What does the network command do in EIGRP, and what does passive-interface change?
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The network statement with a wildcard mask selects interfaces. Any interface whose primary address
falls in the range runs EIGRP: it sends hellos and its subnet is advertised. It does not inject a
route the way a BGP network statement does. passive-interface keeps the subnet advertised but stops
hellos, so no neighbor can form there. Use it on user and server LANs.
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Precise network statements
router eigrp 100
network 10.0.12.0 0.0.0.255
network 10.1.0.0 0.0.0.255
passive-interface default
no passive-interface GigabitEthernet0/0/0passive-interface default plus explicit exceptions is the safe pattern: a new LAN interface comes
up passive, so nobody can plug in a router and start exchanging routes.
Checking it
R1# show ip eigrp interfaces
EIGRP-IPv4 Interfaces for AS(100)
Xmit Queue PeerQ Mean Pacing Time Multicast Pending
Interface Peers Un/Reliable Un/Reliable SRTT Un/Reliable Flow Timer Routes
Gi0/0/0 1 0/0 0/0 1 0/0 50 0Passive interfaces do not appear here, but their subnets are still in the topology table and
show ip protocols lists them as passive.
Passive is not the same in every protocol
| Protocol | Passive interface |
|---|---|
| EIGRP | No hellos sent or processed, no neighbors, subnet still advertised |
| OSPF | Same idea: no hellos, subnet still advertised |
| RIP | Stops sending updates, but still listens to received updates |
They will ask next
What does
network 10.0.0.0with no wildcard do?It is taken as the classful network, so every interface in 10.0.0.0/8 runs EIGRP. That is easy to type and easy to regret, because it enables EIGRP on interfaces you did not intend.
Traps
- Thinking the network command decides which prefixes are advertised regardless of interfaces. It matches interfaces only.