Egress%20traffic%20shaping%20on%20Linux%20using%20Hierarchical%20Token%20Bucket%20(HTB)

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Egress traffic shaping on Linux using
Hierarchical Token Bucket (HTB)

• Brad Baker
• CS522
• 12.10.2003

2
Traffic Shaping Overview

• Manages limited network resources
• Has many applications where desired network use
  exceeds available resources
• Can provide control, efficiency, and guaranteed
  quality of service, QoS
• Limits contention for resources
• Most useful on outbound (Egress) streams, some
  options for Ingress.

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Traffic Control

• Feature included in current Linux distributions
• Includes classless and classful queuing
  disciplines
• Need TC function to be bottleneck, not external
  router or other device
• Several classless techniques available
• FIFO, SFQ, TBF
• Several classful techniques available
• HTB, CBQ, PRIO

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HTB Hierarchical Token Bucket

• Classful queuing discipline
• Similar to Class Based Queuing (CBQ)
• Hierarchy of classes combined with filters are
  used to control traffic
• System periodically produces tokens, needed to
  send frames over the interface
• Classes send data if tokens are available
• If no tokens, can borrow from parent

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HTB classes

• Root classes cannot borrow from one another
• Traffic can only be classified to leaf classes
• Inner classes allow borrowing to children
• Egress packets are classified and placed in
  correct subclass
• Dequeue request given to root, proceeds down tree
  until it can be fulfilled

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HTB specifics

• Bucket based storage of tokens accommodates burst
  traffic, such as web
• Same concept in classless discipline TBF
• Can use same feature to smooth bursts
• Good for situations with fixed bandwidth to
  distribute among competitors
• Can provide guaranteed min service rate, and
  constrain to max bandwidth use to ceiling rate
• Supports priority values associated with classes
• More efficient and fewer parameters than CBQ

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Some HTB results
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HTB syntax

• tc qdisc del dev eth0 root
• tc qdisc add dev eth0 root handle 2 htb default
  1
• tc class add dev eth0 parent 2 classid 21 htb
  rate 100kbps ceil 100kbps prio 0
• tc qdisc add dev eth0 parent 21 handle 1 htb
  default 1
• tc class add dev eth0 parent 1 classid 11 htb
  rate 70kbps ceil 70kbps prio 0
• tc class add dev eth0 parent 11 classid 110 htb
  rate 35kbps ceil 70kbps prio 1 burst 10k
• tc class add dev eth0 parent 11 classid 111 htb
  rate 35kbps ceil 70kbps prio 1 burst 10k
• tc qdisc add dev eth0 parent 110 handle 10 sfq
  perturb 10
• tc qdisc add dev eth0 parent 111 handle 11 sfq
  perturb 10
• tc class add dev eth0 parent 1 classid 12 htb
  rate 30kbps ceil 30kbps prio 0
• tc class add dev eth0 parent 12 classid 120 htb
  rate 15kbps ceil 30kbps prio 1 burst 10k
• tc class add dev eth0 parent 12 classid 121 htb
  rate 15kbps ceil 30kbps prio 1 burst 10k
• tc class add dev eth0 parent 1 classid 13 htb
  rate 100kbps ceil 100kbps prio 1 burst 10k

• Creates four qdiscs and eight classes
• One non-root qdisc used to enforce 100K
• Two non-root qdiscs used for SFQ

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HTB improvements

• Problem HTB divides predetermined bandwidth
  values between classes
• Works well in situations with fixed bandwidth
• Improvement Process could be enhanced by giving
  classes relative bandwidth values
• Find potential channel capacity and use as root
  bandwidth

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HTB improvements

• Problem Discrepancy between quantum value and
  actual packet size
• Can cause errors in cases of high bandwidth
  contention
• Improvement Calculate bandwidth based on actual
  dequequed bytes
• Instead of bytes specified by the model

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Conclusion

• Traffic shaping is useful and important
• When resources exceed demand
• When an interface changes from fast connection to
  slow connection
• HTB provides a well supported TC solution
• Efficient and accurate shaping traffic among
  predetermined bandwidth values
• Allows resource control comparable to high-end
  dedicated bandwidth management systems.
• Included in recent (2.4.20 or later) Linux
  kernels

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References

• Linux Advanced Routing Traffic Control HOWTO
  (LARTC)
• Author Bert Hubert and others
• http//lartc.org/howto/
• Traffic Shaping with Linux
• Author Shane Chen
• http//www.knowplace.org/shaper/index.html
• HTB Linux queuing discipline manual - user guide
• Author Martin Devera
• http//luxik.cdi.cz/devik/qos/htb/manual/userg.ht
  m
• Traffic Control HOWTO
• Author Martin A. Brown
• http//linux-ip.net/articles/Traffic-Control-HOWTO
  /index.html