Hello Andyo,
I have found the sentence here
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/multicast/configuration/guide/n7k_multic_cli_5x/pim.html#96194
with PIM Bidir is referring to the specific PIM SM that uses PIM directional (only shared tree is built rooted at the RP and traffic can leave the RP or it can be sent to the RP, from this the name bidirectional).
PIM bidirectional is the best choice for environments with many multicast sources like for example one thousand of IP video cameras.
My understanding is that you can still use conventional PIM SM over VPC.
Only you cannot have a subset of multicast groups processed by PIM Bidirectional.
>> As soon as above is true, enablement of PIM on this link becomes a problem in general, isn't it? :0)
IT is a problem if you would like to use PIM Bidir to save on control plane state memory usage by using PIM Bidir you create only the shared tree rooted at the RP that can be used by source PIM DR to send traffic originated by a multicast source to the RP, or to send traffic downstream to all possible receivers from the RP to all branch and leaf PIM routers with receivers.
The saving on states means that only (*,G) entry for RPT tree is created avoiding to create many (S1,G), (S2,G), ...(Sn, G) mroute entries rooted each at the PIM DR for Sx source.
If you don't have many multicast sources you can use PIM SM with no issues.
I guess you were thinking of BFD support for PIM on the vPC link to ensure fast convergence?
Another limitation is that shared-tree only on last hop mcast router is not supported on vPC
see
>>The Cisco NX-OS software does not support the shared-tree feature on vPCs. For more information about vPCs,
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/multicast/configuration/guide/n7k_multic_cli_5x/pim.html#45763
Hope to help
Giuseppe
