QOS - Classification and Marking Flashcards
(56 cards)
What is Packet Classification?
A QoS mechanism responsible for distinguishing between different traffic streams.
What are 7 Traffic Descriptors 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: DSCP, IP Precedence (IPP), and source/ destination IP address * Layer 4: TCP or UDP ports * Layer 7: NBAR2
What is NBAR2?
A 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 TCP or UDP port numbers.
What are NBAR2 two modes of operation?
- Protocol Discovery mode * Modular QOS CLI (MQC)
What are 2 things about NBAR2 Protocol Discovery Mode?
- It enables NBAR2 to discover and get real-time statistics on applications currently running in the network * These statistics can be used to define QoS classes and policies using MQC configuration.
NBAR2 Modular QOS CLI (MQC)
Network traffic such as Cisco Webex placed into one traffic class, while YouTube traffic placed into another traffic class.
What happens after traffic has been classified by NBAR2 in MQC mode?
Different QoS policies can be applied to the different classes of traffic.
What is Packet Marking?
A QoS mechanism that changes a field within a packet or a frame header with a traffic descriptor so it is distinguished from other packets during the application of other QoS mechanisms (such as re-marking, policing, queuing, or congestion avoidance).
What are 4 descriptors used for Marking traffic?
- Internal: QoS groups * 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)
What is the descriptor Internal: QOS groups?
Used by the router to mark packets as they are received and processed internally within the router and are automatically removed when packets egress the router.
When would a router use QOS groups descriptor?
Used only in special cases in which traffic descriptors marked or received on an ingress interface would not be visible for packet classification on egress interfaces due to encapsulation or de-encapsulation.
What are the 2 fields inserted into an 802.1q header?
- Tag Protocol ID (TPID) * Tag Control Information (TCI)
How big are the 2 fields inserted into an 802.1q header?
Each of the 2 fields are 2 bytes.
In an ethernet frame where is the 802.1q header located?
Behind the Source MAC address field
What is the TPID value?
0x8100 which identifies it as an 802.1q tagged frame
What 3 fields make up the TCI ?
- Priority Code Point (PCP) * Drop Eligible Indicator (DEI) * VLAN ID
What are the sizes of each of the 3 fields that make up the TCI?
- PCP 3 bits * DEI 1 bit * VLAN ID 12 bits
Which of the 3 fields are used for layer 2 QOS?
PCP
How many levels of COS are in the PCP?
8 levels - 0 thru 7
What are the 8 COS levels?
- Level 0 - BK - Background * Level 1 - BE - Best Effort * Level 2 - EE - Excellent Effort * Level 3 - CA - Critical apps * Level 4 - Video * Level 5 - VO - Voice * Level 6 - IC - Internetwork Control * Level 7 - NC - Network Control
In COS levels 4 and 5 what is the specified latency?
- Level 4 - VI - less than 100 ms latency and jitter * Level 5 - VO - less than 10 ms latency and jitter
What is the one drawback to using COS markings?
Frames lose their CoS markings when traversing a non-802.1Q link or a Layer 3 network.
How is the COS drawback overcome?
- Use higher layer markings whenever possible * the CoS priority levels correspond directly to IPv4’ s IP Precedence Type of Service (ToS) values so they can be mapped directly to each other
What is the default value of the DEI field and what does it mean?
- Default value is 0 * It means the frame cannot be dropped
