Doesn't OSPF Have Auto Summarization?

Question

I asked AI if there is a command in OSPF for auto summarization like RIP and EIGRP. Here is the answer:

"No, OSPF does not have a command like RIP and EIGRP that enables or disables automatic summarization. OSPF does not support automatic summarization at all. You have to configure OSPF summarization manually on each ABR or ASBR where you want to summarize routes. This gives you more control and flexibility over OSPF summarization, but it also requires more planning and configuration."

Even in RIP or EIGRP, I remember it is not recommended to use it.

Why doesn't auto summarization exist in OSPF? And why is it a good idea to disable it in RIP or EIGRP?

I noticed AI said:

This gives you more control and flexibility over OSPF summarization

but is this enough reason? I feel there are more convincing reasons.

I looked for the answer on the Internet for days, but the subject is barely covered, it is not focused on, or too advanced for me to understand.

Answer 1

I'm not going to get into the specifics of the various protocols other than OSPF because it is a good example to start with and it gets confusing if you pull in completely different things. Details vary with other protocols but OSPF is an IGP-Interior Gateway Protocol. That means it is basically meant for exchanging route information within a single organization (an Autonomous System) so default summarization would be of relatively small value because an administrator of a single organization should be able to build their network to make it efficient regardless of summarization and because summarization might result in overly aggressive simplification of route entries.

However, OSPF does support summarization. Asking AI anything is likely to get you limited or wrong information. OSPF summarization is only supported at the Area boundary (between Area Border Routers) since that is the only place where route information can effectively be summarized. Within an Area in OSPF you want detailed route information for improved efficiency and reachability of all networks.

Summarization between Area boundaries makes good sense (if your network design fits it well) since connection from one Area to another implies a boundary of logical network design and therefor route table information as well. Generally all of a logical segment of a network in one Area can be summarized into relatively simple route information when intersecting with another Area and vice versa.

You do need to be careful not to enable summarization when your network design is not cleanly done because you might make some networks unreachable or improperly routed via a configuration mistake. In other words, you have to know what you are doing before trusting it to simplify things without your direct input.

Skip the AI stuff and read the real information.

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html#anc26