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00:00 Intro
00:56 Theory
05:07 Lab Time!
16:18 Outro
#ccna #ccnp #ccie
OSPF is a link-state routing protocol that creates and keeps neighbor relationships by sharing routing updates with other OSPF routers. Hello packets enable dynamic neighbor discovery and maintain neighbor connections. The passive interface command is used to stop OSPF hello packets or messages on a specified interface. Other routing protocols like RIP and EIGRP use passive interface as well.
Enabling passive interfaces in our network devices mean that:
OSPF continues to advertise the interface’s connected network.
OSPF routers no longer send OSPF Hellos on the interface.
On the interface, OSPF no longer processes any received Hellos.
Why Do We Need OSPF Passive Interface?
The passive interface should be configured on interfaces that do not have an OSPF router connected to them so that they won’t receive any OSPF information. By stopping routing announcements on network interfaces, we tell the router to “participate in OSPF but don't send hello's.” The CPU load of a router can be reduced when using passive interface. This is helpful when routers have 100's of interfaces.
If you are certain an OSPF adjacency isn't needed or expected on a particular interface, then passive interface should be used.
Another reason to use passive interface is security. A hacker could start software that speaks OSPF and could send and reply to hello packets in an attempt to become neighbors. The hacker could obtain important info about the network, inject bogus routes and wreak havoc in the network.
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Configuration used in this video
Specifying an individual interface like g0/1 to be passive
router ospf 1
passive-interface GigabitEthernet0/1
Making all interfaces passive then manually removing it from certain interfaces. Useful when a large amount of interfaces aren't expecting OSPF neighbors to form.
router ospf 1
passive-interface default
no passive-interface GigabitEthernet0/0