Leaf not support Multicast

[apache_le]

I have a design issue where the Leaf is not an -EX version so it doesn't not support Multicast routing.  I have Bridge Domain in this Leaf that need to receive Multicast traffic.  So according to Cisco documentation, I need to have an external router to perform PIM.  So does that mean the SVI for this particular BD or Vlan will be on the router itself, not inside the fabric?  Is there any documentation on this design?  thanks.

[Jenny Ngo · Accepted solution]

As per your TAC case, we went over that in a hybrid non-EX and -EX leaf switch fabric, the best practice would be to use an external router to perform multicast routing.

http://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-737592.html

Your default gateway would reside on the external router and you will need to make sure IGMP snooping is enabled in your fabric.

This Cisco Live presentation has some information about the design/configuration of the multicast routing via an external router (see ACI and IP Multicast section):

https://www.ciscolive.com/online/connect/sessionDetail.ww?SESSION_ID=89910&tclass=popup

[apache_le]

"Your default gateway would reside on the external router"   

I would like to challenge the above statement as my initial thought that's not the case.  And in the Cisco Live presentation, the presenter mentioned all of the default gateways will reside inside the fabric.  When he shows the configs of the external PIM router, I notice he used "x.x.x.253" and "x.x.x.254" as the IP address of the L3 sub-interfaces.  So I suspect "x.x.x.1" reside inside the fabric. My conclusion is that the external PIM router only need to have a L3 connection into the BD with multicast requirement.  

[Joseph Ristaino]

The limitation is where the Multicast Routing will happen.  Without EX Switches, we cannot enable PIM on BD's and L3Out's so the BD Subnet cannot be the Gateway AND Do Multicast Routing.

By having the PIM router plugged into the fabric, we will snoop IGMP and forward all multicast traffic in that BD towards the router.  We don't have the ability to advertise MCAST Routes via PIM to Border Leafs or external Routers without the New hardware.

Default Gateway should only come into play for Unicast Traffic.  So having the DG in the fabric with a PIM router advertising IGMP for certain groups I don't think should cause any issues, but we would need to test it.  I'm not aware that this is currently "unsupported".

[apache_le]

Hi Joseph,

So having the DG inside the fabric for unicast routing and external PIM router plugged into the fabric will also work for both Unicast and Multicast?  The reason I want to have the DG inside the fabric is to avoid traffic between BD not having to go out to the PIM router then hairpin back to the fabric for inter-BD communication with extra hop.