From: Arun Arumuganainar (aarumuga@hotmail.com)
Date: Tue Feb 28 2006 - 06:50:33 GMT-3
Pls. Note : " Sparse-mode with SPT-threshold set to infinity " does not
amount to Bi-dir PIM .
Normally PIM works like this .
1)When a new source comes up . It sends a unicast-register message to
the RP . Register-message is nothing but an encapsulated multicast packet
!!!
2) RP then de-capsulate it and the Floods it to rest of the multicast
domain following SPARSE_MODE rules .
3) Once register message crosses a threshold then RP will create
Source-tree with the source-PIM-router !!!
4) From there on Packet is forwarded to RP via source tree ( S,G) and
From RP to rest via Shared Tree (*,G) .
Note : After point 4 Receiver might also initiate a Source tree ( S,G)
directly to the source PIM router . But this Source tree formation depends
entirely on SPT-Threshold value .
Also Note here . In normal mode , Flow of Packets on shared tree is always
"***RP TO LEAF NODE (OR THE RECEIVERS)***" . Other way( Leaf node or source
to RP forwarding via shared tree ) is not possible at all . We will have to
fall back to register message or form a Source tree .
What will happen in BIDIR mode is largely different ....
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Register message is totally done away with !!! Source can directly send the
Multicast packet to RP using the very same Shared tree ( *,G) . Here
Forwarding happens like this .
1) When a new source comes up , the leaf pim router forwards it to RP
using the shared tree itself .
2) When RP receives a Multicast part , it sends it back to the rest of
the shared Tree
Pls. Note : Here Packets moves in both direction on the shared tree i.e
Source PIM Router to RP and also RP to Receiver PIM Router . Only because of
this it gets the name "***PIM BI-DIR***"
Also note that when SPT threshold is properly set than Source tree formation
between receiver and Source would still happen in BI-DIR mode also.
Thanks and Regards
Arun
----- Original Message -----
From: "McCallum, Robert" <robert.mccallum@thus.net>
To: "CCIEin2006" <ciscocciein2006@gmail.com>; "Bob Sinclair"
<bob@bobsinclair.net>
Cc: <ccielab@groupstudy.com>
Sent: Tuesday, February 28, 2006 3:26 AM
Subject: RE: Difference between Bidirectional PIM and PIM Sparse Mode
> Yip but with a few differences ;-)
>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
> > Behalf Of CCIEin2006
> > Sent: 27 February 2006 21:29
> > To: Bob Sinclair
> > Cc: ccielab@groupstudy.com
> > Subject: Re: Difference between Bidirectional PIM and PIM Sparse Mode
> >
> > Hmm kinda sounds like sparse mode with the spt-threshold set
> > to infinity....
> >
> > On 2/27/06, Bob Sinclair <bob@bobsinclair.net> wrote:
> > >
> > > BIDIR is a strange beast:
> > >
> > > Unlike Dense mode, Bidir does not flood to all PIM
> > neighbors, only up
> > > the shortest path tree to the RP. If there are no clients who want
> > > traffic, then Dense will prune back. BIDIR only prunes back to the
> > > RP, then the RP drop it. Traffic continues to be forwarded
> > from the
> > > source to the RP as long as it is active. Receivers join
> > much like regular sparse-mode:
> > > explicit joins toward the RP.
> > >
> > > BIDIR is a lot like spanning-tree: think of RPF interface as root
> > > port; think of DF interface as designated port. Basic rule
> > then is if
> > > a port is not RPF or DF, then it cannot forward for the group. In
> > > fact, BIDIR is similar to Core Based Tree, which Radia
> > Perlman had a hand in developing.
> > >
> > > Good for many-to-many multicast because it minimizes state.
> > >
> > > Try labbing it up and doing some "debug ip mpacket". Just enable
> > > globally (ip pim bidir-enable) and add the "bidir" keyword
> > to your RP
> > > statements.
> > >
> > >
> > > Bob Sinclair
> > > CCIE #10427, CCSI 30427
> > > www.netmasterclass.net
> > >
> > >
> > > ----- Original Message -----
> > > *From:* CCIEin2006 <ciscocciein2006@gmail.com>
> > > *To:* Bob Sinclair <bob@bobsinclair.net>
> > > *Cc:* ccielab@groupstudy.com
> > > *Sent:* Monday, February 27, 2006 1:24 PM
> > > *Subject:* Re: Difference between Bidirectional PIM and PIM Sparse
> > > Mode
> > >
> > >
> > > Hi Bob,
> > >
> > > Since the first hop routers forward the traffic whether its
> > wanted or
> > > not, isn't that like dense mode?
> > >
> > > Do receivers still send joins to the RP?
> > >
> > > What does the RP do with the traffic if there are no
> > receivers - send
> > > a prune?
> > >
> > > Thanks!
> > >
> > > On 2/27/06, Bob Sinclair <bob@bobsinclair.net> wrote:
> > > >
> > > > Bidirectional PIM Differs from Sparse mode in at least these ways:
> > > >
> > > > Bidir does not maintain any (S,G) state. Only (*,G)
> > state. This is
> > > what
> > > > makes it scalable for many-to-may multicast.
> > > >
> > > > Bidir does not do PIM registration. First-hop routers do not
> > > > register traffic with the RP. First hop routers, forward traffic
> > > > for active
> > > groups
> > > > toward the RP, whether anyone wants the traffic or not,
> > as long as
> > > > the
> > > group
> > > > is active.
> > > >
> > > > Since there is no PIM registration, the RP does not
> > actually have to
> > > > be
> > > a
> > > > reachable address, only a reachable network that acts as a root.
> > > >
> > > > Here is a link with more info:
> > > >
> > > >
> > > >
> > >
> > >
> > http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/product
> > s_configuration
> > > _guide_chapter09186a00800ca796.html
> > > >
> > > >
> > > > HTH,
> > > >
> > > > Bob Sinclair
> > > > CCIE #10427, CCSI 30427
> > > > www.netmasterclass.net
> > > >
> > > >
> > > > ----- Original Message -----
> > > > *From:* CCIEin2006 <ciscocciein2006@gmail.com>
> > > > *To:* ccielab@groupstudy.com
> > > > *Sent:* Monday, February 27, 2006 11:28 AM
> > > > *Subject:* Difference between Bidirectional PIM and PIM
> > Sparse Mode
> > > >
> > > >
> > > > Hello group,
> > > >
> > > > I am not very clear on the differences between
> > Bidirectional PIM and
> > > > PIM Sparse Mode. Both use the RP and switchover to shortest path
> > > > tree after the first packet is received, correct?
> > > >
> > > > How do they differ exactly?
> > > >
> > > >
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