Why imported external routes are not displayed in the LSDB on an S series switch

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Perform the following operations on the S series switch to solve the problem.
Run the display ospf interface command to check whether the interface that imports external routes is in the Up state.
Run the display ospf brief command to check whether the device that imports external routes belongs to the stub area.
Check whether the neighbor status is Full if external routes are learned from a neighbor.
Check whether the lsdb-overflow-limit command is configured, and whether the total number of external routes exceeds the maximum limit.
Check whether the asbr-summary command is configured to aggregate external routes.

Other related questions:
Why does not an LSDB display redistributed external routes
Perform the following steps to solve this problem: Run the display ospf interface command to check whether the interface on which external routes are redistributed is in the Up state. Run the display ospf brief command to check whether the router that redistributes external routes belongs to a stub area. Check whether the external routes are learnt from neighbors and whether the neighbor relationship is in the Full state. Check whether the lsdb-overflow-limit parameter is configured and whether the total number of external routes redistributed exceeds the configured upper limit. Check whether the asbr-summary command is configured to summarize external routes.

Precedence of external routes imported by OSPF on S series switches
When an S series switch runs OSPF, you can run the import-route command in the OSPF process view to import external routes. The routes imported using this method are OSPF ASE routes and default precedence is 150.

Why cannot an OSPF route contained in the LSDB/LSA be queried in the routing table on an S series switch
Question: Why cannot an OSPF route contained in the LSDB/LSA be queried in the routing table? Answer: Perform the following operations on the S series switch to solve the problem. Check whether the IP address is valid. Check whether the forwarding address is known and reachable. Check whether the route aggregation or route import is correct. Check whether a different mask or IP address is used in P2P connection. Check whether the advertise route list is configured. Check whether the connection with the backbone area is proper. Check whether OSPF is enabled on the secondary IP address instead of the primary IP address.

Why cannot OSPF on S series switches import BGP routes
Question: Why cannot OSPF import BGP routes? Answer: As defined in RFC 1364, routes learned via IBGP must not be imported into OSPF. That is, OSPF cannot import IBGP routes. PEs can import IBGP routes. Most VPNv4 routing tables contain BGP routes, but the routes cannot be imported into OSPF processes. This is because the vpn-instance-capability simple command is configured in the OSPF processes. After the command is configured, the PE role is disabled on a device and the device acts as an MCE. To enable the PE role on a device, run the undo vpn-instance-capability command.

Routes imported into IS-IS are invalid on S series switches
Q: Why are routes imported into IS-IS invalid? A: For S series switches supporting IS-IS, if the IS-IS level is not set when routes are imported into IS-IS, level-2 IS-IS is used by default. That is, routes are imported into level-2 IS-IS. To import routes to areas of other levels, specify the area level.

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