Solution to route flapping when routes are imported to each othe

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When static routes, OSPF routes, and IS-IS routes are imported to each other, the source route will be changed because the priority of each routing protocol is different.
Solution: Frequent route flapping consumes much bandwidth and CPU resources and even seriously affects the normal operation of a network. When routing protocols import routes from each other, exercise caution. In particular, when multiple routing protocol import routes from each other, route flapping or even loop easily occurs.
For details, see Route Flapping Occurs When Multiple Routing Protocols Import Routes from Each Other on AR Routers.

Other related questions:
Routing blackhole occurs when OSPF and IS-IS import routes from each other
When OSPF and IS-IS import routes to each other, packets cannot be forwarded based on routes due to the sequence of configuration operations and route convergence. To solve the problem, perform the following operations: 1.When routes of routing protocols are distributed, filter imported routes to prevent loops. 2. When routes of routing protocols are imported, the route priority changes. Notice the route selection change due to imported routes and take measures to control routes. For details, see Routing Blackhole Occurs When OSPF and IS-IS Import Routes From Each Other.

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.

Problem and solution when routes with the same network address but different masks cannot be imported in OSPF on the USG
The reason that routes with the same network address but different masks cannot be imported in OSPF on the USG is as follows; VRP3.0-based products do not support the features defined in RFC2328 Appendix E. Because VRP3.0 uses a network address as an LS identifier, only the first route among the routes with the same network address can be imported to OSPF.

Can OSPF import IBGP routes
In V200R001C00, open shortest path first (OSPF) cannot import Internal Border Gateway Protocol (IBGP) routes. Starting from V200R001C01, the OSPF protocol can import IBGP routes. By default, the OSPF protocol does not import IBGP routes. However, OSPF can import IBGP routes on Multi-VPN-Instance CE (MCE) devices. You can run the vpn-instance-capability simple command for OSPF processes to disable route loop detection and directly calculate routes.

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