Data MDT In Case Of Dense Mode

Unanswered Question
Feb 25th, 2009

I am getting a weird issue in MVPN cloud. Our cloud is working on dense mode and I am getting data mdt entires. How this can be possible?

As per understanding data mdt cannot converge until and unless it get the S,G entry. IN case of dense mode we donot have S,G entries. So data mdt convergence is not possible.


shivlu jain

I have this problem too.
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Giuseppe Larosa Wed, 02/25/2009 - 11:41

Hello Shivlu,

are you using

the newer

address-family ipv4 mdt ?

with mdt commands in VRF configuration ?

I wonder if this can cause some changes

Hope to help


Laurent Aubert Wed, 02/25/2009 - 19:13


Are you referring to the customer or the SP multicast domain ?



Harold Ritter Wed, 02/25/2009 - 21:19


Data MDT can be used in SSM mode but this is not an absolute must. It can also be ran in ASM mode, in which case PIM dense mode should work too, although I have never tried it myself. If you want it to be SSM though, you need to make sure SSM is enabled on all routers and that the address range used by the data MDT is covered by SSM.


shivlu jain Wed, 02/25/2009 - 23:16

the main issue is that our core is of dense mode enabled. So no ASM,RP,SSM. Now i am going to migrate dense mode to SSM. But during migration I saw the weird data mdt convergence. As per me if the core is pure dense mode then data mdt cannot be cnverged at any how. I am pasting some outputs.

sh ip pim vrf XYZ mdt receive

Joined MDT-data [group : source] uptime/expires for VRF: XYZ

[ :] 02:50:05/00:02:14

[ :] 05:01:05/00:02:19

With this we are using ipv4 mdt some of the routers.


shivlu jain

Harold Ritter Thu, 02/26/2009 - 07:05


Just for your information, ASM does include PIM dense mode as well. SSM does work in a dense mode context but it is not ideal as the dense mode flooding behavior (every 3 minutes) will apply to the SSM group range as well.

The better solution is definitely to reconfigure all of the interfaces in your core to "ip pim sparse-mode".


shivlu jain Thu, 02/26/2009 - 23:31


The given explicitly states that Data MDT is not supported by SSM.

But in my network how the data mdt is converging although we are using dense mode in the core. Really not able to understand where the problem is?


shivlu jain

Laurent Aubert Fri, 02/27/2009 - 06:24

I think you meant PIM-DM right ?

I said it's not supported not it's not working ;-)

The difference is if you have an issue with this set-up, the first thing TAC will tell you is to migrate to PIM-SM, SSM or Bi-Dir and to re-contact them if you still have the issue.

When customer traffic reach the threshold to switch to Data MDT, the PE connected to the source will send the MDT-Join on the default MDT, wait 3s and then start sending the multicast traffic in the Data MDT.

So even in dense mode, all the remote PEs will receive this traffic but as I said we don't support officially this type of implementation.

I suggest you to move forward and to migrate your core to PIM SSM so you will be safe in term of support.



shivlu jain Mon, 03/02/2009 - 02:10


I have doing the migration from DM to SSM mode. Even opened a case with tac but did not get any fruitful result.


shivlu jain


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