Kevin Dorrell, CCIE #20765

28 Feb 2008

NMC Lab 09.18 – Multicast

Filed under: IP Multicast — dorreke @ 09:12

Started to work on the multicast again yesterday evening, but got hopelessly confused.  So much so I decided not to publish the blog.  Looking at yesterday’s posting, that was confused as well.  I shall have to tackle it with a clearer head.  I must do some multicast reading first though.  Wendell Odom’s CCIE Cert Guide, and Jeff Doyle’s book, Vol 2.  I shall add a few notes here as I go:

Multicast on LAN

  • IN PIM-DM, the winner of the “assert” contention is responsible for trasmitting the stream onto the LAN.  Assert is won by who is closest to the source (but is it pre-emptive?), with lowest IP as tie-breaker.
  • IGMP v1 uses PIM DR to determine who puts the IGMP query on the LAN.  It is the highest ip pim dr-priority, else the highest PIM IP address on the LAN.
  • IGMP v2 uses assert winner to query the LAN.  (Lowest IP as tie-breaker, so tutt’altro che DR).

PIM-SM RP – Rendez-Vous Point

Everyone should know where the RP is, by one of:

PIM-SM Source registration

  • If a router has a source, it sends a PIM register to the RP.  (The PIM register also encapsulates the first packet.  So why do we often not see a response from the RP to that first packet?)
  • If the RP has no listeners for that group, it sends a uncast Register-Stop back to the source.  Source router supresses register messages for 60 seconds.  After 55 seconds it sends a Null register with no packet encapsulated.

 To investigate:

  1. What happens if you declare dense-mode at one end of a link and sparse-mode at the other?

——————- Unfinished ————————


1 Comment »

  1. What parts of multicast are you having trouble with?

    Comment by D — 28 Feb 2008 @ 12:37

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