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1.0.- The Opaque LSA  

Opaque LSAs are types 9, 10, and 11 LSAs.  The flooding scope is associated with the type as follows:
  • LSA type 9 are link-local scope; they are not flooded beyond the local (sub) network.
  • LSA type 10 are area-local scope; they are not flooded beyond the borders of their associated area.
  • LSA type 11 are AS scope; they are flooded throughout the entire AS. Their scope are equivalent to the flooding scope of AS-external (type 5) LSAs. Then, they are not flooded into stub areas.
The link-state ID of the Opaque LSA is divided into an Opaque type field (first 8 bits) and a type-specific ID (the remaining 24 bits). Opaque LSAs contain some number of octets of application-specific data padded to 32-bit alignment. The packet format is as follows:

One receiver must always store a valid received Opaque LSA in its LS-database; it must not accept Opaque LSAs that violate the flooding scope (e.g., a type-11 Opaque LSA should not be accepted in a stub area).
Opaque LSA flooding rules
  • Opaque LSA type 9: if the interface where the LSA is received is not the same as the target interface, the LSA must not be flooded out that interface or to that neighbor.
     
  • Opaque LSA type 10: if the interface where the LSA is received is not associated to the same area associated with the LSA (upon reception), the LSA must not be flooded out the interface.
     
  • Opaque LSA type 11: if the interface where the LSA is received is associated with a stub area, the LSA must not be flooded out the interface, must be discarded and must not be acked.
The Options field
The Options Field enables OSPF routers to support (or not support) optional capabilities, and to communicate their capability level to other OSPF routers. The Options Field allows a router to reject a neighbor because of a capacity mismatch or not to forward certain LSAs to a neighbor because of its reduced funcionality.
The six-bit of the Options Field is reserved to indicate Opaque LSA capability (O-bit), as follows:

O-bit
  This bit describes the router's willingness to receive and forward Opaque-LSAs as specified is this document.  
Opaque-capable routers should not flood Opaque LSAs to non-opaque-capable routers. As a general principle, Opaque LSAs are only flooded to those routers that understand them.
An opaque-capable router learns of its neighbor's opaque capability at the beginning of the "Database Exchange Process" by checking the Options Field's O-bit. Later on, Opaque LSAs are only placed on the link-state retransmission lists of opaque-capable neighbors. However, when LSA packets are sent as multicast, a non-opaque-capable router may receive an Opaque LSA. In this case, the router will simply discard the LSA as having unknown LS type.  

Modifications to the Neighbor State Machine
The Neighbor State Machine remains unchanged except as indicated below:
State(s): ExStart  
Event: NegotiationDone  
New state: Exchange  
Action:

 
The router must list the contents of its entire area link-state database in the neighbor Database summary list. The area link-state database consists of the Router LSAs, Network LSAs, Summary LSAs and types 9 and 10 Opaque LSAs contained in the area structure, along with AS External and type-11 Opaque LSAs contained in the global structure. AS External and type-11 Opaque LSAs are omitted from a virtual neighbor's Database summary list. AS External LSAs and type-11 Opaque LSAs are omitted from the Database summary list if the area has been configured as a stub area (see Section 3.6 of [OSPF]).
 		  
  Type-9 Opaque LSAs are omitted from the Database summary list if the interface associated with the neighbor is not the interface associated with the Opaque LSA (as noted upon reception).
 		  
  Any advertisement whose age is equal to MaxAge is omitted from the Database summary list. It is instead added to the neighbor's link-state retransmission list. A summary of the Database summary list will be sent to the neighbor in Database Description packets. Each Database Description Packet has a DD sequence number, and is explicitly acknowledged. Only one Database Description Packet is allowed to be outstanding at any one time. For more detail on the sending and receiving of Database Description packets, see Sections 10.6 and 10.8 of [OSPF].  
   

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