can't ping the WAN IP of a router

Question

I learned to use cisco packet tracer and found something confusing but actually this is not about the cisco packet tracer . I'm curious if this apply in real network as well.

So i tried building this simple lan setup :

PC 192.168.1.10 ---> switch ---->  router A (192.168.1.1 / 10.0.0.5) ------> router B (10.0.0.4)

The router A has LAN IP 192.168.1.1 and WAN IP 10.0.0.5

In my setup :

PC IP is 192.168.1.10/24 and set gateway to 192.168.1.1

i can ping from PC to 192.168.1.1 (LAN IP of router A) 

i can ping from PC to  10.0.0.5 (WAN IP or router A)

The problem is : if i disconnect router B from router A , i no longer can ping to 10.0.0.5 . Why is it ? why it depends on the connection of router B while that IP (10.0.0.5) has nothing to do with router B

If i reconnect again router A and B, then i now can ping from PC to 10.0.05

How does it actually works ?

Thanks

Answer 1

If Router B is disconnected, the interface on Router A goes down because there is no connection. When an interface is down, it has no address, so the address is withdrawn from any routing tables.

You could do something like put a switch between the routers. When Router B is disconnected, Router A would still have a connection on that interface, and the interface would remain up.