Why does the point-to-multipoint OSPF network type generate the /32 routes and how can I stop them from being advertised?
The behavior of point-to-multipoint is to advertise each end-point out as a /32 and suppress the advertisement of the network itself. Point-to-multipoint advertises the end points to overcome possible reachability issues between devices that are on the same logical subnet but do not have direct communication (i.e. spoke to spoke communication in a hub and spoke environment). The OSPF point-to-multipoint and loopback network types do not advertise the network itself but advertise a host route for each end-point. This is as per the RFC.
If you want to suppress the /32s and advertise only the network, you would need to use an OSPF network type other than point-to-multipoint or configure the network to be in its own OSPF area. After the network is put in its own OSPF area, use the area range command to summarize the /32s so other routers only see the summarized route.
About Brian Dennis, CCIE #2210:
Brian Dennis has been in the networking industry for more than 22 years, with a focus on Cisco networking for the past 16 years. Brian achieved his first CCIE in Routing & Switching in 1996, and is currently the only ten year CCIE that holds five CCIE certifications. Prior to working with INE, Brian taught and developed CCIE preparation courses for various well known training organizations. Brian not only brings his years of teaching experience to the classroom, but also years of real world enterprise and service provider experience.
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