Comprehensive and Detailed In-Depth Explanation:
1. Understanding the Issue of OSPF Type 5 LSAs in a Dual-Homed CE Scenario
* OSPF Type 5 LSAs (External LSAs) are used in OSPF to advertise external routes, such as those learned via BGP or redistributed from another protocol.
* In a dual-homed CE setup, like the one in the figure, CE2 connects to both PE2 and PE3 using OSPF.
* PE2 and PE3 both redistribute BGP routes into OSPF and advertise them to CE2.
* CE2 then forwards these LSAs between PE2 and PE3, potentially causing a routing loop because each PE may re-learn its own previously advertised routes.
2. How Route Tags Prevent Loops in OSPF-BGP Redistribution
* The route-tag command assigns a tag to redistributed routes.
* When a router receives an external OSPF LSA (Type 5), it checks the route tag.
* If the route tag matches the locally configured tag, the router ignores the route to prevent loops.
Example Configuration on PE Routers:
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PE2:
router ospf 1
import-route bgp 100 route-tag 65001
PE3:
router ospf 1
import-route bgp 100 route-tag 65001
* Both PE2 and PE3 tag their redistributed BGP routes with 65001.
* If PE3 receives an LSA from CE2 with the tag 65001, it ignores it (because it knows it originally advertised it).
# This prevents OSPF from incorrectly preferring a route that was originally sourced from itself, avoiding routing loops.
3. Evaluating the Answer Choices
# TRUE: If the route tag of the received route matches the locally configured tag, the route is ignored, preventing loops.# FALSE: The statement is correct, so False is incorrect.
Thus, the correct answer is: A. TRUE
Final Conclusion:
# The statement is TRUE because route tagging is a valid method to prevent OSPF Type 5 LSA loops in dual-homed scenarios.