The VSR-NRC supports originating routes on behalf of the NRC-P toward route reflectors or BGP routers in the network. One of the most common applications is origination using BGP of SR policy candidate paths. The VSR-NRC ROM implements this capability. SR policy candidate paths are advertised as sr-policy-ipv4 BGP routes.
NRC-P sends SR policy candidate path routes to both the active and secondary backup VSR-NRCs using the cproto ROM channel. NRC-P tracks the last route sent to each VSR-NRC separately. This tracking includes whether the last route was route ADD, DELETE, or MODIFY.
The VSR-NRC uses a cache to store SR policy route origination requests from the NRC-P. Upon receiving an SR policy route origination request, the VSR-NRC submits the SR policy route ADD or DELETE to the SR policy manager. ROM handles route ADD as a route MODIFY when there is already a record of the policy candidate path in its cache. The interface from ROM to the SR policy manager database uses <color, endpoint, headend> as the key in the lookup to identify the SR policy and uses <preference, rd> as a parameter to identify a specific candidate path of the SR policy.
The SR policy manager in VSR-NRC saves and organizes all submitted SR policy routes according to owner. Owner STATIC is used for routes submitted using the CLI and the management interface, owner BGP is used for routes submitted using the BGP control plane, and owner NSP is used for routes submitted by ROM.
When a cproto ROM channel goes down, ROM starts a timer with a value equal to the cproto keep alive expiry timeout value of 60 × 2.2 seconds. When this timer expires, ROM scans through all NSP owner records in its route cache and requests the SR policy manager database to flush them. As a result, the BGP module is called upon to withdraw the corresponding NLRIs from the BGP peers in the network.
Because NRC-P switches to the backup VSR-NRC when the cproto ROM channel goes down, the flush operation is necessary. However, if the originally active VSR-NRC is still up, it may remain the preferred source for the routes selected by the BGP peer routers in the network while its own SR policy manager routes are out-of-date with those of the NRC-P.
The NRC-P also supports sending an explicit flush request while the cproto ROM channel is up. This is used to clear stale route entries caused by multiple redundancy switchover operations.
When a cproto ROM channel comes back up, ROM in VSR-NRC sends a Notify message to NRC-P to indicate that the route cache and SR policy manager database were flushed. Subsequently, NRC-P checks the VSR-NRC uptime. If it is lower than the downtime of the cproto ROM channel to the VSR-NRC, NRC-P assumes the VSR-NRC rebooted and sends the full SR policy route database to ROM (full synchronization). If the VSR-NRC uptime is higher than the downtime of the cproto ROM channel to the VSR-NRC, NRC-P sends only the newer records (partial synchronization).