Table 22: How the switch uses the ToS configuration
Outbound port
ToS option:
802.1p (value = 0 - 7)
Differentiated services
IP packet sent out an
untagged port in a
VLAN
Depending on the value of the
IP Precedence bits in the
packet’s ToS field, the packet
will go to one of eight
outbound port queues in the
switch. See the table in
For a given packet carrying a ToS codepoint that
the switch has been configured to detect:
• Change the codepoint according to the
configured policy and assign the 802.1p
priority specified for the new codepoint in
the DSCP Policy Table (Differentiated
Services Codepoint (DSCP) mapping).
• Do not change the codepoint, but assign the
802.1p priority specified for the existing
codepoint in the DSCP Policy Table
(Differentiated Services Codepoint (DSCP)
mapping).
Depending on the 802.1p priority used, the
packet will leave the switch through a queue as
defined in the table in Overview of QoS
settings on page 170.If
No-override
(the
default) has been configured for a specified
codepoint, then the packet is not prioritized by
ToS and, by default, is sent to the “normal
priority” queue.
IP packet sent out an
untagged port in a
VLAN
Same as above, plus the IP
Precedence value (0 - 7) will be
used to set a corresponding
802.1p priority in the VLAN tag
carried by the packet to the
next downstream device. See
the table below.
Same as above, plus the Priority value (0 - 7) will
be used to set a corresponding 802.1p priority
in the VLAN tag carried by the packet to the next
downstream device. Where
No-override
is the
assigned priority, the VLAN tag carries a “0”
(normal priority) 802.1p setting if not prioritized
by other QoS classifiers.
Table 23: ToS IP-precedence bit mappings to 802.1p priorities
ToS byte IP precedence bits
Corresponding 802.1p priority
Service priority level
000
1
Lowest
001
2
Low
002
0
Normal
003
3
Table Continued
Chapter 8 Quality of Service (QoS): Managing bandwidth
effectively
191