* 3-bit field <= VPT(VLAN Priority Tags)

* Static VLANs = port-based VLANs


CoS Value(0~7)

used to classify the packets by mapping packets to one of the output "queues".


Queue (1~4)

Packets arriving untagged are assigned a default VPT that is set on a per port basis

When no rules are defined, the traffic containing the predefined packet field (CoS or DSCP) is mapped according to the relevant trust modes table.



PCP    Priority    Acronym    Traffic types
1    0 (lowest)    BK    Background
0    1    BE    Best Effort
2    2    EE    Excellent Effort
3    3    CA    Critical Applications
4    4    VI    Video, < 100 ms latency and jitter
5    5    VO    Voice, < 10 ms latency and jitter
6    6    IC    Internetwork Control
7    7 (highest)    NC    Network Control


Class - Queue mapping

class      Queue

0,3        2         # 因為 PCP 的 1 才是要高低 Priority
1,2        1
4,5        3
6,7        4

Dell 2824 Setting

CoS Mode(E/D)
Trust Mode (802.1P/DSCP)

Determines which "packet fields" to use for classifying packets entering the device.
When no rules are defined, the traffic containing the predefined packet field (CoS or DSCP) is
mapped according to the relevant trust modes table.

Traffic not containing a predefined packet field is mapped to "best effort".

CoS (802.1P) — The output queue assignment is determined by the IEEE802.1p VLAN priority tag (VPT) or
by the default VPT assigned to a port.

QoS Queue Settings(Scheduling):

Strict Priority - Ensures that time-sensitive applications are always forwarded through an expedited path.

Weighted Round Robin — Ensures that a single application does not dominate the device forwarding capacity.

T (Trunk)

The interface is a member of a VLAN. All packets forwarded by the interface are tagged. (The packets contain VLAN information)

| Host | ---- |SW port| -- forwarded packets --> |SW port| ---- |Host|


The interface is a VLAN member. Packets forwarded by the interface are untagged.


The interface is denied membership to a VLAN.


The interface is not a VLAN member.

Example of the VLAN port table.

Ports:    1  2  3  4  5  6  7  8
VLAN 1:   U  B  B  B  B  B  B  B
VLAN 2:   T  U  U  U  U  B  B  B
VLAN 3:   T  B  B  B  B  U  U  U

在 VLAN 2 時, Port 2 無 tag 的 package 入, Port 1 出的 packet 係有 tag 的. Port 1 有 TAG 的 package 入, Port 2 出係無 tag 的

Frame Type - Packet type accepted on the port. Possible values are:

– Admit Tag Only — Only tagged packets are accepted on the port.
– Admit All - Both tagged and untagged packets are accepted on the port.

Ingress filtering - discards packets that are destined to VLANs of which the specific is not a member.

Linux set vlan tagged

lsmod | grep 8021q

modprobe 8021q

入改 /etc/modules


# Create eth0.X
vconfig add eth0 X

vconfig add eth1.2

Added VLAN with VID == 2 to IF -:eth1:-

ifconfig eth1.2 up

# re-mapped the default priority 0 to egress priority 7
vconfig set_egress_map eth0.X 0 7

cat /proc/net/vlan/eth1.2

eth1.2  VID: 2   REORDER_HDR: 1  dev->priv_flags: 1
         total frames received            0
          total bytes received            0
      Broadcast/Multicast Rcvd            0

      total frames transmitted           60
       total bytes transmitted         4310
Device: eth1
INGRESS priority mappings: 0:0  1:0  2:0  3:0  4:0  5:0  6:0 7:0
 EGRESS priority mappings:

就算 "ifconfig eth1.2 down" 後, 這 file 仍會存在並且更新數據 !

# The default skb-priority is 0
set_egress_map  [vlan-name]      [skb_priority]   [vlan_qos]
set_ingress_map [vlan-name]      [skb_priority]   [vlan_qos]


Remove a vlan

  • rem                # Removes

i.e. vconfig rem eth1.2

# 檔案 /proc/net/vlan/eth1.2 會消失了



ifconfig eth0.222 up

ifconfig eth0.222 netmask


auto eth0.222
iface eth0.222 inet static
        vlan-raw-device eth0



Control Panel > Network and Internet > Network and Sharing Center > Change Adapter settings.

NIC > Properties  > Advanced > Priority and VLAN Enabled