IP Default Gateway
This command allows the router to maintain routing functionality when it stops being a router. What that means is that, after a router crashes, it falls back to basic switching functionality. The default-gateway is where the router will send all packets.
Router(config)#ip default-gateway <ip address>
In the below example R1 has lost routing functionality, we will set a default gateway so it can restore reachbility.
R1(config)#do show ip route Default gateway is not set Host Gateway Last Use Total Uses Interface ICMP redirect cache is empty
After we add the default gateway we can now ping R2’s loopback.
R1(config)#do show ip route Default gateway is 10.1.1.2 Host Gateway Last Use Total Uses Interface ICMP redirect cache is empty R1(config)#do ping 18.104.22.168 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 22.214.171.124, timeout is 2 seconds: !!!!!