Subject: [pim] pim-sm-v2-new-09 and PMBR issues

From: Pekka Savola <[email-masked]>
Date: Sat, 20 Mar 2004 17:37:56 +0200 (EET)

Hi,

(I read through the pim spec, and I'll be writing up my comments in a 
couple of days .. but there's one biggest issue which I wanted to 
raise immediately..)

Section 4.7 defines the behaviour of PIM-SM router which is 
interfacing a different multicast routing protocol, referring to RFC 
2715.

Issue 1: the whole point may be moot because RFC 2715 is
Informational, and this is aimed aa Standards Track; there can be no
normative reference to it.

Possible resolution: decrease the weight of RFC 2715 in this document,
and move RFC 2715 off to informative references.

Issue 2: the wildcard receiver requirement (see below) is completely
unrealistic, could be an enermous DoS component, and is completely
inpractical -- not to mention failing to work with mechanisms like
SSM, Embedded-RP or Bidir-PIM (?) -- where a random edge router does
not know about all the groups in a domain.  Imagine a case where you
could associate with a PIM-SM router, and act as a wildcard receiver.  
Instand multicast DoS as the PIM-SM router would have to join to every
source in the Internet!!!! 

Suggestion: discuss this requirement.  My feeling is that it should be
deprecated (with caveats, and describing its limitations) or removed
completely.

============
4.7.2.  Sources Internal to the PIM-SM Domain

A PMBR needs to ensure that traffic from sources inside the PIM-SM
domain reaches receivers outside the domain.  Using terminology from RFC
2715, there are two possible scenarios for this:

o Another component of the PMBR is a wildcard receiver.  In this case
  the PIM-SM component of the PMBR must ensure that traffic from all
  internal sources reaches the PMBR until it is informed otherwise.

o No other component of the PMBR is a wildcard receiver.  In this case
  the PMBR will receive explicit information as to which groups or 
  (source,group) pairs the external domains wish to receive.

In the former case, the PMBR will need to send a Join(*,*,RP) to all the
RPs in the PIM-SM domain.  This will cause all traffic in the domain to 
reach the PMBR.  The PMBR may then act as if it were a DR with directly
connected receivers, and trigger the transition to a shortest path tree
(see Section 4.2.1).

In the latter case, the PMBR will not need to send Join(*,*,RP)
messages.  However the PMBR will still need to act as a DR with directly
connected receivers on behalf of the external receivers in terms of
=========

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

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