Given FS limite indication, you can mix and match with RPF unicast check and RTBH.
If it's a DoS or small source set DDoS, you use FS. If it's a massive DDoS (thousand of sources), it's better to RBTH, whose limit is route table size (way mooore), an...
You cannot create L3 routing protocol adjacencies on vPC. This is a well-known restriction for vPC design. You have either to use regular PtP links with routing protocol on each of the Nexus boxes (1 PtP to Nexus#1, and another PtP to Nexus#2), with ...
Actually on the open-source part, ExaBGP should work as a flowspec enabled speaker (only on control-plane part, ExaBGP would not interact with dataplane since it's a pure control-plane technology).Given ExaBGP flexibility it would not be that hard to...