QoS Flashcards
3 Cisco QoS Implementation Model
■ Best effort: QoS is not enabled for this model. It is used for traffic that does not require any special treatment.
■ Integrated Services (IntServ): Applications signal the network to make a bandwidth reservation and to indicate that they require special QoS treatment. [RSVP]
■ Differentiated Services (DiffServ): The network identifies classes that require special QoS treatment.[DSCP]
traffic descriptors are typically used for classification:
■ Internal: QoS groups (locally significant to a router)
■ Layer 1: Physical interface, subinterface, or port
■ Layer 2: MAC address and 802.1Q/p Class of Service (CoS) bits
■ Layer 2.5: MPLS Experimental (EXP) bits
■ Layer 3: Differentiated Services Code Points (DSCP), IP Precedence (IPP), and source/ destination IP address
■ Layer 4: TCP or UDP ports
■ Layer 7: Next Generation Network-Based Application Recognition (NBAR2)
3 Cisco Method of Marking Packets
■ Layer 2: 802.1Q/p Class of Service (CoS) bits
■ Layer 2.5: MPLS Experimental (EXP) bits
■ Layer 3: Differentiated Services Code Points (DSCP) and IP Precedence (IPP)
are traffic-conditioning QoS mechanisms used to classify traffic and enforce other QoS mechanisms such as rate limiting.
Traffic Shaping and Policing
Drop or re-mark incoming or outgoing traffic that goes beyond a desired traffic rate.
Policer
Buffer and delay egress traffic rates that momentarily peak above the desired rate until the egress traffic rate drops below the defined traffic rate. If the egress traffic rate is below the desired rate, the traffic is sent immediately.
Shaper
is a QoS mechanism responsible for distinguishing between different
traffic streams. It uses traffic descriptors to categorize an IP packet within a specific class.
Packet classification
deep packet inspection engine that can classify and identify a wide variety
of protocols and applications using Layer 3 to Layer 7 data, including difficult-to-classify
applications that dynamically assign Transmission Control Protocol (TCP) or User Datagram
Protocol (UDP) port numbers
Next Generation Network-Based Application Recognition (NBAR2)
Layer 3 QOS Marking that uses 3-bit field in TOC to give priorities in IP Packet.
IP precedence
is a deep packet inspection engine that can classify and identify a wide variety of protocols and applications using Layer 3 to Layer 7 data
NBRA2
NBRA2 two modes of operations
- Protocol Discovery - discover and get real time stat
- Modular QoS CLI (MQC) - matching a specific network protocol
Qos Mechanism that colours a packet by changing a field within a packet or frame header with a traffic descriptor
Packet Marking
Four Per-Hop-Behaviors for general use
- Class Selector (CS) - first 3bits are used as CS bit. Backward compatible with IP Precedence
- Default Forwarding (DF) - for best-effort service
- Assured Forwarding (AF) - used for guaranteed bandwidth service.
- Expedited Forwarding (EF) - used for low-delay service
Cisco IOS and shapers are based on :
Token Bucket algorithms
The policed traffic rate, in bits per second (bps)
Committed Information Rate (CIR)
