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The NIM (network interface manager) microservice is already testing the connectivity towards the controller, and is also detecting when complete local connectivity is lost (the cable being unplugged and/or the DHCP lease expiring). The result pf that That checking and testing results in updates to the DeviceNetworkStatus `DeviceNetworkStatus` object. That testing mechanism will be extended to test all of the management ports, and report the lastSucceeded/lastFailed timestamps in the DeviceNetworkStatus `DeviceNetworkStatus` per each port.
The zedrouter microservice (which implements the network instances) will observe these changes and use it them to update the network instance's use of the port, and the associated NAT rules (MASQUERADE and port map rules) to be associated with the currently used management port. Also, the PBR rules for the source IP address of the network instance (shown in ip rule show) will be updated to refer to the table associated with the currently used management port.
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These policy and priority handling enhancements will be explored in more detail.
Implementation notes (order of deliverables):
1) NIM should produce NITS (Network Instance Test Status) based on IP being available on ports. NIM should also respond to any changes to ports/IP addresses (UP/DOWN/Address change) and pick one from the ports available to network instance. In this phase, NIM only checks if there is an IP address assigned to port and would deem it usable if it does have one assigned. NITS status should have network instance and the port name that should be used for sending out traffic.
Zedrouter should then respond to NITS and re-configure/program NAT rules, port map rules etc corresponding to applications attached to the network instance.
2) Enhance NITS test to use Zedcloud ping to find any remote network failures.
3) Assign priorities to ports and produce NITS results based on priorities. Free port flag that is present currently will be replaced with priority relative to other ports. NITS should give the highest priority working port for a given network instance.
4) Network instances should allow user to configure a test target URL/IP address along with test timer interval. EVE device instead of using the default Zedcloud ping, will use the configured test URL/IP to test if a given port can be used.