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6-147
Configuring the Switch
Class of Service (CoS): Managing Bandwidth More Effectively
Configuring the Switch
Packet Enters Switch: On a Non-VLAN Port or in an Untagged VLAN
Packet Exits From Switch: On a Non-VLAN Port or in an Untagged VLAN
(Prioritizing affects only the choice of outbound priority queue. The packet carries no 802.1p priority tag.)
1. Device Priority (IP Address) Option
(IP Packets Only)
:
– If Device Priority does not apply to the packet, then packet priority defers to the ToS policy.
– If Device Priority (0 - 7) is configured and applies to a packet, the packet is assigned to the appropriate queue (high
or normal priority) of the outbound port, regardless of any other CoS-configured policy.
2. Type of Service (ToS) Option
(IP Packets Only)
:
– If ToS option is configured to Disabled, then packet priority defers to the Protocol Priority policy.
– IP Precedence option: Prioritizes packet (high or normal) according to the value of the ToS precedence bits (upper
three bits of ToS field; 0 - 7); 4 - 7 = high, 0 - 3 = normal.
– Differentiated Services option
: Prioritizes packet (high or normal) according to Priority setting (0 - 7) for packet’s
ToS field codepoint. If Priority is set to No override (the default), then packet priority defers to the Protocol Priority
policy.
See “Using Type of Service (ToS) Criteria to Prioritize IP Traffic” on 6-143.
3. Protocol Priority Option
:
– If Protocol Priority does not assign a priority to the packet, then packet priority defers to the VLAN ID policy.
– If Protocol Priority assigns a priority (0 - 7) to a packet, the packet is assigned to the appropriate queue (high or
normal priority) of the outbound port.
4. VLAN Priority Option
:
– If VLAN Priority does not assign a priority to the packet, then the packet goes to the “normal” priority queue of an
outbound port.
– If VLAN Priority assigns a priority (0 - 7) to a packet, the packet is assigned to the appropriate queue (high or normal
priority) of the outbound port.
(An outbound packet belonging to an untagged VLAN can be assigned to a high or normal priority queue, but cannot
be assigned an 802.1p priority because there is no tagged VLAN field in the packet.)