Re: MSDP Multicasting

This might happen because of the nature of ICMP and a special IOS behavior.
When you send ICMP REQUEST from R5 it is naturally sent out of all PIM
interfaces (IOS implementation behavior) and it also registers on the RP. R4
receiving and processing this information might do the same, and once R2
knows about it, then you'll see this behaviour.

I'd suggest plugging another device on the link between R5 and R6, or
between R4 and R5 and doing the same again. The device could be either
normal PC (whatch TTL on those) or a router that does not have any multicast
enabled anywhere.

On Tue, May 19, 2009 at 3:17 PM, Garth Bryden <
hacked.the.planet.on.28.8k.dialup_at_gmail.com> wrote:

> Hi,
>
> Ok thanks, that part makes sense, but when you are statically setting your
> RP's like in this Lab i'm getting behaviour I would not expect too see
> running PIM-SM. This is behaviour I'd except with PIM-SDM or with the ip
> pim
> auto listener f
>
> For Example my Topology is like this
>
> [SW1] ---- (R3) ----- (R1) ------ (R2) ------- (R4) ------- (R5) ------
> (R6)
> ----- [SW2]
>
> Interfaces from SW1 to R2 are OSPF area 0
> Interfaces from R4 to SW2 are OSPF area 0
> There is no OSPF Link between R2 and R4
> EBGP between R2 and R4 advertising each AS's routes
>
> PIM Spare Mode Configured on all interfaces between SW1 to SW2
> R2 and R4 configured as RP for there Domains
> MSDP Linking R2 and R4.
>
> SW1 and SW2 join multicast group 224.1.1.1
> I perform an ICMP Ping from R5.
>
> The behaviour I expected was-
>
> A) With MSDP Configured; ICMP replies from both SW1 and SW2 *Yep works*
>
> B) With MSDP Not Configured; ICMP replies from only SW2 *Nope still replies
> from SW1 and SW2*
>
> I did not think this would happen in the case B because in PIM-SM I thought
> the Reciever and the Source had to join via the RP in this case R4 then
> they
> could create the SPT and have a direct stream. This made me believe that
> SW1
> would never be able to recieve the stream without MSDP being between R2 and
> R4 because the source being R5 would never join the RP for the domain that
> SW1 belongs too which is R2.
>
> In fact, I have noticed the first ICMP reply only comes back from SW2 but
> then the second ICMP reply comes back from SW2 and SW1.. When i did a
> debug,
> it seemed as if the PIM-SM RPs would flood the (S,G) information for
> 224.1.1.1 between R2 and R4 a characteristic, I only thought would have
> been
> seen running PIM-SDM.
>
> Does anyone have any insight as to why this would happen? I'm stumped!
>
> Thanks,
>
> Garth
>
> On Sun, May 17, 2009 at 11:12 PM, Peter Svidler <doubleccie_at_yahoo.com
> >wrote:
>
> >
> > The point of using MSDP is to inform certain domain about active sources
> in
> > another domain ,MSDP achieve this without exposing the RP of each domain
> to
> > serve the other domain.
> >
> > usually SP do not expose the domain RP to another domain by setting the
> > domain boudaries on the SP border links ( bsr-border for example) so that
> > you will not end up serving another domain with your own RP.
> >
> > you still need to enable PIM on the border links though in order to
> update
> > the outgoing interface list and allow the multicast traffic to pass
> between
> > the two domains .
> >
> > HTH
> >
> >
> >
> >
> >
> > --- On *Sun, 5/17/09, Garth Bryden <
> > hacked.the.planet.on.28.8k.dialup_at_gmail.com>* wrote:
> >
> >
> > From: Garth Bryden <hacked.the.planet.on.28.8k.dialup_at_gmail.com>
> > Subject: MSDP Multicasting
> > To: ccielab_at_groupstudy.com
> > Date: Sunday, May 17, 2009, 3:10 AM
> >
> > Hello GS,
> >
> > I am doing the IE Multicasting Technology Labs v4.1 at the moment. The
> MSDP
> > Lab in particular on page 74 and I need some help.
> >
> > I have the entire lab setup and running MSDP and PIM-SM between the
> > interfaces on R2 and R4, to really test this out I have joined SW1 and
> SW2
> > to the igmp group 224.1.1.1 and icmp'd the group address from R5. I get
> > replies from both switches and everything works just dandy.T
> >
> > Then to perform some further testing and to make sure it was definately
> > working correctly I took of the MSDP configuration, cleared all the
> > multicast routes and tested the scenario again, believing that I would
> only
> > get replies from SW2 which is in my local AS but this was not the case,
> > because there was a PIM-SM neighbor relationship between R2 and R4, R2
> sent
> > a join message to R4 and look out I'm up and running between two domains
> > without MSDP.
> >
> > Ok, so I figured that was silly, I should turn PIM-SM off the interfaces
> > between R2 and R4 then MSDP back on and then re-run both tests. I did
> that
> > and now i'm even more confused, the behaviour I got was when I sent
> through
> > the first ICMP to the group it went through and I got a reply from both
> > neighbors, after that the PIM-SM behaviour where the Receiver will create
> a
> > new SPT straight to the source was created instead of using the RP;
> because
> > of this behaviour the RP decides that there are no recipients for the
> > stream
> > coming through him anymore and sends a prune message, to which none ot
> the
> > multicast traffic is sent to R5 and therefore never forwarded across the
> > domain!
> >
> > So my query here is, what is the point of MSDP for interdomain
> connectivity
> > like this presented on the lab for interdomain connectivity if it works
> > with
> > PIM-SM without it... or is there something I'm missing with my MSDP
> > configuration to get around PIM-SM RP pruning itself from the tree after
> > the
> > first ICMP?
> >
> > I haven't worked my way up to multicast BGP but would this get around the
> > issue or would I have the same problems??
> >
> > Thanks in advance for your help GS!
> >
> > Regards,
> >
> > Garth
> >
> >
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