In a EIGRP network, how do you advertise a default route to all the routers?  

With EIGRP,  there are a few ways to advertise a default route to the rest of the network.

 1. Create a static route on the border router (of the EIGRP domain) and
    redistribute it into EIGRP.
 2. Create a summary route (0.0.0.0) on the border router.
 3. Use the `default-network` command on the border router to generate a default route.

The 2nd and 3rd techniques will give you the output you've shown.

`default-network` is a hold over from classful routing and is rarely used anymore.

Cisco has some good explanations [here][1]  and [here][2].

 


  [1]: https://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/16448-default.html
  [2]: http://cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/200279-Configure-Default-route-in-EIGRP.html