Layer 3 forwarding is all the same. Whitebox stuff generally comes with simple routing protocol implementations.
Cisco, Juniper, et al. have routing protocol implementations generally guaranteed to work with their other network elements. That's how the L3 forwarding tables get populated.
Whether that makes a difference depends on the network architecture. FAANG companies and others are deploying whitebox switches, building "underlay" networks using eBGP, and using SDN as an overlay basically obviating the need to have much intelligence built into the network element.
Cumulus Linux replicates these efforts to some extent. One gets a whitebox switch running Linux with open source routing protocol implementations and configuration via something like ansible.
Yep, and SDN is also possible if you get switches that support things like being an openvswitch-slave or OpenFlow/NetFlow/whateverflow switch. You basically replace the control plane.
That's why a lot of engineering is based around getting data planes working, and ignoring most of the control plane that runs on the application processor. Even if you only get that to control the ASICs and run a simple REST server to accept data plane control commands it's already enough to turn a switch into something useful forever.
