Re: (*,G) entries upstream of the RP in sparse mode

Thank you again Bob
I dig more into it and some debugs confirm this. I labbed in pim dense
and pim sparse mode the topology and here is my findings with debug ip
mrouting on R1 when generating pings to 224.1.1.1 from Source

topology: Source-R1-R2-R3-R4-R5-Receiver
PIM-DM
MRT(0): Create (*,224.1.1.1), RPF /0.0.0.0 <<-- this creats the (*,G) entry
MRT(0): RPF lookup for 10.10.10.1[0.0.0.0] (10.10.10.1) returned
FastEthernet0/0 10.10.10.1
MRT(0): Create (10.10.10.1,224.1.1.1), RPF FastEthernet0/0/0.0.0.0
<<--this creates the (S,G) entry
R1#sh ip mroute
(*, 224.1.1.1), 00:03:32/stopped, RP 0.0.0.0, flags: D
  Incoming interface: Null, RPF nbr 0.0.0.0
  Outgoing interface list:
    Serial1/1, Forward/Dense, 00:00:35/00:00:00

(10.10.10.1, 224.1.1.1), 00:00:10/00:02:55, flags: T
  Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0
  Outgoing interface list:
    Serial1/1, Forward/Dense, 00:00:10/00:00:00

PIM-SM:
MRT(0): RPF lookup for 3.3.3.3[0.0.0.0] (3.3.3.3) returned Serial1/1 12.12.12.2
MRT(0): Create (*,224.1.1.1), RPF Serial1/1/12.12.12.2 <<-- this
creats the (*,G) entry
MRT(0): RPF lookup for 10.10.10.1[0.0.0.0] (10.10.10.1) returned
FastEthernet0/0 10.10.10.1
MRT(0): Set the F-flag for (*, 224.1.1.1)
MRT(0): Set the F-flag for (10.10.10.1, 224.1.1.1)
MRT(0): Create (10.10.10.1,224.1.1.1), RPF FastEthernet0/0/0.0.0.0
<<--this creates the (S,G) entry

R1#sh ip mroute
(*, 224.1.1.1), 00:06:01/stopped, RP 3.3.3.3, flags: SPF
  Incoming interface: Serial1/1, RPF nbr 12.12.12.2
  Outgoing interface list: Null

(10.10.10.1, 224.1.1.1), 00:06:01/00:00:40, flags: FT
  Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0, Registering
  Outgoing interface list:
    Serial1/1, Forward/Sparse, 00:06:01/00:03:22
br
Ovidiu

On Sat, Aug 21, 2010 at 6:45 PM, Bob Sinclair <bob_at_bobsinclair.net> wrote:
> Hello Ovidiu,
>
> In sparse mode in Cisco IOS the (*,G) entry is created when:
>
> 1. a router receives an IGMP membership report from a client or a
> PIM join message from a downstream router
> 2. a multicast stream is detected and (S,G) state must be created
>
> The exception is source specific multicast, in which no (*,G) state is
> maintained.
>
> As you suggest, the (*,G) shared tree is not used to distribute traffic
> between the source and the RP and is unnecessary.
>
> The (*,G) entry is not used to distribute traffic in dense mode; it is
> simply a parent data structure for the (S,G), so I do not believe it is
> related to dense mode fallback.
>
> HTH,
>
> Bob Sinclair CCIE 10427 CCSI 30427
> CIERS2 Online Instructor
> www.tinyurl.com/ciers2online
>
>> -----Original Message-----
>> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
>> Ovidiu Neghina
>> Sent: Saturday, August 21, 2010 6:46 AM
>> To: Cisco certification; Cisco certification
>> Subject: (*,G) entries upstream of the RP in sparse mode
>>
>> Hi
>> I have a short question.
>> we have a sparse mode scenario with static RP - R3 with this topology
>> from antonio soares lab:
>> http://ccie18473.net/dynamips/dynamips.htm#pim-sm
>> Topology is : Source-R1-R2-R3-R4-R5-Receiver
>> Why do we have on R1, and R2 (*,G ) entries when sending traffic from
>> the source ? I know that is normal to have it dowstream of the RP but
>> i don't understand whey we have it upstream of the RP ? Is it for
>> dense mode fallback ?
>>
>> R1#sh ip mroute 224.1.1.1
>> (*, 224.1.1.1), 00:00:26/stopped, RP 3.3.3.3, flags: SPF
>> Incoming interface: Serial1/1, RPF nbr 12.12.12.2
>> Outgoing interface list: Null
>> (10.10.10.1, 224.1.1.1), 00:00:26/00:03:28, flags: FT
>> Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0
>> Outgoing interface list:
>> Serial1/1, Forward/Sparse, 00:00:26/00:03:04
>>
>> br
>> Ovidiu
>>
>>
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Received on Sat Aug 21 2010 - 22:06:37 ART