Subject: doubt in sec. 2.8 and 2.9 of draft-ietf-pim-v2-sm-00.txt

From: Bhavesh Pathak <[email-masked]>
Date: Mon, 11 Oct 1999 06:36:11 -0700 (PDT)

Dear everybody,
 I am trying to understand draft-ietf-pim-v2-sm-00.txt. I am not 
 able to understand following.
 
 A.
 The section "2.8 Multicast data packet processing" says that,
 
 If the SPT-bit is cleared, then:
 
    1 if the incoming interface is the same as a matching
      (S,G) iif, the packet is forwarded to the oif-list of
      (S,G). In addition, the SPT bit is set for that entry if
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      the incoming interface differs from the incoming interface
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      of the (*,G) or (*,*,RP) entry.
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 Question: Why it is required that entry's incoming interfaces needs 
           to be from (*,G) or (*,*,RP) to set SPT bit?
 
 B.
 In the section "Parallel paths to a source or the RP--Assert process:"
 it says that:

 " In case the packet, or the Assert message, matches on oif for
    (*,*,RP) entry, a (*,G) entry is created, and asserts take place as
    if the matching state were (*,G)."
 
 Question: I am unable to understand why it is required to create 
           (*,G) entry? How does it help?
 
 -bhavesh

---

From: Pavlin Ivanov Radoslavov <[email-masked]>
Date: Mon, 11 Oct 1999 12:05:59 -0700

>       (S,G). In addition, the SPT bit is set for that entry if
                 ~~~~
              "...to be different from..."(?)

The SPT indicates a tree/entry rooted in the Source instead of the
RP.

>            (*,G) entry? How does it help?

The Asserts are with regard to a (S,G) or (*,G) entries only, so for
example, the loser of the (*,G) assert needs to have (*,G) entry to
prune the oif for that group only.

Pavlin

---

From: Liming Wei <[email-masked]>
Date: Mon, 11 Oct 1999 12:23:02 -0700 (PDT)

Bhavesh,

> From: Bhavesh Pathak <[email-masked]>
>  
>  Dear everybody,

The SPT bit is only relevant when the (S,G)'s iif is different from
that for the (*,G) or (*,*,RP). After a diverging router decides
to switch to Source tree (SPT) from a shared tree (RPT), it needs to
continue to forward packets down the RPT, even if the (S,G) alreaedy
exists and RPF fails on the (S,G) entry.

>            (*,G) entry? How does it help?

The assert relates to a particular group G, and may not apply for
other groups.

-Liming