From: Petr Lapukhov (petrsoft@gmail.com)
Date: Mon Mar 27 2006 - 03:52:24 GMT-3
Hello, Victor,
Okay, let's see.
First, there is a good link on cisco tech support:
http://www.cisco.com/en/US/tech/tk828/technologies_white_paper09186a00800d6b6
1.shtml
Now, As you recall, AutoRP use two dense-mode groups to disseminate RP
information. So we could face two problems here, actually:
1) MAs don't hear some of RPs announcements
2) Some of PIM routers miss MA discovery messages.
As usually with PIM-DM, these situations could be caused by RPF/OLIST
problems.
e.g. RP announce/discovery is being send from spoke (OLIST on hub)
or RP discovery arrives on non-RPF interface (RPF problem) (e.g. you have
multiple
routing protocols running on router, or highly redundant topology).
Another example would be when one of your spoke routers win Assert on
H&S topology, taking over hub router, and introducing OLIST problem.
As for BSR, it uses the same idea of flooding, checking for RPF/OLIST,
only difference being that it uses single 224.0.0.13 PIM address for that.
Now, general resolution guidelines:
1) RPF problem could be solved with static mroute, IGP metric/distance
adjustements.
2 ) OLIST problem could be solved with additional interface (e.g. tunnel) +
static mroute,
or with IGP metric/distance adjustement, if you need to change Assert
winner.
What about RP placement in PIM-SM? Obviously, if you place it on spoke, you
could
not be able to join shared-tree from another spoke, since hub will not
forward join
back the same interface.
You need either to configure tunnel, switch to p2p interfaces, or the best
part - use pim
nbma mode on hub. (Okay, pim-bidir will work here too, if hub is DF :)
With PIM NMBA, as I said, PIM actully behaves like it have p2p links
to every neighbor on NBMA network. It processes prune/joins separately, and
breaks standard OLIST problem.
HTH
Petr
2006/3/26, Victor Cappuccio <cvictor@protokolgroup.com>:
>
> Petr, thanks for the explanation, could you please go a little bit int
> detail in points 1 and 2, when running pim sparse over H&S,
> What if I'm not allowed to move the MA to another place? the ip mroute
> will be sufficient??
> and in point 2 I thought that the problem would be if Multicast Client
> Router to the MAgent fails the RPF Check
>
> Many Thanks
> Victor.
>
>
>
> Petr Lapukhov escribis:
>
> -- Sorry, repating e-mail to group address
>
> Hello David,
>
> If you run PIM Dense mode over FR H&S topology, you basically
> face an OLIST problem when you try to reach group joined on spoke
> from another spoke.
>
>
> Hub won't forward mpacket on the same interface it was received from.
> This problem could be solved with single tunnel (either R1-R2, R2-R3,
R1-R3)
>
> and proper static mroute on _receiving_ side of the tunnel (to prefer
tunnel
>
> over
> physical interface for sure).
>
> Now if you run PIM Sparse over H&S, you may face the same problem,
> and more.
>
> 1) You may miss BSR/AutoRP announces due to OLIST problem.
> 2) You may be unable to join shared tree if RP is places improperly (spoke)
>
> 3) You may face OLIST problem with mpacket delivery (the same as above).
>
> Leaving 1,2 aside, lets look at 3.
>
> For that mpacket OLIST problem, you may basically:
>
> 1) use tunnel/mroute, as in PIM-DM
>
> 2) use "pim nbma-mode" on hub multipoint interface,
> 3) enable PIM bidir mode to use bidirectional shared tree and place RP on
> hub
>
> HTH
> Petr
>
> 2006/3/26, david robin
> <robindavi@gmail.com> <robindavi@gmail.com>:
>
> dear all,
> I want to very something with ip multicast, if we have a frame-relay
> connection, R1 is the hub connected wih a multipoint interface to r2 and
> r3
> the spokes, the qusetion is if we had a multicast group on r2 fast
>
> ethernet
> ( using ip igmp join), the fact that I cant ping this multicast group from
> r3, does i have to configure tunnels ( 1 tunnel between r1 and r2 and 1
> tunnel between r1 and r3) in order to make the multicast packets flow ??
>
>
> Also there is another question in case i run pim sparse-dense as r1 is the
> RR the same problem will occur and does i have to configure tunnel too ???
>
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