Filter
Top Products
Quality of Service: Managing Bandwidth More Effectively
Globally-Configured QoS
Comparison of Global IP Type-of-Service Classifiers
Table 6-9 shows the difference in how global IP-Precedence and IP-Diffserv
classifiers are implemented in the switch.
Table 6-9. IP Type-of-Service Classifiers
Outbound Port IP Type-of-Service Classifiers
IP-Precedence Mode IP Differentiated Services Mode
IP Packet Sent Out
an Untagged Port
in a VLAN
Based on the IP Precedence bit set in
a packet’s ToS/Traffic Class field, the
packet is sent to one of eight
outbound port queues in the switch:
1 - 2 = low priority (queue 1, 2)
0 - 3 = normal priority (queue 3, 4)
Based on the DSCP codepoint that the switch has been config-
ured to detect, one of the following actions is taken:
• The codepoint is re-marked according to the configured
DSCP policy and the 802.1p priority currently configured for
the codepoint in the DSCP Policy table (Table 6-8).
• The codepoint is not changed, but the 802.1p priority is
marked with the currently configured value for the
codepoint in the DSCP Policy table.
4 - 5 = medium priority (queue 5, 6)
Based on the new 802.1p priority marking, the packet leaves
the switch through one of the following queues:
6 - 7 = high priority (queue 7, 8)
1 - 2 = low priority (queue 1, 2)
0 - 3 = normal priority (queue 3, 4)
4 - 5 = medium priority (queue 5, 6)
6 - 7 = high priority (queue 7, 8)
If No-override (the default) is configured for the 802.1p priority
associated with a codepoint, the priority in the packet header
is not re-marked by the global IP-Diffserv classifier and, by
default, is sent to the “normal priority” outbound port queue.
IP Packet Sent Out
a Tagged Port in a
VLAN
Based on the IP Precedence bit set in
a packet’s ToS/Traffic Class field:
• The packet is sent to one of eight
outbound port queues in the
switch as described above.
Based on the DSCP codepoint that the switch has been config-
ured to detect, one of the following actions is taken:
• The codepoint is re-marked according to the configured
DSCP policy and the 802.1p priority currently configured for
the codepoint in the DSCP Policy Table (Table 6-8).
• The IP Precedence value (0 - 7) is
used to set the corresponding
802.1p priority in the VLAN tag
carried by the packet to the next
downstream device (see Table 6-
8).
• The codepoint is not changed, but the 802.1p priority is
marked with the currently configured value for the
codepoint in the DSCP Policy Table (Table 6-8).
Based on the new 802.1p priority marking, the packet leaves
the switch through one of the outbound port queues described
above.
In addition, the priority value (0 - 7) is used to set the 802.1p
priority in the VLAN tag carried by the packet to the next
downstream device. If the priority is configured as No-over-
ride in the DSCP Policy table, the VLAN tag carries a “0”
(normal priority) 802.1p setting if not prioritized by other global
QoS classifiers.
6-53