Quality of Service
CLASSIFICATION AND MARKING
What is QoS?
1.
It’s a CCIE topic – but that doesn’t mean you can’t learn!
1.
Understand traffic flows
A
TCP
SYN
SYN, ACK
ACK
ESTABLISHED
B
A
UDP
B
SRC & DST IPs and Ports
Categories of QoS
1.
Classification and Marking
Packet
2.
(EF)Packet
Congestion Management and Avoidance
(AF21)Data Packet
(EF)Voice Packet
Hardware
Queue
Categories of QoS
1.
Classification and Marking
Packet
2.
(EF)Packet
Congestion Management and Avoidance
(AF21)Data Packet
Soft Priority Queue
Hardware
Queue
(EF)Voice Packet
3.
Soft Queue
Shaping, Policing, and Link Fragmentation
1.
Rate limiting
1.
Shaping buffers offending packets while policing is a little more rough and by default drops offending packets.
QoS Fields
1.
IP ToS Byte
2.
CoS (802.1q and ISL)
3.
WAN
QoS Fields
1.
IP ToS Byte
QoS Fields
1.
CoS and WAN fields
1.
2.
CoS has 3 bits to work with on the 802.1q header and ISL header
WAN markings aren’t’ much
1.
MPLS has 3 bits to work with, Frame-Relay and ATM both have 1 bit
1.
IP header maintains it’s markings, but not much good over L2 and L2.5 WAN networks
QoS Fields Continued…
Field
Location
Length
IP Precedence (IPP)
IP Header
3 bits
IP DSCP
IP Header
6 bits
DS Field
IP Header
1 byte
ToS Byte
IP Header
1 byte
CoS
ISL and 802.1q header
3 bits
Discard Eligible (DE)
Frame Relay header
1 bit
Cell Loss Priority (CLP)
ATM cell header
1 bit
MPLS Experimental
MPLS header
3 bits
Per Hop Behaviors (PHB)
DSCP Class Selector
Names
Binary DSCP Values
IPP Binary Values
IPP Names
Default/CS0*
000000
000
Routine
CS1
001000
001
Priority
CS2
010000
010
Immediate
CS3
011000
011
Flash
CS4
100000
100
Flash Override
CS5
101000
101
Critical
CS6
110000
110
Internetwork Control
CS7
111000
111
Network Control
Assured Forwarding PHB and DSCP Values
Queue
Class
Low Drop Probability
Medium Drop Probability
High Drop Probability
Name/Decimal/Binary
Name/Decimal/Binary
Name/Decimal/Binary
1
AF11 / 10 / 001010
AF12 / 12 / 001100
AF13 / 14 / 001110
2
AF21 / 18 / 010010
AF22 / 20 / 010100
AF23 / 22 / 010110
3
AF31 / 26 / 011010
AF32 / 28 / 011100
AF33 / 30 / 011110
4
AF41 / 34 / 100010
AF42 / 36 / 100100
AF43 / 38 / 100110
Expedited Forwarding PHB and DSCP Values
1. Two PHBs
1. Quick scheduling low latency queuing
2. Police to ensure EF packets do not hog all the bandwidth and/or starve
the other queues.
3. Decimal 46 – Binary 101110
Assured Forwarding PHB and DSCP
Values Continued…
1.
AF11 / 10 / 001010
1.
AF1 | 1 = 001 | 01 | 0
1.
2.
001010 = 10
AF43 / 38 / 100110
1.
AF4 | 3 = 100 | 11 | 0
1.
100110 = 38
Modular Quality of Service CLI
1.
Class map
1.
2.
Policy Map
1.
3.
Used to Classify your traffic
Used to Mark your traffic (and choose what to do with marked traffic) this is also where you set
Congestion Management and Policing. Normally we want to keep marking as close to the source as
possible, but best practices aren’t always possible…
Service Policy
1.
Same thing as a policy-map, but you use the service-policy command on an interface to apply the
policy map
Network Based Application Recognition
(NBAR)
1.
NBAR is also known as Deep Packet Inspection
2.
NBAR has the ability to look past TCP and UDP ports such as the URL, MIME type in HTTP
requests allowing recognition of application information
3.
Ability to use regular expressions to isolate the domain or another portion
4.
Use the match protocol command under a class map to use NBAR to match traffic