Cisco CCDE v3.0 | CCDE 400-007 Question # 25 Topic 3 Discussion

D (Route maps with tags): When redistributing between OSPF domains at multiple locations (mutual redistribution), route tagging is a key technique to prevent routing loops. Each ASBR applies route tags on incoming routes, and redistribution policies check these tags to prevent re-advertising routes that originated from the other domain.

Other options explained:

A: Virtual links are for connecting discontiguous OSPF areas, not preventing redistribution loops.

B: Router ID uniqueness is required but does not prevent loops.

C: External type 2 redistribution doesn't inherently prevent loops.