For intra/inter-as option B, the root is not visible on the leaf. LDP is responsible for building the recursive FEC and signaling the FEC to ABR/ASBR on the leaf. ABR/ASBR must have the PMSI AD router to re-build the FEC (recursive or basic) depending on whether they are connected to another ABR/ASBR or root node. As such, LDP must import the MVPN PMSI AD routes. To save resources, importing MVPN PMSI AD routes are performed manually by the operator using configuration commands. When mvpn-no-export-community command is enabled, LDP requests BGP to provide the LDP task with all the MVPN PMSI AD routes and LDP internally caches these routes. If this knob is disabled and to save resources, MVPN discards the catch routes.
In a scenario where a node running an older image that does not support the mvpn-no-export-community command and that node upgrades to a new image that does support the mvpn-no-export-community command, and if the older image had an inter-as MVPN configuration, then after the upgrade to the newer image, the mvpn-no-export-community command is enabled by default, to ensure a smooth upgrade. This is to make certain that all the routes are imported to mLDP so the inter-as functionality works after the upgrade.
In addition, SR OS supports two major upgrades to enable the MVPN command if an upgrade to a load supporting this knob.