Question

A network engineer migrates R1 from EIGRP classic mode to EIGRP named mode. After the migration, R1 forms a stable adjacency with R2 (still in classic mode) but the neighbor relationship with R3 (also classic mode) repeatedly flaps with the log message '%DUAL-5-NBRCHANGE: ... K-value mismatch'. On R1 named mode, the engineer configured 'metric weights 0 1 1 0 0 0 0' under the address-family topology base. R2 and R3 both use default K-values except R3, which was previously configured with 'metric weights 0 1 0 0 0 0 0'. What is the root cause of the flapping adjacency between R1 and R3?

Accepted Answer

R1's named-mode K-values (K1=1, K3=1) do not match R3's classic-mode K-values (K1=1, K3=0), and EIGRP requires K-values to match for an adjacency to remain up.

Answer

Named-mode EIGRP is incompatible with classic-mode EIGRP, so R1 cannot form any stable neighbor relationships with classic routers.

Answer

The autonomous system numbers differ because named mode uses a different AS numbering scheme than classic mode.

Answer

R1 and R3 have mismatched hello and hold timers introduced by the named-mode migration defaults.