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6256 Views 7 Replies Latest reply: Oct 20, 2011 10:36 PM by Annamalai RSS

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OSPF LSA TYPES

Oct 19, 2011 6:55 AM

Annamalai 609 posts since
Jan 1, 2011

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.

  • Martin 13,881 posts since
    Jan 16, 2009
    Currently Being Moderated
    1. Oct 19, 2011 7:07 AM (in response to Annamalai)
    Re: OSPF LSA TYPES

    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

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  • Bogdan 69 posts since
    Mar 1, 2011
    Currently Being Moderated
    3. Oct 20, 2011 1:17 AM (in response to Annamalai)
    Re: OSPF LSA TYPES

    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

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  • Roberto 1 posts since
    Aug 18, 2011
    Currently Being Moderated
    4. Oct 20, 2011 7:53 AM (in response to Bogdan)
    Re: OSPF LSA TYPES

    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

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  • Martin 13,881 posts since
    Jan 16, 2009
    Currently Being Moderated
    5. Oct 20, 2011 8:32 AM (in response to Annamalai)
    Re: OSPF LSA TYPES
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  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,426 posts since
    Oct 7, 2008
    Currently Being Moderated
    6. Oct 20, 2011 7:24 PM (in response to Annamalai)
    Re: OSPF LSA TYPES

    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

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