DSS usage

Bjørn Mork bjorn at mork.no
Thu May 1 16:41:43 PDT 2014

Bjørn Mork <bjorn at mork.no> writes:

> I think I'll try this out.  I have experimented a bit and found that we
> can avoid the illogical VLAN ID by simply abusing 802.1p for this, i.e
> just use "VLAN 0".

Nope, that's simply not true.  Well, we probably can, but all the
additional magic stuff around vlan_id 0 makes it a hassle. For example,
hardware filters for vlan_id 0 are always added for every netdev:

	if ((event == NETDEV_UP) &&
	    (dev->features & NETIF_F_HW_VLAN_CTAG_FILTER)) {
		pr_info("adding VLAN 0 to HW filter on device %s\n",
		vlan_vid_add(dev, htons(ETH_P_8021Q), 0);

and never deleted:

	/* Take it out of our own structures, but be sure to interlock with
	 * HW accelerating devices or SW vlan input packet processing if
	 * VLAN is not 0 (leave it there for 802.1p).
	if (vlan_id)
		vlan_vid_del(real_dev, vlan->vlan_proto, vlan_id);

OK, forget about abusing 802.1p.  Back to some other vlan_id for IP
session 0.  But I still think this is a simple and functionally
satisfying solution.


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