Key learning:
passive-interfaces feature, it's a L3 concept
Issue recap:
There is a pair of routers running EIGRP, what we gonna do is passive all interface except vlan 800, 801. After basical EIGRP routing configuration, below passive-interface was setted.
routerA:
router eigrp 815
passive-interface default
no passive-interface vlan 800
no passive-interface vlan 801
routerB:
router eigrp 815
passive-interface default
no passive-interface g1/2
no passive-interface g1/1
The gigabyte interfaces were access ports belonging to vlan 800/801.
But the EIGRP neighbor can not been built up since in routerB, vlan 800/801 was already passive-interface, no any hello packet sent to neighbor. Actually, passive-interface will not send routing update but receive in general, but it’s different feature at base on different routing protocol. RIP and IGRP inherited the normal definition of passive-interface, but in OSPF and EIGRP, the passive-interface will neither receive nor send the routing update, it make the interface logical down within routing AS.