Re: [OSPF] Options field in hello packet with regard to Opaque capability

On Jul 18, 2008, at 11:15 AM, Varghese John wrote:

Hello,
I am trying to find the standard way to specify the opaque LSA capability in the OSPF packets.

RFC 2370, which describes the opaque option (section 3.1).

   "An opaque-capable router learns of its neighbor's opaque capability
   at the beginning of the "Database Exchange Process" (see Section 10.6
   of [OSPF], receiving Database Description packets from a neighbor in
   state ExStart). A neighbor is opaque-capable if and only if it sets
   the O-bit in the Options field of its Database Description packets;
   the O-bit is not set in packets other than Database Description
   packets. Then, in the next step of the Database Exchange process,
   Opaque LSAs are included in the Database summary list that is sent to
   the neighbor (see Sections 3.2 below and 10.3 of [OSPF]) if and only
   if the neighbor is opaque capable."

   This specifies Opaque option is set only in database description packet.

RFC 5250, which describes the opaque option (section 3.1).
   "An opaque-capable router learns of its neighbor's opaque capability
   at the beginning of the "Database Exchange Process" (see Section 10.6

   of [OSPF] regarding receiving Database Description packets from a
   neighbor in state ExStart).  A neighbor is opaque-capable if and only

   if it sets the O-bit in the Options field of its Database Description
   packets; the O-bit SHOULD NOT be set and MUST be ignored when
   received in packets other than Database Description packets.  Using
   the O-bit in OSPF packets other than Database Description packets

   will result in interoperability issues.  The setting of the O-bit is
   a "SHOULD NOT" rather than a "MUST NOT" to remain compatible with
   earlier specifications."


   Here I understand some implementations have the opaque option set in other than the database descripiton packet.

Correct - and others don't set the O-bit in other OSPF packet types. We had a discussion about this on the list while the draft was in review. Our conclusion was that the O-bit really only needed to be set in the options field for Database Exchange packets. I might have left this alone if I were doing the update but the authors felt the RFC 2370 ambiguity needed to be cleared up. Everyone has agreed on the current text which allows backward compatibility.




   Would some one tell me which specifications has the Opaque LSA options set in other fields???
   And also do we need to specify the Opaque LSA capability in the hello packet options field??

By "earlier specifications", it refers to RFC 2370 which was ambiguous on the setting of the O-bit in packets other than Database Exchange packets.

Thanks,

Acee

thanks

-varghese

   
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