How many VLAN IDs are required for 802.1CB seamless redundancy?

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1 How many AN IDs are required for 802.1CB seamless redundancy? Norman Finn ersion 2 Mar. 4, 2014 cb-nfinn-how-many-ans-0214-v02.pdf 1

2 This presentation is cb-nfinn-how-many- ANs-0214-v02.pdf. It is based on the layering model presented in tsn-nfinn-2-data-plane-0214-v04. It also draws from tsn-nfinn-day-in-the-ife v02. cb-nfinn-how-many-ans-0214-v02.pdf 2

3 cb-nfinn-how-many-ans-0214-v02.pdf 3

4 Host Higher ayers work as always. Sequence number generation and discard can detect missing packets, discard duplicate or misordered packets, and/or correct packet ordering. Split S replicates and relabels packets circuit_identifiers. Merge M only relabels. Circuit Encaps/Decaps E / D packs/unpacks parameters in packets. 2-Data-Plane Q Q S E Higher ayers Sequencing Split / Merge Circuit Encaps/Decaps M D cb-nfinn-how-many-ans-0214-v02.pdf 4

5 b,c Relay Relay + circuit_identifier x a a Relay a D E E D E D E D D E D E S M E D Port Port Port Port Port Port to host to host to host a b 1 c a b 2 c a b 3 c Some ways to describe splitting and merging: 1. Split/Merge replicates packets and remaps circuit_identifier a to b and c on the way up. 2. Relay transfers circuit_identifier x along with packet among independent Encaps/Decaps. 3. Per-exit-port per-flow encapsulation remap a b and a c. E D Port E D Port cb-nfinn-how-many-ans-0214-v02.pdf 5

6 Bridge relay Port Port Port No matter how you describe it in detail, the observables outside the bridge are the same. If the different paths have different external encapsulations, then the bridge has to do percircuit remapping of those encapsulations. If all paths have the same external encapsulations, then the bridge does its ordinary job. cb-nfinn-how-many-ans-0214-v02.pdf 6

7 Choice 1: Split/Merge is the Bridge relay, functioning as normal, so the root and N paths all have the same {ID,DA} pair (circuit label), at least within a single bridge. Choice 2: Split/Merge replicate and reconcile different {ID,DA} pairs for each circuit (root and N paths), and the Bridge relay functions as normal. Not a choice: A new kind of Bridge relay. cb-nfinn-how-many-ans-0214-v02.pdf 7

8 Choice 1 {,D} 1 {,D} 1 {,D} 1 T R R {,D} 1 {,D} 1 Split/Merge functions S Bridge relay function R. {,D} 1 are the normal The flow has the same {AN ID, Destination MAC address} circuit identifier on both paths and at both ends. (Note: two frames output after the merge.) M cb-nfinn-how-many-ans-0214-v02.pdf 8

9 Choice 2 {,D} 2 {,D} 2 {,D} 1 T S R R M {,D} 1 {,D} 3 {,D} 3 Split functions S changes input {ID, DA} to different values for the two (or more) paths. Merge function M combines different circuit IDs into a third circuit ID. (Extra frames are eliminated by Sequence discard.) Each path has a different {ID, DA} pair, perhaps different from the outer pairs. cb-nfinn-how-many-ans-0214-v02.pdf 9

10 cb-nfinn-how-many-ans-0214-v02.pdf 10

11 T R R The Split / Merge function is a relay function Only these ports are enabled to pass the one {ID,DA} pair. If the Sequence Discard function is in the istener, then the istener typically receives two copies of every frame. R cb-nfinn-how-many-ans-0214-v02.pdf 11

12 T R R Only three ports are enabled to pass the one {ID,DA} pair. If the Sequence Discard is in the Bridge, then the istener typically receives only one copy of every frame. cb-nfinn-how-many-ans-0214-v02.pdf 12

13 T R R R R Intermediate Split/Merge functions work. Only green ports pass the flow. Sequenc discard eliminates duplicates. cb-nfinn-how-many-ans-0214-v02.pdf 13

14 T R R R But, what if the circuits collide? T R R R Which flow is right? cb-nfinn-how-many-ans-0214-v02.pdf 14

15 T R R R Won t we get extra copies of everything? Well, yes. Unless cb-nfinn-how-many-ans-0214-v02.pdf 15

16 T R R R You get extra copies unless you supply the necessary Sequence Discard functions. So no, you do no criss-cross the circuits. You do a one-box re-split re-merge. cb-nfinn-how-many-ans-0214-v02.pdf 16

17 ID=9 T Q S R R ID=7 ID=5 Choice 2 requires placing the Split S Merge M functions on the right ports. M ID=7 and cb-nfinn-how-many-ans-0214-v02.pdf 17

18 ID=9 T Q S R R M ID=7 ID=7 ID=5 As for Choice 1, the Sequencing functions Q, can be at either end of the host links. cb-nfinn-how-many-ans-0214-v02.pdf 18

19 ID=9 S M T S R R ID=7 S M ID=5 There are issues, however, when you try to do the intermediate Split/Merge. The upper center bridge must change ID 5 to ID 9, and the lower center bridge must change ID 9 to ID 5, all on their output ports. (And/or, change the DAs.) M ID=7 cb-nfinn-how-many-ans-0214-v02.pdf 19

20 S M T S R R ID=7 ID=9 ID=5 S But, what if there is some other Flow that also uses ID 5, and it does not need to be remapped? M You would have to do per-flow Circuit ID translation. Of course, that s what the Merge function M does, anyway.?? M ID=7 cb-nfinn-how-many-ans-0214-v02.pdf 20

21 ?? ID=9 S M T S R R ID=7 S M ID=5 It may be mathematically possible to label all ports in the network as either a red or a blue port, so this problem never comes up. M ID=7 cb-nfinn-how-many-ans-0214-v02.pdf 21

22 T R R R R But, it appears to this author that Choice 1 is a lot easier. cb-nfinn-how-many-ans-0214-v02.pdf 22

23 T A single AN also works for overlapping distribution, as in the ring, above. (Packets go both clockwise and counterclockwise.) We then depend upon the fact that a multicast is never transmitted on the port on which it was received. cb-nfinn-how-many-ans-0214-v02.pdf 23

24 T Clearly, two ANs work, also. Some discussion is in order to decide whether there are significant control plane advantages to using two ANs. (If we never flood, it doesn t seem to matter, much.) cb-nfinn-how-many-ans-0214-v02.pdf 24

25 Doesn t choice 1 enable a misconfiguration that could blow up the network with a multicast storm caused by a circular path? It seems slightly more probable that Choice 1 would blow up than Choice 2; but both can blow up. To ensure against loops, you would need a new pair of ANs (or DAs) at every hop. The requirement for AN IDs or DA remapping would be large. In either case, when using pinned-down paths, input filters that block frames from arriving on unexpected ports are an important safety feature against broadcast storms. cb-nfinn-how-many-ans-0214-v02.pdf 25

26 X? ID=9 X? ID=7 X? ID=5 R M ID=7 We must detect the situation where one path has failed, but not both, so that we have no protection. This is latent error detection. It is easier to identify which leg has the problem at the merge sequence point, if the paths have different labels? Yes. X? ID=7 R ID=7 cb-nfinn-how-many-ans-0214-v02.pdf 26

27 ID=9 X? X? X? X? X? ID=7 X? But, you also have to figure out where the error occurred, and the different IDs are no help, there. cb-nfinn-how-many-ans-0214-v02.pdf 27

28 cb-nfinn-how-many-ans-0214-v02.pdf 28

29 You can use one {ID, DA} circuit label pair for all of the sub-flows making up a stream protected by seamless redundancy. Doing so makes life simpler for the data plane, and avoids the need to teach a bridge how to do per-flow ID translation or destination address remapping. There may be control plane reasons to prefer more than one ID or DA. This author favors the use of one circuit label for all paths of a flow. cb-nfinn-how-many-ans-0214-v02.pdf 29

30 Thank you.

Layering for the TSN Layer 2 Data Plane

Layering for the TSN Layer 2 Data Plane Norman Finn Version 3 Feb. 17, 2014 tsn-nfinn-l2-data-plane-0214-v03.pdf 1 At the AVnu face-to-face meeting in December, Norm Finn made presentations on the subject