A newly deployed router, without any configured interfaces, has an empty routing table, as shown in the figure.
Before the interface state is considered up/up and added to the IPv4 routing table, the interface must:
- Be assigned a valid IPv4 or IPv6 address
- Be activated with the no shutdown command
- Receive a carrier signal from another device (router, switch, host, etc.)
When the interface is up, the network of that interface is added to the routing table as a directly connected network.