Cisco
400-007 · Question #446
400-007 Question #446: Real Exam Question with Answer & Explanation
The correct answer is C: Enable route-filtering on OSPF backbone routers for spoke traffic.. Filtering spoke prefixes on the temporary OSPF backbone between HUB A and HUB B prevents those routes from circulating simultaneously via OSPF and the new eBGP/L3VPN path, removing dual-path feedback and avoiding routing loops during the phased migration.
Question
Refer to the exhibit. A customer network design team is planning a migration from a legacy TDM- based L2VPN to an MPLS-based L3VPN. Migration is planned in a phased approach: - OSPF backbone Link between HUB A and HUB B sites to be migrated to eBGP. - Spoke A2 and Spoke B1 will be migrated to the L3VPN. Which solution design can be considered to avoid routing loops during backbone link migration?
Exhibit
Options
- ARedistribute EIGRP 200 and 300 with low cost into BGP.
- BOSPF backbone area advertises summarized routes to hub.
- CEnable route-filtering on OSPF backbone routers for spoke traffic.
- DAdvertise low AD value for transit traffic on hub sites.
Explanation
Filtering spoke prefixes on the temporary OSPF backbone between HUB A and HUB B prevents those routes from circulating simultaneously via OSPF and the new eBGP/L3VPN path, removing dual-path feedback and avoiding routing loops during the phased migration.
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