Clarification on OSPF RFC2328

Hi, I need a small clarification on Router LSA discussed in RFC2328(Section

Ia Ib Ra----------------Rb

1. Ra and Rb are OSPF routers connected over point to point links.
2. Ia and Ib are the interfaces ip addresses of each of the routers. The interfaces are unnumbered and are assigned ip addresses with a netmask of 32.

Question:

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a. A link of type point-to-point with Link ID set to Rb and LinkData set to Ia. b. A link of type stub network with LinkID set to Ib and LinkData set to 255.255.255.255.

This is assuming that we are following the option 1 for stub networks.

Question 1: Shouldnt we advertise the interface Ia in the router LSA of Ra with a cost of 0? I am unable to find any indication about that from the RFC.

calculation of cost if there are 3 nodes. Or am I missing something??

Question2: The RFC2328 talks about two options for router LSA stub networks. Is there any restrictions on their use? If we have a mix of routers advertising router LSA containing stub networks with option 1 and option 2 in the network, how will they interoperate?

Any help regarding this will be greatly appriciated.. Regards, Robin