Exam 400-007 topic 1 question 57 discussion

i would choose C as we have a single ASBR so we want to send summerized route to ASBR before redistribution, https://learningnetwork.cisco.com/s/question/0D53i00000Kt2ysCAB/redistribution-and-summarization-between-ospf-and-eigrp-where-is-best

I would choose C. We could summarize on the ASBR but need to perform config to avoid accidentally leaking anything into OSPF domain. Far more efficient to summarize on the device facing the ASBR, so the ASBR receives the summarized route. Also follows the principal of information hiding according to Optimal Routing Design book.

Summarisation between OSPF and EIGRP has to be done on the ASBR. In OSPF you can summarised on OSPF process no interface. But in EIGRP you can summarise to the level interface.

Summarization can also be performed for external routes, as illustrated in Figure 3-27. Each route that is redistributed into OSPF from other protocols is advertised individually with an external LSA. To reduce the size of the OSPF LSDB, you can configure a summary for external routes. Summarization of external routes can be done on the ASBR for type 5 LSAs (redistributed routes) before injecting them into the OSPF domain. Without summarization, all the redistributed external prefixes from external autonomous systems are passed into the OSPF area. https://www.ciscopress.com/articles/article.asp?p=2294214&seqNum=3

It says to not affect how EIGRP is routing, hence route summarization on the appropriate ASBRs