passive-interface — router
Disables a routing protocol on a specific interface either partially (RIP, IGRP) or completely (EIGRP, OSPF, etc.)
For RIP and IGRP, this command causes the specified
interface to listen for routing updates but prevents it from sending them. For OSPF, EIGRP, or other “hello-based” routing protocols, this command effectively disables the protocol on that interface (both sending and receiving). These protocols cannot operate without exchanging hello messages.
router igrp 100 network 10.0.0.0 ! Suppress routing advertisements on serial 1 passive-interface serial 1