Let's break it down step by step based on Huawei's routing protocol behavior:
R1imports thedirect route 10.1.1.0/24intoOSPF.
This route is advertised byR1 to R2 and R3viaOSPF.
BothR2 and R3are runningIS-IS, andbidirectional route redistributionis configured between OSPF and IS-IS.
R2 and R3 bothre-advertisethe OSPF-learned route into IS-IS and then potentiallyre-learnit back from the IS-IS domain, causingredistribution loopsunless properly controlled.
Now, the question focuses onR3’s routing table:
R3 already learns the routedirectly via OSPFfrom R1.
It also learns the same route again viaIS-ISfrom R2 (looped back due to bidirectional redistribution).
Reference from Huawei HCIP-Datacom-Core Technology Study Guide:
“OSPF ASE routes are assigned a default preference of 150. If a route is redistributed from another protocol (like IS-IS) into OSPF, and then re-learned, it is considered an ASE route.”(Chapter: OSPF Advanced Features – Section: Route Redistribution Behavior)
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