QoS

Linux has a number of traffic classifiers and filters for it's Traffic Control (TC) command. I have been collecting links from various places so I could try to aggregate the information in one place. Here are some links. I will need to summarize at some point in time.

• net: sched: add clsact qdisc: (adds a generalization of the ingress qdisc as a qdisc holding only classifiers)
• net: qdisc: add op to run filters/actions before enqueueAdd a new ->preclassify() op to allow multiqueue queuing disciplines to call tc_classify() or perform other work before dev_pick_tx().
• Add tcindex to conntrack and add netfilter target/matches: support for setting/matching the skb->tc_index field from Xtables, as well as allowing it to be saved/restored using connection tracking
• Networking CAKE Is Ready For Tasting With Linux 4.19 (2018/07/15)

On the Flow-Tools email list, Craig Weinhold published a cheat sheet for how to treat IP Packet ToS (Type of Service) bits:

**** Pre-1998

The IPv4 ToS byte was part of the original 1981 definition of Internet Protocol 
in RFC 791, which specified a 3-bit precedence value and 3-bits of ToS attributes. 
In the tables below, "tos" values refer to the entire byte. 
In 1992, RFC 1349 added a fourth ToS attribute. 

  0x80  0x40  0x20  0x10  0x08  0x04  0x02  0x01
+-----+-----+-----+-----+-----+-----+-----+-----+
|     PRECEDENCE  |    TOS attributes     |  -  |
+-----+-----+-----+-----+-----+-----+-----+-----+

         PRECEDENCE                     TOS attributes

name            dec tos bin     name              dec tos bin
network           7 224 111     min-delay           8  16 1000
internet          6 192 110     max-throughput      4   8 0100
critical          5 160 101     max-reliability     2   4 0010
flash-override    4 128 100     min-monetary-cost   1   2 0001
flash             3  96 011     normal              0   0 0000
immediate         2  64 010
priority          1  32 001
routine           0   0 000


**** Post-1998 

RFC 2474 reworked the ToS as a 6-bit Differentiated Services Code Point (DSCP) 
and, soon after, RFC 3168 allocated the lowest two bits for 
Error Congestion Notification (ECN, 
an IP analogy of frame-relay FECN and ATM EFCI). 

  0x80  0x40  0x20  0x10  0x08  0x04  0x02  0x01
+-----+-----+-----+-----+-----+-----+-----+-----+
|                DSCP               |    ECN    |
+-----+-----+-----+-----+-----+-----+-----+-----+

                        DSCP

name    dec tos binary      name    dec  tos binary
AF11    10   40 001010      CS1       8   32 001000
AF12    12   48 001100      CS2      16   64 010000
AF13    14   56 001110      CS3      24   96 011000
AF21    18   72 010010      CS4      32  128 100000
AF22    20   80 010100      CS5      40  160 101000
AF23    22   88 010110      CS6      48  192 110000
AF31    26  104 011010      CS7      56  224 111000 
AF32    28  112 011100      EF       46  184 101110
AF33    30  120 011110      default   0    0 000000
AF41    34  136 100010      
AF42    36  144 100100      AF = assured forwarding
AF43    38  152 100110      EF = expedited forwarding
                            CS = class selector

   ECN (unrelated to QoS)
   00   Not-ECT  Not ECN-Capable Transport
   01   ECT(0)   ECN-Capable Transport 
   10   ECT(1)   ECN-Capable Transport 
   11   CE       Congestion Experienced