Re: Multicast Features

From: Paul Cosgrove (paul.cosgrove@heanet.ie)
Date: Tue Jul 08 2008 - 14:19:26 ART

Doh! Receiving routers "will NOT send the traffic out any other
interface..."

Paul Cosgrove wrote:
> 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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>>
>>
>
> 

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