Re: Multicast Features

From: Paul Cosgrove (paul.cosgrove@heanet.ie)
Date: Tue Jul 08 2008 - 14:11:33 ART

Hi Joe,

I don't understand your suggested topology here, can you explain what
you are suggesting using multicast helper map for? Maybe you mean ip
sla there.

Depending on how you originate the traffic, the source device may send
the multicast traffic out all interfaces, but that device is not
performing multicast routing.

Receiving routers, if they have only sparse mode interfaces and no
connected devices which have joined the group, will treat the group as
dense and reply with a prune on the incoming interface. They will send
the traffic out any other interface.

So if your only receiver is two hops from the sender it will not receive
the traffic.

Paul.

Joseph Brunner wrote:
> right, but in my experience
>
>
>
> "but i believe it only truly goes to dense-mode if an RP is
> not known, right?"
>
>
>
> it does this even in a network where every interface is SM only.
>
>
>
> Try SM with just the multicast helper map feature making a feed run
> constantly (yes remember to disable control-packets)
>
> the see how the group looks with and without a known rp, oh, and make sure
> you have a receiver down the line with
>
> ip igmp join-group 224.x.y.z
>
>
>
> -Joe
>
>
>
> _____
>
> From: Harindha Fernando [mailto:pottaharry@gmail.com]
> Sent: Tuesday, July 08, 2008 10:45 AM
> To: Learn Cisco
> Cc: Joseph Brunner; John; ccielab@groupstudy.com
> Subject: Re: Multicast Features
>
>
>
> my understanding also same,
>
> On Tue, Jul 8, 2008 at 5:29 PM, Learn Cisco <cisco.learn@yahoo.com> wrote:
>
> i believe it reverts to a source-based tree after consulting the RP for each
> multicast session, but i believe it only truly goes to dense-mode if an RP
> is
> not known, right?
>
>
>
>
> ----- Original Message ----
> From: Harindha Fernando
> <pottaharry@gmail.com>
>
> To: Joseph Brunner <joe@affirmedsystems.com>
> Cc: John
> <jgarrison1@austin.rr.com>; Learn Cisco <cisco.learn@yahoo.com>;
> ccielab@groupstudy.com
>
> Sent: Tuesday, July 8, 2008 4:33:14 AM
> Subject: Re:
> Multicast Features
>
> I checked on the lab
>
> show ip multicast
>
> will give u the
> fallback mode
>
> 224.0.1.40 and 224.0.1.39 is for auto-rp rp announce and rp
> discovery
> (mapping agent), it will be in dense mode if you have configured IP
> PIM
> SM-DM but if you have only PIM SM configured on interface then you need ip
> pim autorp listener to allow autorp packets to cross sparse mode interfaces.
> On Tue, Jul 8, 2008 at 9:46 AM, Joseph Brunner <joe@affirmedsystems.com>
> wrote:
>
>> Where did you read that?
>>
>> even with all sparse-mode interfaces,
> check 224.0..1.40 and any other group
>> with no rp...
>>
>
>> -----Original
> Message-----
>> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
> Behalf Of
>> Harindha Fernando
>> Sent: Tuesday, July 08, 2008 2:39 AM
>> To:
> John
>> Cc: Learn Cisco; ccielab@groupstudy.com
>> Subject: Re: Multicast
> Features
>> Hi,
>>
>> If you have configured all the interfaces to PIM-SM then
> fallback mode will
>> be sparse , if you have at least one interface with
> SM-DM then
>> fallback mode will be Dense, by putting no ip pim
> dm-fallback
>> guaranties that fallback will be in Sparse mode.
>>
>> Rgds,
>>
> Harri
>> On Tue, Jul 8, 2008 at 3:31 AM, John <jgarrison1@austin.rr.com>
> wrote:
>>> spt-threshhold is for source tree. The default is 0 kbs, which
> means
>> that
>>> anything over 0 kbs will go to a source tree. no ip pim-dm
> fallback is
>> to
>>> prevent, at least sparse-dense mode from falling back to
> dense mode for
>>> unknown groups. In the docs I've seen it used in sparse
> mode and
>> sometimes
>>> not. I'm still trying to find a definitive answer on
> that. Ill probably
>>> end up labbing it on friday and then I'll know for
> sure.
>>>
>>>
>>> "The mind is like a parachute it works best when it's
> open"
>>> ----- Original Message ----- From: "Learn Cisco"
> <cisco.learn@yahoo.com>
>>> To: <ccielab@groupstudy.com>
>>> Cc:
> <cisco.learn@yahoo.com>
>>> Sent: Monday, July 07, 2008 5:27 PM
>>> Subject:
> Multicast Features
>>>
>>>
>>> hi, i'm trying to get a better grasp on
> multicast topics. any feedback
>> to
>>>> the following questions would be
> much appreciated:
>>>> 1.) was wondering if anyone can help differentiate
> between the use of
>> "ip
>>>> pim spt-threshold infinity" and "no ip pim
> dm-fallback". they both seem
>> to
>>>> prevent sparse-dense-mode and/or
> sparse-mode pim from reverting back to
>> a
>>>> sourced-tree / shortest-path
> tree unless I'm missing something.
>>>> 2.) would "ip pim accept-rp
> auto-rp" be needed along with one of the
>> cmds
>>>> above to ensure no spt
> paths form?
>>>> 3..) when would "ip pim accept-rp x.x.x.x x" be used? i
> guess if i get a
>>>> question/requirement that states to have a device accept
> join/prune
>> messages
>>>> for an rp i'd know to use this feature, but it
> seems as though their
>> might
>>>> be more to this thing???
>>>>
>>>> 4.) "ip
> pim autorp listener" is the feature to use when desiring to use
> sparse-mode along with auto-rp, right? (without statically assigning
>> the
>>
> rp
>>>> mapping on all sparse-mode devices)
>>>>
>>>> thanks in advance for
> any input,
>>>>
>>>>
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