Default routes question

[net guru]

Hello experts,

I crossed this question mentioning that in large entreprises , a stub router should be configured with a default route if routing is needed. as am still an academic student I don't really get the thing behind configuring default routes in a existing network.

thank you so much for answering !

[balaji.bandi]

i can give you the command for you straight away to configure.

Since you learning academic, i suggest to read some good document how the routing injects:

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/47869-ospfdb10.html

[net guru]

Thank you for replying Sir ,
Maybe my question wasn't clear enough but I wanted to know the concept/the WHY we do configure a default route.
note: am preparing for the CCENT exam , I still have no in-depth knowledge about OSPF.

[Richard Burts]

The original question was not clear. But your follow up is quite clear:

WHY we do configure a default route

I would suggest that the answer might begin by understanding that the IP routing table of a device (perhaps a router, perhaps a layer 3 switch, perhaps some other device) has entries that provide information about how to reach remote destinations. It may have multiple entries for various networks and subnets that it knows how to access. But what would happen if a packet arrives at the router/switch/etc and the destination is a network/subnet for which we do not have an entry? If the router/switch/etc does not know how to access the destination it would drop the packet. The default route is the answer to that issue. The default route says that if there is a destination for which we do not have specific routing information here is where to go to get there. 

If our router/switch/etc is running a dynamic routing protocol it might learn a default route via that routing protocol. But if the routing protocol does not dynamically learn a default route then we have an option to manually configure the default route as a static route.

HTH

Rick