QoS - Classification and Marking
9 important questions on QoS - Classification and Marking
Which 7 traffic descriptors are typically used for classification?
2. Layer 1 (Physical interface, subinterface, port)
3. Layer 2 (MAC address and 802.1Q/p Class of Service bits.
4. Layer 2.5 (MPLS Experimental (EXP) bits)
5. Layer 3 (Differentiated Service Code Points DSCP, IP Precedence IPP, and source/destination IP address
6. Layer 4 (TCP or UDP Ports)
7. Layer 7 (Next Generation Network-Based Application Recognition (NBAR2)
What is Next Generation Network-Bases Application Recognition, or NBAR2?
It can recognize more than 1000 application and gets monthly protocol packs for new or changed applications.
What are the 2 modes of operation of NBAR2?
Discovers and gets real-time statistics from application running on the network, which then can be used in defining QoS classes and policies using MQC configuration.
2. Modular QoS CLI (MQC)
Using MQC network traffic that matches specific network protocols can be assigned to a traffic class.
After which different QoS policies can be assigned per traffic class.
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Which Traffic Descriptors are used for Traffic Marking?
2. Layer 2 (802.1Q/p)
3 Layer 2.5 (MPLS EXP bits)
4 Layer 3 (DCSP and IPP)
Layer 2 and Layer 3 are the Traffic Descriptors used most often in Enterprise Networks.
What is the PCP or Priority Code Point field and what is it used for?
It is used to mark packets as belonging to a specific CoS (Class of Service) and can use 8 different priority levels.
Level 0 is the lowest for background traffic and level 7 is the highest for Network Control
What is a drawback of using the PCP CoS markings?
This can be overcome by mapping CoS markings to another marking.
For example CoS priority levels correspond directly to IPv4 IP Precedence ToS values so they can be mapped directly to each other.
What are the 2 options to mark Layer 3 packets?
2. Differentiated Services Field, which is the same 8-bit field as the ToS field, however it has been redefined by newer standards.
Backwards compatible with ToS
It is composed of a 6 bit Differentiated Service Code Point (DSCP) fiels that allows classification of up to 64 classes. And a 2 bit Explicit Congestion Notification (ECN) field.
What is a DiffServ Behaviour Aggregate?
Routers can make Per-Hop Behaviour (PHB) decisions, which are based on DiffServ BAs
Which 4 PHBs have been defined and characterized for general use?
2. Default Forwarding PHB: Used for best effort service
3. Assured Forwarding PHB: Used for guaranteed bandwidth service.
4. Expedited Forwarding PHB: Used for low-delay service
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