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KATTUBAVA E.S
Beginner

OSPF LSA-9 Confusion

Hi Experts,

OSPF LSA-9 is defined for Opaque LSA for Link-local flooding scope, at the same time I could see LSA-9 is also defined for carrying Intra-Area prefix in OSPFv3 domain. Its bit confusing that how come a single LSA is defined for two different purpose? Can someone me the use case of this LSA-9?

I have noticed Cisco IOS is neither using LSA-9 or LSA-11 for both Intra-Area and Inter-Area MPLS TE scenarios. Furthermore IPv6 OSPF implementation i.e OSPFv3 database is using both Link(LSA-8) and Intra-Area prefix (LSA-9) LSA in its database but Intra-Area Prefix LSA alone not marked as LSA-9.

snippet:

Link (Type-8) Link States (Area 0)

ADV Router Age Seq# Link ID Interface

1.1.1.1 11 0x80000002 3 Et0/0

Intra Area Prefix Link States (Area 0)

ADV Router Age Seq# Link ID Ref-lstype Ref-LSID
1.1.1.1 10 0x80000002 0 0x2001 0

1 ACCEPTED SOLUTION

Accepted Solutions
Peter Paluch
Hall of Fame Cisco Employee

Hi,

Opaque LSA types have only been standardized for OSPFv2. There are no opaque LSA types in OSPFv3 because OSPFv3 has been designed from beginning to gracefully handle unknown LSA types. The flooding scope of an unknown LSA in OSPFv3 is in fact encoded in its type which is now 2 bytes long (as opposed to OSPFv2 LSA type field that was only 1 byte long). Even if an OSPFv3 router does not recognize the type of the received LSA, the type field of this LSA carries bits that describe how this LSA shall be flooded. This, together with the significantly larger number space provided by the extended type field, obviates the need for opaque LSAs in OSPFv3.

As similar as it is, LSA numbering in OSPFv2 and OSPFv3 is independent of each other. You shouldn't assume that Type 9 LSA in OSPFv2 has the same use and meaning in OSPFv3. In fact, there is no Type 9 LSA in OSPFv3. The true type of the Intra-Area-Prefix LSA is 0x2009, not 0x0009. The '9' is the LSA Functional Code enumerating the LSA type and purpose, while the '2' at the beginning states that this LSA has an area-wide flooding scope.

IANA maintains a registry of currently defined OSPFv3 LSA functional codes and you can find it on the following URL:

http://www.iana.org/assignments/ospfv3-parameters/ospfv3-parameters.xhtml#ospfv3-parameters-3

There are also ranges available for experimentation and vendor private use.

Please feel welcome to ask further!

Best regards,
Peter

View solution in original post

4 REPLIES 4
KATTUBAVA E.S
Beginner

Can someone help me to understand this?

Peter Paluch
Hall of Fame Cisco Employee

Hi,

Opaque LSA types have only been standardized for OSPFv2. There are no opaque LSA types in OSPFv3 because OSPFv3 has been designed from beginning to gracefully handle unknown LSA types. The flooding scope of an unknown LSA in OSPFv3 is in fact encoded in its type which is now 2 bytes long (as opposed to OSPFv2 LSA type field that was only 1 byte long). Even if an OSPFv3 router does not recognize the type of the received LSA, the type field of this LSA carries bits that describe how this LSA shall be flooded. This, together with the significantly larger number space provided by the extended type field, obviates the need for opaque LSAs in OSPFv3.

As similar as it is, LSA numbering in OSPFv2 and OSPFv3 is independent of each other. You shouldn't assume that Type 9 LSA in OSPFv2 has the same use and meaning in OSPFv3. In fact, there is no Type 9 LSA in OSPFv3. The true type of the Intra-Area-Prefix LSA is 0x2009, not 0x0009. The '9' is the LSA Functional Code enumerating the LSA type and purpose, while the '2' at the beginning states that this LSA has an area-wide flooding scope.

IANA maintains a registry of currently defined OSPFv3 LSA functional codes and you can find it on the following URL:

http://www.iana.org/assignments/ospfv3-parameters/ospfv3-parameters.xhtml#ospfv3-parameters-3

There are also ranges available for experimentation and vendor private use.

Please feel welcome to ask further!

Best regards,
Peter

View solution in original post

Thanks for your help Peter!

3.0 The Opaque LSA

   Opaque LSAs are types 9, 10 and 11 link-state advertisements.  Opaque
   LSAs consist of a standard LSA header followed by a 32-bit aligned
   application-specific information field.  Standard link-state database
   flooding mechanisms are used for distribution of Opaque LSAs.  The
   range of topological distribution (i.e., the flooding scope) of an
   Opaque LSA is identified by its link-state type.  This section
   documents the flooding of Opaque LSAs.

   The flooding scope associated with each Opaque link-state type is
   defined as follows.

     o Link-state type 9 denotes a link-local scope. Type-9 Opaque
       LSAs are not flooded beyond the local (sub)network.

     o Link-state type 10 denotes an area-local scope. Type-10 Opaque
       LSAs are not flooded beyond the borders of their associated area.

     o Link-state type 11 denotes that the LSA is flooded throughout
       the Autonomous System (AS). The flooding scope of type-11
       LSAs are equivalent to the flooding scope of AS-external (type-5)
       LSAs.  Specifically type-11 Opaque LSAs are 1) flooded throughout
       all transit areas, 2) not flooded into stub areas from the
       backbone and 3) not originated by routers into their connected
       stub areas.  As with type-5 LSAs, if a type-11 Opaque LSA is
       received in a stub area from a neighboring router within the
       stub area the LSA is rejected.
Ref: https://tools.ietf.org/html/rfc2370