An emergency-management office redistributes library prefixes into the core and wants those routes marked so later filters can recognize them. Which route-map action best tags the redistributed prefixes for that policy?
Select an answer to reveal the explanation.
Short Explanation
Tags are sticky notes on routes. You use a redistribute route-map with set tag to stamp the library prefixes, so later filters can keep or drop them without guessing by prefix alone.
Full Explanation
Route tags are numeric labels stored with routes so later policy can recognize a set of prefixes without re-matching every address. When an emergency-management office redistributes library prefixes into the core and wants those routes marked for later filters, the correct tool is a redistribute route-map that includes set tag <value> on the matched clauses. Downstream distribute-lists, route-maps, or redistribution policies can then match tag and permit or deny those library routes consistently across OSPF, EIGRP, or other domains that honor tags.
The interface-only match action, without any set clause, only selects routes and applies no durable mark for later recognition. The set local-preference-only action is a BGP attribute; it does not tag IGP routes system-wide and is meaningless on pure IGP redistribution into OSPF or EIGRP. The set community action on OSPF internals is likewise a BGP community action; OSPF internals do not carry BGP communities for EIGRP neighbors to honor. Communities and tags are different policy currencies.
Exam caveat: tag values are locally significant decimal integers; pick a documented municipal tagging scheme (for example 100 = library, 200 = guest) and apply the same match tag elsewhere. Tags do not replace filters by themselves—you must also deny or accept based on the tag at the control point. Some platforms show tags in show ip route detail or protocol-specific topology outputs; confirm visibility for the protocols you run.
Operational check: after redistribution, show ip route <library-prefix> (with detail where supported) or the EIGRP/OSPF external descriptors and verify the configured tag is present. On a core filter router, temporarily match tag and deny, then confirm the library prefixes disappear from the outbound advertisement while untagged civic prefixes continue. show route-map and show run | section redistribute document the set tag action.