provide customized treatment with minimal impact on network performance
Layer 2: Three COS bits (802.1P) 0-7, inside 802.1Q header. Only on trunk links.
Layer 2.5: Three MPLS Experimental bits
Layer 3: One byte TOS bits
IP Precedence (IPP) - only uses three bits
Best practice
0 - No Tag
1-4 - Priority Classes
5 - high priority (VoIP)
6-7 - Network Traffic
Diff. Service Code Point (DSCP) - uses six bits, backwards compatible with IPP only reads first 3 bits
major (class selector - higher is better) + minor marking (drop preference - lower is better), last bit is always zero
AF assured forwarding (AF Class Drop)
EF expedited forwarding, should never be dropped
Marked at point of trust and carries through network
Policing and Shaping
By default interface transmits at line speed:
Shaping allows you to set the speed of traffic and queue everything beyond.
Policing allows you to set the speed of traffic and drops everything beyond.
Congestion Management and Avoidance
Queuing (more traffic than have bandwidth for)
FIFO - default
Weighted Fair - low bandwidth priority over high bandwidth
Class Based - bandwidth guarantee by class
Priority - one class, first bandwidth
LLQ - combines all
Congestion Avoidance
Weighted Random Early Detection - class to not be drop
TCP windowing - global synchronisation
Creating a QoS Policy
Class Map: Identify
Policy Map: Treatment
Service Policy: Application where policy is applied
class-map NAME match-all(Default)/match-any
match access-group name ACL_NAME
match protocol (NBAR2)
match dscp VALUE
show class-map
policy-map NAME
class CLASS_MAP_NAME
bandwidth (kbps) | percent 1-100 | remaining
priority (will drop over limit)
set dscp VALUE
int gi0/0
service-policy in/out POLICY_NAME
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