What is null interface in a Cisco Router?
A null interface like a loopback interface is a logical interface which is always up. This interface is different from the physical interfaces i.e. Ethernet or Gigabit Ethernet interfaces.
Unlike other interfaces the null interface does not receive or send traffic, thus any traffic going towards the null interface will be dropped.
Null interface will take in or absorb the traffic or packets that are coming and will not forward these to another destination or interfaces.
Since the IP datagram or packet that is received by the null interface is dropped, it is also known as bit bucket.
Using null interface helps to avoid routing loops. In EIGRP (Enhanced Interior Gateway Protocol) summarization, a route is created to Null0 interface.
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- Network Topologies