Hello,
It looks like You are missing basics here and I thoroughly recommend this book to understand OSPF:
https://www.amazon.com/OSPF-Choosing-Large-Scale-Networks/dp/0321168798
Chris2 wrote:
My big question now is trying to understand why a route will choose area 300 instead of area 0 when there has been no declaration for the route to be in any area.
If You let me know what do You mean saying "declaration(s)" I hope I will be able to answer. OSPF RFC do not have this language. OSPF route is normally "originated" in a given area and then it is propagated into all or none or selected areas.
Where the originated route can be propagated depends on its "Type" (see Jeff Doyle book, or RFC 2328).
Chris2 wrote:As i understand it, a direct interface route would be in the router LSA and advertised across both area 0 and area 300, so why is area 300 chosen?
If direct interface LAN1 is present in area 300 and is injected into OSPF as "passive" then when an Area Border Router (ABR) that has ports in both area 0 _AND_ area 300 will choose area 300 path for an incoming packet whose dst.IP==${IP_from_LAN1_subnet}.
Did it answer You question?
Chris2 wrote:
if i undretsand this correctly, is it impossible to designate a route in an area and maintain tagging? we must just let the protocol advertise to all areas and make its own a choice, which we are unable to influence, to which ospf area it will decide to route across if we ant to tag?
I already mentioned that only Type-5 and Type-7 OSPF LSA/routes can have tags. To inject a subnet as Type-5/7 LSA into OSPF, you need OSPF export policy matching on Your chosen prefix. But then You cannot filter where Type-5 goes since it has AS-wide flooding scope (except stub/NSSA areas) and can be filtered only on ASBR/at point of origination which defeats Your purpose. Type-7 are converted into Type5 by NSSA ABR so same principle applies.
Hope this makes sense.
HTH
Thx
Alex