[src/trunk]: src/share/man/man4 Explain how exactly tagged packets are proces...

[bad <bad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/e3f17eb78c74
branches:  trunk
changeset: 811363:e3f17eb78c74
user:      bad <bad%NetBSD.org@localhost>
date:      Mon Oct 26 22:18:57 2015 +0000

description:
Explain how exactly tagged packets are processed.
While here remove a bit of non-techref wording and assume that people know
what VLANs are good for..

XXX: pullup-7, pullup-6

diffstat:

 share/man/man4/vlan.4 |  44 +++++++++++++++++++++++++++++++++++++-------
 1 files changed, 37 insertions(+), 7 deletions(-)

diffs (80 lines):

diff -r 8b0b067ecb8c -r e3f17eb78c74 share/man/man4/vlan.4
--- a/share/man/man4/vlan.4     Mon Oct 26 19:41:19 2015 +0000
+++ b/share/man/man4/vlan.4     Mon Oct 26 22:18:57 2015 +0000
@@ -1,6 +1,6 @@
-.\"    $NetBSD: vlan.4,v 1.31 2010/12/16 18:29:47 wiz Exp $
+.\"    $NetBSD: vlan.4,v 1.32 2015/10/26 22:18:57 bad Exp $
 .\"
-.\" Copyright (c) 2000 The NetBSD Foundation, Inc.
+.\" Copyright (c) 2000, 2015 The NetBSD Foundation, Inc.
 .\" All rights reserved.
 .\"
 .\" This code is derived from software contributed to The NetBSD Foundation
@@ -27,7 +27,7 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd December 16, 2010
+.Dd October 26, 2015
 .Dt VLAN 4
 .Os
 .Sh NAME
@@ -43,9 +43,8 @@
 802.1Q Virtual Local Area Networks
 .Pq Tn VLAN .
 This supports the
-trunking of more than one network on a single network interface.
-This is particularly useful on routers or on hosts which must be
-connected to many different networks through a single physical interface.
+trunking of more than one network on a single network interface by using
+802.1Q tagged and untagged frames.
 .Pp
 To use a
 .Nm vlan
@@ -58,7 +57,9 @@
 .Tn VLAN
 from any others
 .Pc
-and physical interface associated with the
+and
+.Pq parent
+physical interface associated with the
 .Tn VLAN .
 This can be done by using the
 .Xr ifconfig 8
@@ -75,6 +76,35 @@
 .Dv SIOCSIFVLAN
 arguments.
 .Pp
+Packets sent through a
+.Nm
+interface are tagged with the VID and passed to the parent interface for
+transmission.
+Tagged packets received on the parent interface are passed to the
+.Nm
+interface with the corresponding VID associated with the parent interface.
+Packets sent directly through the parent interface are transmitted as
+untagged frames.
+Untagged frames received on the parent interface are handled by the
+parent interface.
+Tagged frames received on the parent interface with a VID of 0 and an
+EtherType of IP or IPv6 are processed on the parent interface.
+Tagged frames received on the parent interface for which no
+.Nm
+interface with a matching VID exists are dropped and counted as
+.Dq unknown protocol .
+.Po
+These are displayed by the
+.Xr ifconfig 8
+.Fl -v
+option.
+.Pc
+.Pp
+If the 
+.Nm
+pseudo-device is not configured in the kernel only packets tagged with a
+VID of 0 are processed.
+.Pp
 To be compatible with other
 .Tn IEEE
 802.1Q devices, the