When I add a default route I am able to ping and I don't know why

[hfakoor222]

here is my topology

There are no routing protocols 

The only static route is 

from ISP server, which allows the ISP server to ping PC2, PC3

ip route 192.168.1.0 255.255.255.0 200.200.100.1

i can ping to the ISP 1 router from the Webserver and that is it

I cannot ping the  Singapore server fromWebserver currently

however when I add a default route at Singapore server

ip route 0.0.0.0 0.0.0.0 200.200.100.2

I AM able to ping PC-3 from Webserver

Can someone explain the logic of adding a default route on Singapore allows me to reach it from Webserver?

Also is there a way I can add a static route on Webserver or ISP1, in place of the default route, to reach the PC's from Webserver?

[David Ruess · Accepted solution]

A couple things here. First off you have 2 routing statements. The original of

ip route 192.168.1.0 255.255.255.0 200.200.100.1 and the default 0.0.0.0 route.

A router needs to know how to GET to a destination and also that destination needs to know how to get BACK to the original router (in the case of a ping anyway)

SO the first route: 

ip route 192.168.1.0 255.255.255.0 200.200.100.1

Says to get to the 192.168.1.0 network go this way -> 200.200.100.1

BUT the 192.168.1.0 network does NOT know how to get back to the 200.200.0.0 networks you have configured since Singapore only knows how to get to the 192.168.1.0 and the 200.200.100.0 network since its directly connected so a ping from 200.200.50.0 network wont wonk since Singapore doesn't "know" about it.

In comes your default route. This tells Singapore "Hey, If you don't know where to send anything...just send it to your next hop of 200.200.100.2...which in turn DOES know how to get to the web server network of 200.200.50.0 network since its directly connected. And that's why the ping works.

Hopefully that clears some things up.