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

Hi Ovidiu,

Great work! The attitude of a true expert! It is not true because some
guru said it, it is not true because you read it. Show, debug and capture
are the best teachers!

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 3:07 PM
> To: bob_at_bobsinclair.net
> Cc: Cisco certification; Cisco certification
> Subject: 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
> >>
> >>
> >> Blogs and organic groups at http://www.ccie.net
> >>
> >>
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Received on Sat Aug 21 2010 - 15:18:52 ART