[c-nsp] MVPN

[Phil Mayers]

Christian Meutes wrote:
> Hi Phil,
> 
>> As far as I can see, SSM would only be of specific help if the >255
>> groups were coming from >1 PE. You'd still have problems with >255 groups
>> on 1 PE using SSM.
> 
> Even then I could use different data-mdt's for every PE in same VRF in
> SM mode or not?
> 
>> The traffic will not flow via the RP, since all the PEs should have
>> joined towards the other PEs for the default or data group in question.
>>
>> The issue is that some traffic might be sent to PEs which have no
>> interest in it (if you have more active MVPN groups than data groups, or
>> if it's flowing in the mdt default) but it will still flow on the source
>> tree in the P-space, not the shared tree.
>>
>> Whether that's actually a problem depends on the bit rate of the traffic,
>> number of PEs and types of links. Not the most helpful answer I'm afraid.
> 
> I just tested it in SM mode. What happens is that no more streams can be
> send because of the exhaustion of all data-mdt's. Switchover to data-mdt
> is configured to 1 and as soon as traffic arrives a data-mdt is tried
> to open and unfortunately fails therefore.

Really? That's got to be a bug. What platform are you on?

> 
> The only solution as far as I can see is to do SSM without a data-mdt.
> Sure I could also use SM without a data-mdt but that would concentrate
> everything on the RP which would be the worst case of all.

You seem to be mis-understanding how PIM-SM works. When a source starts 
up, only the *first few* packets are tunneled via the RP; these few are 
forwarded down the shared tree, which triggers the other PEs to do a 
join to source, and the traffic then flows optimally; the RP will then 
send a Register-Stop to the PE of the source, which stops the tunneling.

> 
> Or do I miss something?
> 
> cheers,
> Christian
> 
> 
>