![qdisc handle
• Qdisc handle is used to identify Qdisc
- {none|major[:]}
- none is TC_H_UNSPEC
- major is 16bits HEX number(Without ‘0x’ prefix)
- : is optional
• Internally, qdisc_handle = major<<16](https://image.slidesharecdn.com/tcbasics-121014205427-phpapp02/85/Tc-basics-17-320.jpg)
![classid
• Classid is used to identify Class
- {none|root|[major]:minor}
- none is TC_H_UNSPEC, root is TC_H_ROOT
- major/minor are both 16bits HEX numbers(Without
‘0x’ prefix), major is optional
• Internally, classid = (major<<16)|minor](https://image.slidesharecdn.com/tcbasics-121014205427-phpapp02/85/Tc-basics-18-320.jpg)
![tbf
• limit/latency
• buffer/burst/maxburst, capcity of token
bucket: size[/cell]
• mpu: minimum process unit
• rate/peakrate
• Max(Rate/HZ,MTU)](https://image.slidesharecdn.com/tcbasics-121014205427-phpapp02/85/Tc-basics-32-320.jpg)
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Tc basics
- 1. Dive into TC – TC basics Jeromy Fu
- 2. Agenda • What’s TC • How it works • Basic concepts • Command and parameters
- 3. What’s TC • TC is abbr. of Traffic Control - Rate control - Bandwidth management - Active Queue Management(AQM) - Network Emulator, pkt loss, pkt disorder, pkt duplication, pkt delay - QoS ( diffserv + rsvp ) - Many more …
- 4. What’s tc • user-level utilities iproute2( iproute2/tc ) • tc kernel (linux/net/sched)
- 5. How it works
- 6. How it works
- 7. Basic concepts- Qdisc • Qdisc(Queue discipline) - Decide which ones to send first, which ones to delay, and which ones to drop - class/classful Qdisc: Qdisc with/without configurable internal subdivision • Naming convention: - Kernel: sch_*.c (sch_netem.c, sch_tbf.c ) - iproute2: q_*.c (q_netem.c, q_tbf.c)
- 8. Qdisc list • Class Based Queueing (CBQ) • Hierarchical Token Bucket (HTB) • Hierarchical Fair Service Curve (HFSC) • ATM Virtual Circuits (ATM) • Multi Band Priority Queueing (PRIO) • Hardware Multiqueue-aware Multi Band Queuing (MULTIQ) • Random Early Detection (RED) • Stochastic Fairness Queueing (SFQ) • True Link Equalizer (TEQL) • Token Bucket Filter (TBF) • Generic Random Early Detection (GRED) • Differentiated Services marker (DSMARK) • Network emulator (NETEM) • Deficit Round Robin scheduler (DRR) • Ingress Qdisc
- 9. Basic concepts- Classification • Classification(Filter) - Used to distinguish among different classes of packets and process each class in a specific way. • Naming convention: - Kernel: cls_*.c (cls_u32.c, cls_rsvp.c ) - iproute2: f_*.c (f_u32.c, f_rsvp.c)
- 10. Classification list • Elementary classification (BASIC) • Traffic-Control Index (TCINDEX) • Routing decision (ROUTE) • Netfilter mark (FW) • Universal 32bit comparisons w/ hashing (U32) • IPv4 Resource Reservation Protocol (RSVP) • IPv6 Resource Reservation Protocol (RSVP6) • Flow classifier • Control Group Classifier • Extended Matches • Metadata • Incoming device classification
- 11. Basic concepts- Action • Action Actions get attached to classifiers and are invoked after a successful classification. They are used to overwrite the classification result, instantly drop or redirect packets, etc. Works on ingress only. • Naming convention: - Kernel: act_*.c (act_police.c, act_skbedit.c ) - iproute2: m_*.c (m_police.c, m_pedit.c)
- 12. Action list • Traffic Policing • Generic actions • Probability support • Redirecting and Mirroring • IPtables targets • Stateless NAT • Packet Editing • SKB Editing
- 13. Basic concepts- Class • Classes either contain other Classes, or a Qdisc is attached • Qdiscs and Classes are intimately tied together
- 14. TC Commands • OPTIONS: options are effective for all sub commands • OBJECTS: the object of the tc command operates on • COMMAND: the sub command for each object
- 15. TC Commands
- 16. TC Qdisc • Operations on qdisc: add | del | replace | change | show • Handle: qdisc handle used to identify qdisc • root|ingress|parent CLASSID, specify the parent node
- 17. qdisc handle • Qdisc handle is used to identify Qdisc - {none|major[:]} - none is TC_H_UNSPEC - major is 16bits HEX number(Without ‘0x’ prefix) - : is optional • Internally, qdisc_handle = major<<16
- 18. classid • Classid is used to identify Class - {none|root|[major]:minor} - none is TC_H_UNSPEC, root is TC_H_ROOT - major/minor are both 16bits HEX numbers(Without ‘0x’ prefix), major is optional • Internally, classid = (major<<16)|minor
- 19. stab and rtab • stab is Size table, rtab is rate table. • They’re used to speed up the calculation of the transmit time of packets. • The packet size is aligned to a predefined size in the stab slot. • Then the rtab is used to give the pre- calculated time of the aligned packet size.
- 20. Linklayer • Link layer affects packet size, if linklayer is set, both mpu and overhead must also be set
- 21. Linklayer
- 22. stab internal • szopts: stab relating specifications, some are specified by the command, some are calculated • data: the size table.
- 23. stab internal - user space • Averagely distribute(*2) the MTU size into size table which has tsize slots
- 24. stab internal - kernel
- 25. rtab internal - user space • rtab size is constantly 256
- 26. rtab internal - kernel
- 30. TC Class • Tc class can only be applied for classful qdisc, such as htb, cbq etc
- 32. tbf • limit/latency • buffer/burst/maxburst, capcity of token bucket: size[/cell] • mpu: minimum process unit • rate/peakrate • Max(Rate/HZ,MTU)
- 33. tbf - user space • latency convert to limit finally
- 34. tbf - user space • rtab initialization
- 35. tbf - kernel
- 36. tbf - kernel
- 37. Tbf dequeue