Good afternoon, I’m trying to understand the essence of the QoS working mechanisms and got into a misunderstanding of such concepts as traffic painting, coloring, color marking.Every article just mentions three flowers green yellow red, I understand that this is some kind of action with packages after passing the classification but I don’t understand what exactly it does and due to what.
  • just marking, instead of numbers with numbers - letters, or rather words, are clearly invented by"metrosexuals" – Angry Android Sep 30 '19 at 13:09

3 Answers 3

When packets pass through the network equipment port, they fall into a certain queue.There can be several queues on the port(some hardware, some software).The queues are configured, it is determined for them what they should do with the packets when certain thresholds are reached(read about basket token algorithm).For each queue, a traffic light is set(your colors are red, yellow, green) - boundary values.For each boundary value, actions are taken(shape, discard, shift to another queue, etc.).

Coloring a packet means assigning it some kind of QoS field(IPP/DSCP at the IP level, 802.1p on ethernet or EXP on MPLS).Based on this coloring, the packet is placed in one of the queues on the interface.This has nothing to do with red-yellow colors -green.
  • Thank! I’ll go read more about working with queues and other cisco manuals. – Yoshi's Landmine Sep 30 '19 at 13:52
Conventional traffic labeling by priority.
  • Is it possible for a beginner in the subject a little more in detail? How is it produced and what are the priorities? DSCP? Let’s say a bunch of packets with different DSCP values ​​in the header arrive at the interface, will they be marked by them? – Yoshi's Landmine Sep 30 '19 at 13:25
Traffic painting is a manipulation of DSCP, the DS(ToS) field in the IP packet, in addition to it there is also an ECN field in the same place.IP precedence can still be found, it's all there from ancient documents.
At the second level of Ethernet, this is the manipulation of the CoS field(802.1p) which appears in the specification of 802.1q wilans
The corresponding headers are in many other protocols, in MPLS, for example, this is the TC field.

The paint here is nothing more than a gross simplification.The number of colors for CoS is 8, and for DSCP as much as 64.And with 3 colors you won’t get rid of it.Of course there are certain conventions which traffic than to mark, in general, the higher the number, the higher priority traffic .

But, in fact, this does not mean anything, it's just a number.As the traffic advances, each individual node on the path decides for itself what to do with the traffic marked in one way or another.
  • Thank you, Michael, it became clearer! – Yoshi's Landmine Sep 30 '19 at 13:47