Справочник Пользователя для SonicWALL 5.8.1

such as DSCP. SonicOS Enhanced has the ability to DSCP mark traffic after classification, as 
well as the ability to map 802.1p tags to DSCP tags for external network traversal and CoS 
preservation. For VPN traffic, SonicOS can DSCP mark not only the internal (payload) packets, 
but the external (encapsulating) packets as well so that QoS capable service providers can 
offer QoS even on encrypted VPN traffic.

The actual conditioning method employed by service providers varies from one to the next, but 
it generally involves a class-based queuing method such as Weighted Fair Queuing for 
prioritizing traffic, as well a congestion avoidance method, such as tail-drop or Random Early 
Detection. 

The following sections detail the 802.1p standard and DSCP QoS. These features are 
supported on SonicWALL NSA platforms.

SonicOS Enhanced supports layer 2 and layer 3 CoS methods for broad interoperability with 
external systems participating in QoS enabled environments. The layer 2 method is the IEEE 
802.1p standard wherein 3-bits of an additional 16-bits inserted into the header of the Ethernet 
frame can be used to designate the priority of the frame, as illustrated in the following figure:

.

TPID: Tag Protocol Identifier begins at byte 12 (after the 6 byte destination and source 
fields), is 2 bytes long, and has an Ethertype of 0x8100 for tagged traffic. 

802.1p: The first three bits of the TCI (Tag Control Information – beginning at byte 14, and 
spanning 2 bytes) define user priority, giving eight (2^3) priority levels. IEEE 802.1p defines 
the operation for these 3 user priority bits.

CFI: Canonical Format Indicator is a single-bit flag, always set to zero for Ethernet 
switches. CFI is used for compatibility reasons between Ethernet networks and Token Ring 
networks. If a frame received at an Ethernet port has a CFI set to 1, then that frame should 
not be forwarded as it is to an untagged port. 

VLAN ID: VLAN ID (starts at bit 5 of byte 14) is the identification of the VLAN. It has 12-bits 
and allows for the identification of 4,096 (2^12) unique VLAN ID’s. Of the 4,096 possible 
IDs, an ID of 0 is used to identify priority frames, and an ID of 4,095 (FFF) is reserved, so 
the maximum possible VLAN configurations are 4,094.

802.1p support begins by enabling 802.1p marking on the interfaces which you wish to have 
process 802.1p tags. 802.1p can be enabled on any Ethernet interface on any SonicWALL 
appliance.

Bytes

802.11q VLAN Tag

Protocol ID
(x8100 for 802.1q tags)

Bits

802.1p

VLAN ID

CFI

preamble

DA

SFD

SA

VPID TCI

Len

LLC

Data

FCS

7

1

6

6

16

3

1

12

2

2

2

46-1500

4