Subject: PIM-SM RP states

From: Siddiqui Zia-czs014 <[email-masked]>
Date: Mon, 19 Feb 2001 12:46:41 -0600

Greetings Folks,

A few quick questions on PIM-SM. Please advise.

1. If an RP receives a (*,G) JOIN for a group for which the RP already has a (S,G) entry for the source of that group. What is the state maintained for the shared tree by the RP. Is it (*,G)?

2. Do RPs always send C-RP advertisements for a group after having received a REGISTER for that group from a source?

Any info would be appreciated. Thanks

-Zia

---

From: Dino Farinacci <[email-masked]>
Date: Mon, 19 Feb 2001 12:10:38 -0800

>> 1. If an RP receives a (*,G) JOIN for a group for which the RP already has a (S,G) entry for the source of that group. What is the state maintained for the shared tree by the RP. Is it (*,G)?

    An RP can't send a (*,G) anywhere if indeed it is the RP for G, since it
    is the root of the shared tree for group G.

>> 2. Do RPs always send C-RP advertisements for a group after having received a REGISTER for that group from a source?

    The only way an RP can receive a Register is if other PIM routers in the
    domain know it's the RP for the given group. For them to know, the RP
    must have previously sent Candidate-RP messages, so the Bootstrap router,
    in turn, could distribute the group-to-RP mapping in Bootstrap messages 
    throughout the PIM domain.

Dino

---

From: helmy <[email-masked]>
Date: Mon, 19 Feb 2001 20:24:10 -0800 (PST)

> 1. If an RP receives a (*,G) JOIN for a group for which the RP already
has a (S,G) entry for the source of that group. What is the state
maintained for the shared tree by the RP. Is it (*,G)?

I believe both states should be maintained, with longest match rules used
for forwarding packets, (S,G) packets flow down S,G state, and others sent
to G (not sourced by S) are forwarded down (*,G)

> 2. Do RPs always send C-RP advertisements for a group after having
received a REGISTER for that group from a source?

C-RP advertisement are sent towards the bootstrap router (BSR) as soon as
a bootstrap message (carrying the elected BSR's identity) is received by a
router configured as candidate RP. Of course, damping is recommended to
avoid multiple C-RP Advs during transients (i.e. during election of a new
BSR),

Regards,
-A