Generally speaking, you would want to use it when some networks within the summary are only reachable through routes with shorter prefix-lengths, e.g. the default-route.
Let's say you summarize 172.16/16 on an ABR for the backbone area but you have some DMZ-networks within that range but outside the OSPF domain which are only reachable through the default-route. Now with a discard-route for 172.16/16 in area 0 pointing to Null0, you would have to add static routes to those DMZ networks or enable a routing-protocol.
In the above example, like you mentiond- if we want to reach 172.16 subnets then we will configure static routes on the ABR but we won't delete the discard route.
what I wanted to point out is that the automatic discard route cuts the reachability to the DMZ-networks (e.g. 172.16.100.0/24), which were reached through the default route before the summary was configured. Instead of configuring static routes, you could use the "no discard-route internal" command to solve the connectivity problem.
(The discard-route has a prefix-length of /16 which is longer than the default-route's /0)
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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