- Tagging provides a way to mark common or similar routes to manipulate later.
- In redistribution scenarios with mutual redistribution on two different routers, any routes that gets redistributed from one route process to another are tagged.
- When the other router sees those tags on the route, that route to keep from adding non-optimal routes to its routing table.
- Tags can also be used to do other manipulation such as setting higher metrics or changing ADs.
OSPF
1234567891011121314151617181920 R102#show run...router ospf 1log-adjacency-changesredistribute connected subnets route-map SETTAGnetwork 192.0.2.0 0.0.0.255 area 0!route-map SETTAG permit 100set tag 55555...R101#sh ip route 10.0.0.2Routing entry for 10.0.0.0/24Known via "ospf 1", distance 110, metric 20Tag <strong>55555</strong>, type extern 2, forward metric 10Last update from 192.0.2.102 on Ethernet0/0, 00:00:13 agoRouting Descriptor Blocks:* 192.0.2.102, from 192.0.2.102, 00:00:13 ago, via Ethernet0/0Route metric is 20, traffic share count is 1Route tag <strong>55555</strong>
EIGRP
123456789101112131415161718192021222324 R102#sh run...router eigrp 1network 192.0.2.0redistribute connected route-map SETTAGno auto-summary!route-map SETTAG permit 100set tag 55555...R101#sh ip route 10.0.0.2Routing entry for 10.0.0.0/24Known via "eigrp 1", distance 170, metric 409600Tag <strong>55555</strong>, type externalRedistributing via eigrp 1Last update from 192.0.2.102 on Ethernet0/0, 00:00:14 agoRouting Descriptor Blocks:* 192.0.2.102, from 192.0.2.102, 00:00:14 ago, via Ethernet0/0Route metric is 409600, traffic share count is 1Total delay is 6000 microseconds, minimum bandwidth is 10000 KbitReliability 255/255, minimum MTU 1500 bytesLoading 1/255, Hops 1Route tag <strong>55555</strong>
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Corrections are encouraged.