Comparing global IP type-of-service classifiers

The next table shows the difference in how global IP-Precedence and IP-Diffserv classifiers are implemented in the switch.

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)

  • 4 - 5 = medium priority (queue 5, 6)

  • 6 - 7 = high priority (queue 7, 8)

Based on the DSCP codepoint that the switch has been configured 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.

  • 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.

Based on the new 802.1p priority marking, the packet leaves the switch through one of the following queues:

  • 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.

  • 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 IP precedence-to-802.1p priority mapping).

Based on the DSCP codepoint that the switch has been configured to detect, one of the following actions is taken: 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-override in the DSCP Policy table, the VLAN tag carries a "0" (normal priority) 802.1p setting if not prioritized by other global QoS classifiers.