Octavia can use OVN as a provider driver using it's driver framework. The OVN Octavia provider driver, part of ML2/OVN, does not implement all of the functionality of the Octavia API [1]. One feature that should be supported is allowed_cidrs. The Octavia allowed_cidrs functionality allows Octavia to manage and communicate the CIDR blocks allowed to address an Octavia load balancer. Implementing this in the OVN provider driver would allow load balancers to be only accessible from specific CIDR blocks, a requirement for customer security ina number of scenarios. [1] https://docs.openstack.org/octavia/latest/user/feature-classification/index.html#listener-api-features
In ovn-octavia-provider the SGs being applied are the one of the members. So there is no need for using allowed-cidrs to restrict the traffic to the members, this can be done by having the desired security group rules on the members.