Which method should you use to block all routing updates from being sent into a network through an interface?
- Static route
- Default route
- Passive interface
- Route-update filtering
To stop all outbound routing updates from an interface, you can use the passive-interface command. The effect of the passive-interface command is dependent on the routing protocol running on the interface. For EIGRP, the router will not only stop sending routing updates, but also hellos, which means that it will not form a neighbor relationship with another EIGRP router on that interface. This is also the case with OSPF and IS-IS. With RIP, however, the router will continue to send hellos even as it stops sending routing updates and it will still receive routing updates.
There are numerous reasons to use the passive-interface command. For instance, suppose that you have a LAN with only end hosts on it and no other router. Additionally, there is no reason to send EIGRP packets, but you want EIGRP to advertise that the network can be reached. The combination of a network statement for that interface plus a passive-interface command would be appropriate.
Route-update filtering can block all routing updates if you prefer, but it is really intended for selective filtering of updates. If your goal is to block all updates, the passive-interface command is best.
Default routes and static routes can be used as ways around having to send routing updates out an interface. However, if your goal is to block updates, you should issue the passive-interface command.
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