Subject: [pim] Need clarfication on PIM join/prune echo

From: byungki lee <[email-masked]>
Date: Wed, 19 May 2010 12:38:48 +0900

Hi,

I need clarification on router behavior when receiving PIM prune echo. When
upstream router (R1) echoes prune message from one spoke (R2-1) to the other
(R2-2), should it change source address as R1 interface to meet the
requirement below?

4.5.  PIM Join/Prune Messages

In general, a PIM Join/Prune message should only be accepted for processing
if it comes from a known PIM neighbor.  A PIM router hears about PIM
neighbors through PIM Hello messages.  If a router receives a Join/Prune
message from a particular IP source address and it has not seen a PIM Hello
message from that source address, then the Join/Prune message SHOULD be
discarded without further processing.

I believe so, otherwise, R2 should discard that "echoed" prune message
because that message is not coming from it's PIM neighbor. Is it clear?

Regards,

Byung

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From: Indranil Bhattacharya <[email-masked]>
Date: Wed, 19 May 2010 09:41:17 +0530

Hi Byung,

              Yes, you are correct.

Excerpt from "Prune-Pending Timer Expires" in "4.5.1.  Receiving (*,*,RP)
Join/Prune Messages" is given below:

"A PruneEcho(*,*,RP) is simply a Prune(*,*,RP) message sent by the upstream
router on a LAN with its own address in
          the Upstream Neighbor Address field."

Resaon is mentioned in  "Prune(*,*,RP) to MRIB.next_hop(RP)"  in "4.5.5.
Sending (*,*,RP) Join/Prune Messages".
Thanks,
Indranil
On Wed, May 19, 2010 at 9:08 AM, byungki lee <[email-masked]> wrote:

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From: byungki lee <[email-masked]>
Date: Wed, 19 May 2010 13:53:38 +0900

Hi Indranil,

Thank you for the reply.

It's clear to change IP address in the Upstream Neighbor Address field. How
about source IP address field of the echoed prune message? Shouldn't it be
changed as the Upstream router IP address as well?

Thanks,
Byung

2010/5/19, Indranil Bhattacharya <[email-masked]>:
>> I need clarification on router behavior when receiving PIM prune echo.
>> When upstream router (R1) echoes prune message from one spoke (R2-1) to the
>> other (R2-2), should it change source address as R1 interface to meet the
>> requirement below?
>>
>> In general, a PIM Join/Prune message should only be accepted for
>> processing if it comes from a known PIM neighbor.  A PIM router hears about
>> PIM neighbors through PIM Hello messages.  If a router receives a Join/Prune

---

From: Everton Marques <[email-masked]>
Date: Wed, 19 May 2010 11:52:44 -0300

>From the description below, I take the PruneEcho should be sent only
on the same interface/spoke the Prune has been received, no?

--xx--

[RFC4601] 4.5.3.  Receiving (S,G) Join/Prune Messages
(...)
Transitions from Prune-Pending State
(...)
Prune-Pending Timer Expires

The Prune-Pending Timer for the (S,G) downstream
state machine on interface I expires.

The (S,G) downstream state machine on interface I
transitions to the NoInfo state.  A PruneEcho(S,G)
is sent onto the subnet connected to interface I.

The action "Send PruneEcho(S,G)" is triggered when
the router stops forwarding on an interface as a
result of a prune.  A PruneEcho(S,G) is simply a
Prune(S,G) message sent by the upstream router on
a LAN with its own address in the Upstream Neighbor
Address field.

--xx--

Everton

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From: byungki lee <[email-masked]>
Date: Thu, 20 May 2010 09:32:22 +0900

OK. Let me describe the question with example.

           ------
          | R1 |
           ------
             |1.1.1.1/24
    ---------------------
    |1.1.1.2/24     |1.1.1.3/24
  ------              ------
  |R2-1|          |R2-2|
  ------              ------

The PIM neighbors are formed between R1 and R2-1, R1 and R2-2. No PIM
neighbor between R2-1 and R2-2. (NBMA environment)

When R2-2 sends prune, R1 should send prune echo to R2-1. There is no doubt
the upstream neighbor address field should be 1.1.1.1 in the prune echo
packet.

The question is source IP address of the prune echo packet sent by R1.

My understanding is if the source IP address of the prune echo packet is
1.1.1.3 (No change from the original prune packet), R2-1 should discard the
packet because that prune does not come from its PIM neighbor. (R2-1 forms
neighbor only with R1(1.1.1.1)). So When R1 sends prune echo, R1 should
change the source IP address with 1.1.1.1. Is my understanding correct?

Thanks,
Byung

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From: Indranil Bhattacharya <[email-masked]>
Date: Thu, 20 May 2010 17:09:20 +0530

Hi Byung,

              If you are operating on an NBMA network then there is no need
to send PIM-PRUNE-ECHO. If you are operating on NBMA mode (ip pim nbma) then
the router considers all remote sites as different oifs. Thus you have
point-to-point link and it is mentioned that on a point-to-point link there
is no need to send pim-echo. Please refer the below article:

http://www.cisco.com/en/US/docs/ios/solutions_docs/ip_multicast/White_papers/frm_rlay.html

              If the above feature is not there in your router then yes
source address needs to be changed.

Thanks,
Indranil

On Thu, May 20, 2010 at 6:02 AM, byungki lee <[email-masked]> wrote:

>> On Wed, May 19, 2010 at 12:38 AM, byungki lee <[email-masked]>wrote:
>>
>>>

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From: Rajesh Nataraja <[email-masked]>
Date: Thu, 20 May 2010 10:31:56 -0700

Hi Byung,

In the first place, I believe the PruneEcho should always be sent with
Source IP address of R1 and not that of the previously pruning downstream
neighbor.

Thanks
Rajesh.

On Thu, May 20, 2010 at 4:39 AM, Indranil Bhattacharya <
[email-masked]> wrote:

>> When R2-2 sends prune, R1 should send prune echo to R2-1. There is no
>> doubt the upstream neighbor address field should be 1.1.1.1 in the prune
>> echo packet.
>>