[pim] Bidir-PIM DF state transitions - events are not clear to understand the scenario and situation

[Sundara Moorthy M <[e-mail]>]

Hi Authors,

I am going through the RFC 5015 for BIDIR-PIM implementation.

DF election state machine mentioned in the table (Figure 3: Designated Forwarder election state machine in tabular form)
is not clear.

There is so many terms/terminologies used in the above said table, which are not clarified anywhere in the section:3.5.3 and also in section:3.5.2. Please find my queries below:


You have mentioned around 11 events. But I don't understand the meaning and the difference between the below mentioned events.

1. Recv better PASS/WIN
2. Recv PASS for us
3. Recv better BACK-OFF
4. Recv better BACK OFF for us
5. Recv worse PASS/WIN/BACK-OFF


How does the event 1 and event 2 differ from each other?

How does the event 3 and event 4 differ from each other?

When does the event 2 and event 4 occur(Highlighted in Blue in below table)??


In the below table, for the "Prev State: Lose" and the "event: Recv Better Offer", why is that state change required there(Highlighted in RED)?
Since the "Prev State: Lose" and the better offer event is received, it doesn't need to change the state and anyway its going to be in Lose state.

+-------------+------------------------------------------------------+
|             |                    Event                             |
| Prev State  +-----------------+------------------+-----------------+
|             | Recv better     | Recv better      | Recv better     |
|             | Pass / Win      | Backoff          | Offer           |
+-------------+-----------------+------------------+-----------------+
|             | -> Lose         | -                | -               |
| Offer       | DF = Sender or  | DFT = BOperiod   | DFT = OPhigh;   |
|             | Target; Stop    | + OPlow; MC =    | MC = 0          |
|             | DFT             | 0                |                 |
+-------------+-----------------+------------------+-----------------+
|             | -               | -                | -> Offer        |
| Lose        | DF = Sender or  | DF = Sender      | DFT = OPhigh;   |
|             | Target          |                  | MC = 0          |
+-------------+-----------------+------------------+-----------------+
|             | -> Lose         | -> Lose          | -> Backoff      |
|             | DF = Sender or  | DF = Sender;     | Set Best to     |
| Win         | Target; Stop    | Stop DFT         | Sender; Send    |
|             | DFT             |                  | Backoff; DFT =  |
|             |                 |                  | BOperiod        |
+-------------+-----------------+------------------+-----------------+
|             | -> Lose         | -> Lose          | -               |
|             | DF = Sender or  | DF = Sender;     | Set Best to     |
| Backoff     | Target; Stop    | Stop DFT         | Sender; Send    |
|             | DFT             |                  | Backoff; DFT =  |
|             |                 |                  | BOperiod        |
+-------------+-----------------+------------------+-----------------+




+-----------+-------------------------------------------------------+
|           | Event                                                 |
|           +-------------+-------------+--------------+------------+
|Prev State |Recv Backoff |Recv Pass    |Recv Worse    |Recv worse  |
|           |for us       |for us       |Pass / Win /  |Offer       |
|           |             |             |Backoff       |            |
+-----------+-------------+-------------+--------------+------------+
|           |-            |-> Win       |-             |-           |
|           |DFT =        |Stop DFT     |Set DF to     |DFT ?=      |
|Offer      |BOperiod +   |             |Sender or     |OPlow; MC = |
|           |OPlow; MC =  |             |Target; DFT   |0           |
|           |0            |             |?= OPlow; MC  |            |
|           |             |             |= 0           |            |
+-----------+-------------+-------------+--------------+------------+
|           |-> Offer     |-> Offer     |-> Offer      |-> Offer    |
|           |DF = Sender; |DF = Sender; |DF = Sender   |DFT = OPlow;|
|Lose       |DFT = OPlow; |DFT = OPlow; |or Target;    |MC = 0      |
|           |MC = 0       |MC = 0       |DFT = OPlow;  |            |
|           |             |             |MC = 0        |            |
+-----------+-------------+-------------+--------------+------------+
|           |-> Offer     |-> Offer     |-> Offer      |-           |
|           |DF = Sender; |DF = Sender; |DF = Sender   |Send Winner |
|Win        |DFT = OPlow; |DFT = OPlow; |or Target;    |            |
|           |MC = 0       |MC = 0       |DFT = OPlow;  |            |
|           |             |             |MC = 0        |            |
+-----------+-------------+-------------+--------------+------------+
|           |-> Offer     |-> Offer     |-> Offer      |-> Win      |
|           |DF = Sender; |DF = Sender; |DF = Sender   |Send Winner;|
|Backoff    |DFT = OPlow; |DFT = OPlow; |or Target;    |Stop DFT    |
|           |MC = 0       |MC = 0       |DFT = OPlow;  |            |
|           |             |MC = 0       |              |            |
+-----------+-------------+-------------+--------------+------------+



Thanks and Regards,
 Sundara Moorthy M


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