1. Queuing Mechanisms

2. Objectives Upon completing this module, you will be able to:
Describe and configure FIFO queuing
Describe and configure priority queuing (PQ)
Describe and configure custom queuing (CQ)
Describe and configure basic weighted fair queuing (WFQ), distributed WFQ, ToS-based distributed WFQ, and QoS-group-based distributed WFQ
Describe and configure modified deficit round robin (MDRR) queuing
Describe and configure IP RTP Prioritization
Lesson Aim
<Enter lesson aim here.>
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3. Queuing Overview

4. Objectives Upon completing this lesson, you will be able to:
Understand how queuing works on Cisco routers
List the most used queuing mechanisms
Lesson Aim
<Enter lesson aim here.>
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5. Queuing in Cisco IOS
Cisco routers running Cisco IOS have a number of different queuing mechanisms
This module focuses on the following:
First In First Out (FIFO)
Priority Queuing (PQ)
Custom Queuing (CQ)
Weighted Fair Queuing (WFQ) with the different distributed versions
Modified Deficit Round Robin (MDRR)
IP RTP Prioritization
These mechnisms are implemented as software queues
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6. Output Interface Queue Structure
Forwarder
Software
Queuing
System
Hardware
Queue
(TxQ)
Output
Interface
Always FIFO
Any supported queuing mechanism
Each interface has its hardware and software queuing system.
The hardware queuing system (transmit queue, or TxQ) always uses FIFO queuing.
The software queuing system can be selected and configured depending on the platform and Cisco IOS version.
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7. Bypassing the Software Queue
Empty?
Hardware Queue
Full?
Hardware
Queue
(TxQ)
Yes No No
Yes
Software
Queuing
System
When a packet is being forwarded, the router will bypass the software queue if:
The software queue is empty, and
The hardware queue is not full
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8. Hardware Queue (TxQ) Size
Routers determine the length of the hardware queue based on the configured bandwidth of the interface.
Long TxQ may result in poor performance of the software queue.
Short TxQ may result in a large number of interrupts which causes high CPU use and low link use.
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9. Software Queuing System
Queuing Components
Forwarded Packets
Software Queuing System
Class 1?
Add/Drop
Queue 1
Hardware
Queuing System
Class 2?
Interface
Add/Drop
Queue 2
Scheduler
Hardware Q
Class n?
Add/Drop
Queue n
Each queuing mechanism has three main components that define it:
Classification (selecting the class)
Insertion policy (determining whether a packet can be enqueued)
Service policy (scheduling packets to be put into the hardware queue)
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10. Summary Upon completing this lesson, you should be able to:
Understand how queuing works on Cisco routers
List the most used queuing mechanisms
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11. Lesson Review Which queuing mechanisms do Cisco routers support?
When are software queuing mechanisms not used?
How does TxQ length affect the software queuing system?
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12. FIFO Queuing

13. Objectives Upon completing this lesson, you will be able to:
Describe FIFO queuing
Describe the drawbacks of FIFO queuing
Configure FIFO queuing on Cisco routers
Monitor and troubleshoot FIFO queuing
Lesson Aim
<Enter lesson aim here.>
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14. FIFO Queuing
Forwarded Packets
FIFO Queuing System
Hardware
Queuing System
Interface
FIFO
Scheduler
All in one
queue
Tail-drop
Queue 1
Hardware Q
Newly arriving packets are dropped if the queue is full.
FIFO uses one single queue.
All packets are classified into one class.
Routers serve packets in the first-come, first-serve fashion.
The software FIFO queue is basically an extension of the hardware FIFO queue.
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15. Benefits and Drawbacks of FIFO Queuing
Simple and fast (one single queue with a simple scheduling mechanism)
Supported on all platforms
Supported in all switching paths
Supported in all IOS versions
Drawbacks
Unfair allocation of bandwidth among multiple flows
Causes starvation (aggressive flows can monopolize links)
Causes jitter (bursts or packet trains temporarily fill the queue)
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16. Configuring FIFO Queuing
Router(config-if)#
no fair-queue
FIFO queuing is enabled by default on all interfaces. that have a default bandwidth of more than 2 Mbps
Weighted fair queuing is enabled if the bandwidth is less than 2 Mbps.
Disable WFQ to enable FIFO on interfaces that have less than 2 Mbps of bandwidth.
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17. Configuring FIFO Queuing (cont.)
Router(config-if)#
hold-queue <buffers> out
FIFO queuing allows a maximum of 40 packets to be stored in the output queue.
This command can be used to increase or decrease the maximum number of buffered packets.
A large value can be set to support longer bursts (fewer drops, more buffer usage).
A small value can be set to prevent bursts (more drops).
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18. FIFO Example interface Ethernet0/0 ip address 1.1.1.1 255.0.0.0 !
The Ethernet interface has a default bandwidth of 10Mbps.
FIFO is the default queuing mechanism, and it does not need to be configured.
interface Ethernet0/0
ip address !
interface Serial0/0
ip address
no fair-queue
hold-queue 50 out
The serial interface (A/S) has a default bandwidth of 128 kbps.
WFQ is the default queuing mechanism, and it has to be disabled to enable FIFO queuing.
Up to 50 frames are allowed to be enqueued before the router will start tail-dropping newly arriving packets.
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19. Monitoring and Troubleshooting FIFO
Router#
show interface [<interface>]
The command displays information about the selected interface(s).
Router#show interface Serial0/0 Serial0/0 is up, line protocol is up
Hardware is PowerQUICC Serial
Internet address is /8
MTU 1500 bytes, BW 128 Kbit, DLY usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:00:02, output 00:00:04, output hang never
Last clearing of "show interface" counters never
Queueing strategy: fifo
Output queue 0/50, 0 drops; input queue 0/75, 0 drops
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec …
The queue is currently empty (0/50).
There can be a maximum of 50 frames in the queue (0/50).
FIFO queuing is enabled on an interface with a default bandwidth of 128kbps.
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20. Summary Upon completing this lesson, you should be able to:
Describe FIFO queuing
Describe the drawbacks of FIFO queuing
Configure FIFO queuing on Cisco routers
Monitor and troubleshoot FIFO queuing
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21. Lesson Review Why is FIFO the fastest queuing mechanism?
Describe the classification and scheduling of FIFO queuing.
List the drawbacks of FIFO queuing.
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22. Priority Queuing

23. Objectives Upon completing this lesson, you will be able to:
Describe priority queuing
Describe the benefits and drawbacks of priority queuing
Configure priority queuing on Cisco routers
Monitor and troubleshoot priority queuing
Lesson Aim
<Enter lesson aim here.>
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24. Priority Queuing System
Forwarded Packets
Priority Queuing System
High?
Tail-drop
Queue 1
Hardware
Queuing System
Medium?
Tail-drop
Queue 2
Pre-emptive
Scheduler
Interface
Hardware Q
Normal?
Tail-drop
Queue 3
Low?
Tail-drop
Queue 4
Priority queuing (PQ) uses four FIFO queues.
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25. Priority Queuing Classification
Priority queuing classification for IP supports these options:
Source interface
IP access list (standard and extended)
Packet size (greater or smaller than specified)
Fragments
TCP source or destination port numbers
UDP source or destination port numbers
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26. Priority Queuing Classification (cont.)
Priority queuing also supports classification of other protocols with these options:
Protocol-specific access list (if available for the specified protocol)
Packet size (greater or smaller than specified)
Some of the supported protocols are:
IPX
CLNS
DECnet
AppleTalk
VINES
DLSw
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27. Priority Queuing Insertion Policy
Each queue has a maximum number of packets that it can hold (queue size).
After a packet is classified to one of the following queues, the router will enqueue the packet if the queue limit has not been reached (tail-drop within each class).
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28. Scheduling Priority Queuing
Packet in
HIGH
queue? No
Packet in
MEDIUM
queue?
Yes No
Packet in
NORMAL
queue?
Yes No
Packet in
LOW
queue?
Yes No
Yes
Dispatch packet
and start checking the
HIGH queue again
Hardware Q
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29. Benefits and Drawbacks of Priority Queuing
Provides low-delay propagation to high-priority packets
Supported on most platforms
Supported in all IOS versions (above 10.0)
Drawbacks
All drawbacks of FIFO queuing within a single class
Starvation of lower-priority classes when higher-priority classes are congested
Manual configuration of classification on every hop
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30. Configuring Priority Queuing
Configure priority lists
Configure classification
Select a queue
Set maximum queue size
Apply the priority list to outbound traffic on an interface
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31. Priority Queuing Classification
Router(config)#
priority-list list-number protocol protocol-name {high|medium|normal|low} queue-keyword keyword-value
Selects the queue based on Layer-3 protocol
Additional classification (queue-keyword):
fragment (IP packets with non-zero fragment offset)
gt/lt <size>: based on packet size (including L2 frame)
list <acl>: ACL classification
tcp/udp <port>: TCP or UDP port number
System and link-level messages are classified in queue high by default
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32. Priority Queuing Classification (cont.)
Router(config)#
priority-list list-number interface intf {high|medium|normal|low}
Classifies the packet based on incoming interface
Router(config)#
priority-list list-number default {high|medium|normal|low}
Classifies all unclassified packets in a default queue
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33. Priority Queuing Scheduling and Dropping Parameters
Router(config)#
priority-list list-number queue-limit high medium normal low
Specifies the maximum queue size of individual priority queues
Assigns priority queuing definition to an interface
Router(config-if)#
priority-group list
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34. Sample PQ Configuration
WAN Core
Core E1
interface serial0
priority-group 1
priority-list 1 protocol ip high list 101
priority-list 1 interface ethernet 0 medium
priority-list 1 default normal
priority-list 1 queue-limit
access-list 101 permit tcp any any eq 23
Branch
Office
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35. Monitoring Priority Queuing
Router#
show interface interface
Displays information and statistics about queuing on interface
Router#
show queueing [priority|custom|fair|random-detect] interface
Displays queuing parameters on interface
Router#
show queue interface
Displays queue contents
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36. show interface Router#show interface serial 1/0
Serial1/0 is up, line protocol is up
Hardware is M4T
Internet address is /8
MTU 1500 bytes, BW 19 Kbit, DLY usec, rely 255/255, load 93/255
Encapsulation HDLC, crc 16, loopback not set
Keepalive set (10 sec)
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0 (size/max/drops); Total output drops: 0
Queueing strategy: priority-list 1
Output queue (queue priority: size/max/drops):
high: 0/20/0, medium: 0/40/0, normal: 0/60/0, low: 0/80/0
5 minute input rate bits/sec, 8 packets/sec
5 minute output rate 7000 bits/sec, 8 packets/sec
… rest ignored ...
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37. show queueing priority
Router#show queueing priority
Current priority queue configuration:
List Queue Args
high protocol ip list 101
medium interface Ethernet6/0
The show queueing priority command displays only the nondefault parameters.
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38. Summary Upon completing this lesson, you should be able to:
Describe priority queuing
Describe the benefits and drawbacks of priority queuing
Configure priority queuing on Cisco routers
Monitor and troubleshoot priority queuing
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39. Lesson Review When would you use priority queuing?
What are the benefits and drawbacks of priority queuing?
How many classes does priority queuing support?
How does priority queuing schedule packets?
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40. Weighted Fair Queuing

41. Objectives Upon completing of this lesson, you will be able to:
Describe WFQ
Describe the benefits and drawbacks of WFQ
Configure WFQ on Cisco routers
Monitor and troubleshoot WFQ
Lesson Aim
<Enter lesson aim here.>
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42. Weighted Fair Queuing
Queuing algorithm should fairly share the bandwidth among flows by:
Reducing response time for interactive flows by scheduling them to the front of the queue
Preventing high volume conversations from monopolizing an interface
Implementation: Messages are sorted into conversations (flows) and transmitted by the order of the last bit crossing the flow channel.
Unfairness is reinstated by introducing “weight” (IP Precedence) to give proportionately more bandwidth to flows with higher weight.
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43. Weighted Fair Queuing (cont.)
Forwarded Packets
Weighted Fair Queuing System
Flow 1?
WFQ drop
Queue 1
Hardware
Queuing System
Flow 2?
WFQ drop
Queue 2
WFQ
Scheduler
Interface
Hardware Q
Flow N?
WFQ drop
Queue N
WFQ uses per-flow FIFO queues.
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44. Weighted Fair Queuing Implementations
Implementation parameters:
Queuing platform: central CPU or VIP
Classification mechanism
Weighted fairness
Modified tail drop within each queue
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45. WFQ Classification Packets of the same flow end up in the same queue.
IP TCP Payload
WFQ classification uses these parameters:
Source IP address
Destination IP address
Source TCP or UDP port
Destination TCP or UDP port
Transport protocol
Type of service (ToS) field
Src.
Addr.
Dest.
Addr.
Protocol
ToS
Src.
Port
Dest.
Port
Hash Algorithm
A hash algorithm is used to produce the index of the queue where the packet is enqueued.
#queue (index of the queue)
Packets of the same flow end up in the same queue.
The ToS field is the only parameter that might change, causing packets of the same flow to end up in different queues.
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46. WFQ Classification Details
A fixed number of per-flow queues is configured.
A hash function is used to translate flow parameters into queue number.
System packets (eight queues) and RSVP flows (if configured) are mapped into separate queues.
Two or more flows could map into the same queue, resulting in lower per-flow bandwidth.
Important: The number of queues configured has to be larger than the expected number of flows.
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47. WFQ Insertion and Drop Policy
WFQ has two modes of dropping:
Early dropping when the congestive discard threshold (CDT) is reached
Aggressive dropping when the hold-queue out limit (HQO) is reached
WFQ always drops packets of the most aggressive flow.
Congestive Discard Policy as of 11.2(9)
cfilsfil>What is the exact criterium for the congestive discard policy?
agt> We keep track of the queue with the latest "delivery time" - in the example above, Fred called this (probably more accurately "from the deep sub-queue."). If the aggregate is about to be exceeded, we should either drop the new packet, or an existing. If the new one is for an already active queue, and has a "delivery time" later than the last packet on the deepest queue - the new one is dropped. If the deep queue time is later, we enqueue the new packet, and tail-drop from the deepest one.
But - I caution you against getting too detailed in how you interpret and test for this. We have refined (some would say corrected :-) :-) this behaviour over the years.
- each queue gets 1/4 of limit
- each queue gets whole limit
- each queue gets whole limit but aggregate applies
- ditto, but drop from deep sub-queue
- ditto, but always allow at least one (i.e. special case for non-active queue)
- and I'm sure there'll be more.
So unless it's really crucial in some particular circumstance, try to verify if you are really dependent on this level of detail. If you can observe undesirable behaviour for the network, or for the end-systems/hosts - let us know (even if WFQ is doing what it's designed to do :-) And beware testing other than on recent versions - where you might see the interim behaviours listed above (or others I have forgotten).
Implication
When the queue has congestive-discard-threshold (default: 64) messages in it, new messages are not enqueued for the conversations whose weighted depth is greatest. Lower bandwidth conversations (which include control message conversations) still enqueue data. A consequence of this is that the Fair Queue may occasionally have more messages in it than its theoretical maximum.
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48. WFQ Insertion and Drop Policy (cont.)
N>HQO?
N>CDT? No No
Enqueue
Packet
Nth Packet
Yes
Yes
Worst
Finish
Time?
Worst
Finish
Time?
Yes No No
Yes
Old
Drop the packet with the worst finish time (old) and enqueue the Nth packet (new).
Congestive Discard Policy as of 11.2(9)
cfilsfil>What is the exact criterium for the congestive discard policy?
agt> We keep track of the queue with the latest "delivery time" - in the example above, Fred called this (probably more accurately "from the deep sub-queue."). If the aggregate is about to be exceeded, we should either drop the new packet, or an existing. If the new one is for an already active queue, and has a "delivery time" later than the last packet on the deepest queue - the new one is dropped. If the deep queue time is later, we enqueue the new packet, and tail-drop from the deepest one.
But - I caution you against getting too detailed in how you interpret and test for this. We have refined (some would say corrected :-) :-) this behaviour over the years.
- each queue gets 1/4 of limit
- each queue gets whole limit
- each queue gets whole limit but aggregate applies
- ditto, but drop from deep sub-queue
- ditto, but always allow at least one (i.e. special case for non-active queue)
- and I'm sure there'll be more.
So unless it's really crucial in some particular circumstance, try to verify if you are really dependent on this level of detail. If you can observe undesirable behaviour for the network, or for the end-systems/hosts - let us know (even if WFQ is doing what it's designed to do :-) And beware testing other than on recent versions - where you might see the interim behaviours listed above (or others I have forgotten).
Implication
When the queue has congestive-discard-threshold (default: 64) messages in it, new messages are not enqueued for the conversations whose weighted depth is greatest. Lower bandwidth conversations (which include control message conversations) still enqueue data. A consequence of this is that the Fair Queue may occasionally have more messages in it than its theoretical maximum.
New
HQO (hold-queue out limit) is the maximum. number of packets that the WFQ system can hold.
CDT (congestive discard threshold) is the threshold when WFQ starts dropping packets of the most aggressive flow.
N is the number of packets in the WFQ system when the Nth packet arrives.
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49. Case Study
The WFQ system can hold a maximum of ten packets (hold-queue limit).
Early dropping (of aggressive flows) should start when there are eight packets (congestive discard threshold) in the WFQ system.
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50. Case Study: Interface Congestion
Absolute maximum (HQO=10) exceeded; new packet is the last in the TDM system and is dropped
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51. Case Study: Interface Congestion
Absolute maximum exceeded (HQO=10); new packet is not the last in the TDM system, so last packet is dropped
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52. Case Study: Flow Congestion
CDT exceeded (CDT=8); new packet would be the last in the TDM system and is dropped
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53. Case Study: Flow Congestion
CDT exceeded (CDT=8); new packet would not be the last, and packet is enqueued
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54. Drop Mechanism Within WFQ: Exception
Exception: A packet classified into an empty subqueue is never dropped.
The packet precedence has no effect on the dropping scheme.
Congestive Discard Policy as of 11.2(9)
cfilsfil>What is the exact criterium for the congestive discard policy?
agt> We keep track of the queue with the latest "delivery time" - in the example above, Fred called this (probably more accurately "from the deep sub-queue."). If the aggregate is about to be exceeded, we should either drop the new packet, or an existing. If the new one is for an already active queue, and has a "delivery time" later than the last packet on the deepest queue - the new one is dropped. If the deep queue time is later, we enqueue the new packet, and tail-drop from the deepest one.
But - I caution you against getting too detailed in how you interpret and test for this. We have refined (some would say corrected :-) :-) this behaviour over the years.
- each queue gets 1/4 of limit
- each queue gets whole limit
- each queue gets whole limit but aggregate applies
- ditto, but drop from deep sub-queue
- ditto, but always allow at least one (i.e. special case for non-active queue)
- and I'm sure there'll be more.
So unless it's really crucial in some particular circumstance, try to verify if you are really dependent on this level of detail. If you can observe undesirable behaviour for the network, or for the end-systems/hosts - let us know (even if WFQ is doing what it's designed to do :-) And beware testing other than on recent versions - where you might see the interim behaviours listed above (or others I have forgotten).
Implication
When the queue has congestive-discard-threshold (default: 64) messages in it, new messages are not enqueued for the conversations whose weighted depth is greatest. Lower bandwidth conversations (which include control message conversations) still enqueue data. A consequence of this is that the Fair Queue may occasionally have more messages in it than its theoretical maximum.
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55. WFQ Scheduling
Each packet is tagged with its finish time in a virtual TDM system.
The scheduler selects the packets with the earliest finish time tag (thus, the packet that leaves the virtual TDM the earliest).
Reference: “On the Efficient Implementation of Fair Queuing," Keshav, Berkeley, 1994
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56. Fair Queuing Finish Time Calculation
If Flow F active, then FT(Pk+1) = FT(Pk) + Size(Pk+1) otherwise FT(P0) = Now + Size(P0)
FT(A1)=0+100
FT(B1)=50+300
A1[100]
B1[300]
FT(A2)=100+20
A2[20]
WFQ does NOT schedule packets based on their arrival time (as would do FIFO).
WFQ does the following:
Packet arrival:
1. classify packet in its conversation queue
2. tag the packet with its finish round number:
The Finish round number is computed based on the following parameters:
- latest finish round number of the packet’s conversation
- packet size
Scheduling task:
Each time the wire is available, WFQ dequeues the packet with lowest finish round number and sends it on the wire
FT(B2)=
FT(A3)=120+10
A3[10]
B2[300] T
100 70 60 50
Thus the resulting scheduling is: B2 B1 A3 A2 A1
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57. Weight in WFQ Scheduling
WFQ System (Real-Size Packets)
Flow with P=001 2 1
Flow with P=000 3 2 1
Precedence-1 packets appear half the real size.
Virtual Packet Size = Real Packet Size / (IP Precedence + 1)
WFQ System (Virtual-Size Packets)
Flow with P=001 4 3 2 1
Precedence-1 flow gets twice as much bandwidth as Precedence-0 flow.
Flow with P=000 3 2 1
Hardware FIFO Queue 3 3 2 2 1 1
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58. Weighted Fair Queuing Finish Time Calculation
The finish time is adjusted based on the IP precedence of the packet.
If Flow F Active, Then FT(Pk+1) = FT(Pk) + Size(Pk+1)/(IPPrec+1) Otherwise FT(P0) = Now + Size(P0)/(IPPrec+1)
IOS implementation scales the finish time to allow integer arithmetic.
WFQ does NOT schedule packets based on their arrival time (as would do FIFO).
WFQ does the following:
Packet arrival:
1. classify packet in its conversation queue
2. tag the packet with its finish round number:
The Finish round number is computed based on the following parameters:
- latest finish round number of the packet’s conversation
- packet size
Scheduling task:
Each time the wire is available, WFQ dequeues the packet with lowest finish round number and sends it on the wire
If Flow F active, then FT(Pk+1) = FT(Pk) + Size(Pk+1)*4096/(IPPrec+1) otherwise FT(P0) = Now + Size(P0)*4096/(IPPrec+1)
RSVP packets and high-priority internal packets (PAK-Priority) have special weights (4 and 128).
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59. IP Precedence to Weight Mapping
4096 1
2048 2
1365 3
1024 4
819 5
682 6
585 7
512
32 (virtual IP Precedence)
128 (PAK-Priority)
1024 (virtual IP Precedence)
4 (RSVP)
RSVP packets and high-priority internal packets (PAK-Priority) have special weights (4 and 128).
Lower weight makes packets appear smaller (preferred).
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60. Weighted Fair Queuing Voice and Data Integration
WAN link speed 128 kbps
Voice requirements 30 kbps
VoIP is Precedence 5 (counts as 6 data sessions)
1 VoIP session, 5 data sessions
Voice gets up to 6/(6+5)*128 = 69 kbps (enough)
1 VoIP session, 20 data sessions
Voice gets up to 6/(6+20)*128 = 29 kbps (problem)
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61. Benefits and Drawbacks of Weighted Fair Queuing
Simple configuration (classification does not have to be configured)
Guarantees throughput to all flows
Drops packets of most aggressive flows
Supported on most platforms
Supported in all IOS versions (above 11.0)
Drawbacks
All drawbacks of FIFO queuing within a single queue
Multiple flows can end up in one queue
Does not support the configuration of classification
Can not provide fixed bandwidth guarantees
Performance limitations due to complex classification and scheduling mechanisms
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62. Weighted Fair Queuing Configuration
Router(config-intf)#
fair-queue [cdt [dynamic-queues [reservable-queues]]]
Congestive discard threshold (CDT)
Number of messages allowed in the WFQ system before the router starts dropping new packets for the longest queue
Value can range from 1 to 4096 (default is 64)
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63. Weighted Fair Queuing Configuration (cont.)
Router(config-intf)#
fair-queue [cdt [dynamic-queues [reservable-queues]]]
dynamic-queues
Number of dynamic queues used for best-effort conversations (values are: 16, 32, 64, 128, 256, 512, 1024, 2048, and 4096–the default is 256)
reservable-queues
Number of reservable queues used for reserved conversations in the range 0 to 1000 (used for interfaces configured for features such as RSVP - the default is 0)
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64. Weighted Fair Queuing Additional Parameters
Router(config-if)#
hold-queue max-limit out
Specifies the maximum number of packets that can be in all output queues on the interface at any time
The default value for WFQ is 1000
Under special circumstances WFQ can consume a lot of buffers, which may require lowering this limit
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65. Fair Queuing Defaults Fair queuing is enabled by default on:
Physical interfaces whose bandwidth is less than or equal to Mbps
Interfaces configured for Multilink PPP
Fair queuing is disabled:
If you enable the autonomous or silicon switching engine mechanisms
For any sequenced encapsulation: X.25, SDLC, LAPB, reliable PPP
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66. Monitoring and Troubleshooting WFQ
Router#
show interface interface
Displays interface delays, including the activated queuing mechanism with the summary information
Router#
show queue interface
Displays detailed information about the WFQ system of the selected interface
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67. show interface Router#show interface serial 1/0 Hardware is M4T
Internet address is /8
MTU 1500 bytes, BW 19 Kbit, DLY usec, rely 255/255, load 147/255
Encapsulation HDLC, crc 16, loopback not set
Keepalive set (10 sec)
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0 (size/max/drops); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/4/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
5 minute input rate bits/sec, 8 packets/sec
5 minute output rate bits/sec, 9 packets/sec
… rest deleted ...
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68. show queue Router#show queue serial 1/0
Input queue: 0/75/0 (size/max/drops); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 2/1000/64/0 (size/max total/threshold/drops)
Conversations 2/4/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
(depth/weight/discards/tail drops/interleaves) 1/4096/0/0/0
Conversation 124, linktype: ip, length: 580
source: , destination: , id: 0x0166, ttl: 254,
TOS: 0 prot: 6, source port 23, destination port 11033
Conversation 127, linktype: ip, length: 585
source: destination: , id: 0x020D, ttl: 252,
TOS: 0 prot: 6, source port 23, destination port 11013
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69. Queuing Comparison Weighted Fair Queuing Priority Queuing
Custom Queuing
No queue lists
Low-volume traffic given priority
Conversation dispatching
Interactive traffic gets priority
Works well on speeds up to 2 Mbps
Enabled by default
4 queues
High-priority queue serviced first
Packet-by-packet dispatching
Critical traffic gets through
Designed for low-bandwidth links
Must configure
16 queues
Round-robin service
Threshold dispatching
Proportional allocation
of bandwidth
Designed for medium-speed links
Must configure
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70. Summary Upon completing this lesson, you should be able to:
Describe WFQ
Describe the benefits and drawbacks of WFQ
Configure WFQ on Cisco routers
Monitor and troubleshoot WFQ
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71. Lesson Review How does WFQ classify packets?
When does WFQ drop packets?
How does WFQ schedule packets?
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72. Module Summary Upon completing this module, you should be able to:
Describe and configure FIFO queuing
Describe and configure priority queuing (PQ)
Describe and configure custom queuing (CQ)
Describe and configure basic weighted fair queuing (WFQ), distributed WFQ, ToS-based distributed WFQ, and QoS-group-based distributed WFQ
Describe and configure modified deficit round robin (MDRR) queuing
Describe and configure IP RTP Prioritization
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73. © 2001, Cisco Systems, Inc.
Queuing Mechanisms-73