7 Replies Latest reply: Oct 20, 2011 10:36 PM by Annamalai RSS

    OSPF LSA TYPES

    Annamalai

      Hi Friends

      I have lost myself in the OSPF LSA types.

      Can you please post a video for the LSA types.With a senario explanation.

      Thank you.

        • 1. Re: OSPF LSA TYPES
          Martin

          For all types of LSAs, there are 20-byte LSA headers. One of the fields of the LSA header is the link-state ID.

           

          Every router generates router link advertisements for each area to which it belongs.

           

          Type 1 ( O )

           

          Router link advertisements describe the state of the links of the router to the area and are flooded only within a particular area. The link-state ID of the type 1 LSA is the originating router ID.

           

          Type 2  ( O )

           

          DRs generate network link advertisements for multi-access networks that describe the set of routers attached to a particular multi-access network. Network link advertisements are flooded in the area that contains the network. The link-state ID of the type 2 LSA is the IP interface address of the DR.

           

          Types 3 ( OIA )

           

          ABRs generate summary link advertisements.  

           

          These LSAs are flooded throughout the backbone area to the other ABRs. These link entries are not flooded into totally stubby areas or not-so-stubby areas (NSSAs).

           

          The link-state ID for type 3 LSAs  is the destination network

           

          Types 4( OIA )

           

          I s generated by an ABR only when an ASBR exists within an area, It describes routes to ASBRs.

           

          Its mainly used to let the ASBR reachable by all other Areas.

           

          These link entries are not flooded into totally stubby areas or not-so-stubby areas (NSSAs).

           

          The link-state ID for type 4 LSAs  is the  router ID of ASBR.

           

          Type 5 ( OE1 & OE2 )

           

          ASBRs generate AS external link advertisements. External link advertisements describe routes to destinations external to the AS and are flooded everywhere with the exception of stub areas, totally stubby areas, and NSSAs ,

           

          Type 4 LSA is needed to find the ASBR.

           

          The link-state ID of the type 5 LSA is the external network number.

           

          Type 6

           

          Type 6 LSAs are specialized LSAs that are used in multicast OSPF applications. (Group membership LSA)

           

          Type 7

           

          Type 7 is an LSA type that is used inside NSSAs. , its then Converted by the ABR to type 5 LSA.//////////

           

           

           

          Type 8

           

          Type 8 is a specialized LSA that is used in internetworking OSPF and Border Gateway

           

          Protocol (BGP).

           

          Types 9, 10, and 11

           

          The opaque LSAs, types 9, 10, and 11, are designated for future upgrades to OSPF for

           

          application-specific purposes. For example, Cisco Systems uses opaque LSAs for

           

          Multiprotocol Label Switching (MPLS) with OSPF. Standard LSDB flooding mechanisms are

           

          used for distribution of opaque LSAs. Each of the three types has a different flooding scope.

           

           

           

           

           

           

          https://learningnetwork.cisco.com/docs/DOC-12541

          • 2. Re: OSPF LSA TYPES
            Annamalai

            Hello Martin

            Thanks for the kind information.

            But still i'm getting confuse in the SHOW IP OSPF DATABASE command.

            I'm not able to understand the database and its LSA types.

            Theory wise i'm bit clear.I'm not able to predict which is LAS1,2....etc in the database.

            And one more doubt please clear this also.

            How the router will find whether to to elect DR or not?

            How the router will know whether its a Broadcast network or Point-to-Point network?

            • 3. Re: OSPF LSA TYPES
              Bogdan

              On LSA Types if you got the theory you should be able to read through a ospf database.

              I recomend you read the Official Certification Guide for CCNP Route first OSPF chapter covers LSA Types.

               

              On your last 2 questions.

              How the router will find whether to to elect DR or not? It looks at the network type.

              How the router will know whether its a Broadcast network or Point-to-Point network? There are default network types ,like for ethernet the default is brodcast, and you can also change the default for whatever suits your needs.

               

              You shold know OSPF network types:

               

              Broadcast:

               

              Default on Ethernet

              Hello interval 10 seconds

              Dead Interval 40 seconds

              DR/BDR election

              Updates are sent as multicast

              Next hop  is not changed and remains the ip address of the originating router

               

               

              Non-Broadcast:

               

              Default on Multipoint interface like Frame-relay

              Hello interval 30 seconds

              Dead Interval 120 seconds

              DR/BDR election

              Updates are sent as unicast

              Neighbor command required on hub router

              Next hop is not changed and remains the ip address of the originating router

               

              Point to Point:

               

              Default on HDLC, PPP and Frame-relay Point-to-Point

              Hello Interval 10 seconds

              Dead Interval 40 seconds

              No DR/BDR Election

              Multicast updates to 224.0.0.5

              Next hop address is that of the advertising router

               

               

              Point to Multipoint Broadcast:

               

              Cisco proprietary

              Host routes are added in the routing table

              Hello Interval 30 seconds

              Dead Interval 40 seconds

              No DR/BDR Election

              Multicast updates to 224.0.0.5

              Next hop address is that of the advertising router

              Frame-relay partial mesh

               

               

              Point to Multipoint Non-Broadcast:

               

              Cisco proprietary

              Hello Interval 30 seconds

              Dead Interval 120 seconds

              Frame-relay Partial Mesh

              No DR/BDR Election

              Unicast updates

               

               

              Bogdan

              • 4. Re: OSPF LSA TYPES
                Roberto

                Hi just a little clarification here on the OSPF network types:

                 

                Point to Multipoint Broadcast is not Cisco proprietary, it's defined by the RFC 2328, together with the Non Broadcast Multi Access.

                 

                Broadcast, Point-to-Point and Point to Multipoint Non Broadcast network types are Cisco.

                 

                Robby

                • 5. Re: OSPF LSA TYPES
                  Martin
                  • 6. Re: OSPF LSA TYPES
                    Scott Morris - CCDE/4xCCIE/2xJNCIE

                    I'm not able to understand the database and its LSA types.

                    Theory wise i'm bit clear.I'm not able to predict which is LAS1,2....etc in the database.

                     

                    Any place you have a DR, you'll get Type 2's.

                     

                    If you have an area with only ethernet segments (and the default broadcast ospf network type) you'll have mostly type 2's in your database (except for the router-id type 1's).

                     

                    If you have an area with NO ethernet segments (or no network types using a DR), then you'll have NO type 2's and everything will be a type 1 advertisement.

                     

                    Each one can advertise a link.  Just different based on who does it!

                     

                    HTH,

                     

                    Scott

                    • 7. Re: OSPF LSA TYPES
                      Annamalai

                      Thank you friends

                      Now I'm clear.

                      Today I'll do all the Network type senario and ill go through the OSPF Database and its LSA TYPES .

                      Hope I'll understand the database.

                      Wish me luck friends.

                      Again Thanks a lot friends.