12 07:02:19 PDT 2004

On Tue, Oct 12, 2004 at 10:36:27AM +0200, Roub?cek Zdenek (T-Systems PragoNet) wrote:
R>  I have run into a problem with my Broadcom NIC (Dell LATITUDE D600). I am not able to detect 802.1Q tags on incoming interface with ethereal or tcpdump. All incoming packets seems like they are not coming through trunk but as native ETH frames, ie. the vlan tag is missing, probably removed before being passed to tcpdump?
R> No I have not tested NIC's behaviour on 4.X, but I is working with linux (2.6.something kernel probably?)
R> Any ideas what to modify or set so I can detect vlan_tag would be very apreciated.

As Ruslan already mentioned, it is impossible to turn off hardware VLAN
stripping in bge driver.

A patch to stop tagged frames to come on trunk interface is like this:

@@ -701,13 +657,16 @@
         * see if the device performed the decapsulation and
         * provided us with the tag.
-       if (ifp->if_nvlans &&
-           m_tag_locate(m, MTAG_VLAN, MTAG_VLAN_TAG, NULL) != NULL) {
+       if (m_tag_locate(m, MTAG_VLAN, MTAG_VLAN_TAG, NULL) != NULL) {
                 * vlan_input() will either recursively call ether_input()
                 * or drop the packet.
-               KASSERT(vlan_input_p != NULL,("ether_input: VLAN not loaded!"));
+               if (vlan_input_p == NULL) {
+                       /* vlan(4) is not loaded, discard frame */
+                       m_freem(m);
+                       return;
+               }
                (*vlan_input_p)(ifp, m);

Totus tuus, Glebius.

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