In EIGRP the passive-interface command stops sending outgoing hello packets, hence the router can not form any neighbor relationship via the passive interface. This behavior stops both outgoing and incoming routing updates.
Config:
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R3# sh ip int br
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 23.23.23.2 YES manual up up
FastEthernet0/1 unassigned YES unset administratively down down
Loopback0 100.100.100.100 YES manual up up
Loopback1 110.110.110.110 YES manual up up
Loopback2 120.120.120.120 YES manual up up
R2#sh ip int br
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 23.23.23.1 YES manual up up
FastEthernet0/1 unassigned YES unset administratively down down
Loopback0 10.10.10.10 YES manual up up
Loopback1 11.11.11.11 YES manual up up
Loopback2 22.22.22.22 YES manual up up
Loopback3 33.33.33.33 YES manual up up
We have loopback interfaces on R3 and R2 to make it look like we have networks connected to the routers. We also disable auto summarization on both R2 and R3 to make it look like the loopback interfaces are connected to the bove networks.
Now we make fa0/0 on R2 passive interface and capture the traffic on fa0/0 on R3.
R2(config)#router eigrp 1
R2(config-router)#passive-interface fa0/0
R2(config-router)#
*Mar 1 02:27:15.183: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 23.23.23.2 (FastEthernet0/0) is down: interface passive
R2(config-router)#^Z
R2#
Here is the output from the wireshark:
You will notice that as soon as we make fa0/0 on R2 a passive interface it stops sending hello packets.
The adjecency drops immediately. It doesn't wait for hold time to expire.
