[Q] Leave Latency: Knowledge Confirmation

["Lee Jiwoong" <porce@kaist.ac.kr>]

Dear Seniors: Please check the correctness of my knowledge. A bit emergent
one. :)

I have a question on LEAVE LATENCY of IGMP (with DVMRP/PIM-DM.)

Topology:     N1---N2---N3---N4

Assume N1 is a server and N4 is the leaf receiver. N4 is receiving
multicast traffic initially.

---Plz check the correctness number-by-number---

1. According to my understanding of IGMPv2, if N4 "leaves group," N3 sends
"Last Membership Query" to outgoing interface.
2. N3 waits for any answer from leaf receivers. If there is no answer for
"given time", N3 prunes N4 and sends "Leave Group" message to N2.
3. Above "given time" is at least 2 seconds for IGMPv2. By default. (?).
4. This means N3-N4 link will have multicast traffic for at least 2 seconds
even after N4 leaves group.
5. After N3 sends "Leave Group" to N2, N2 sends "Last Membership Query" to
N3. Now it requires at least 2 seconds that N2-N3 link does not have
multicast traffic for that group, again.
6. The same to N1-N2 link.
7. Therefore, in order for "prune-requested traffic" not to flow through N1-
N4 links, at least 6 seconds is required after N4 actually leaves group.

-------------------------------------------------  Correct ?

Thanks in Adv.


Lee Jiwoong. KAIST

///////////////////////
// Lee, Jiwoong
// porce@kaist.ac.kr
// Word, would-be MVP