Routing

Expand all | Collapse all

OSPF LSA Type 1 questions

Jump to Best Answer
  • 1.  OSPF LSA Type 1 questions

    Posted 01-15-2020 17:31

    I am refreshing my OSPF via some Juniper trainings now.

    I have some questions about LSA type 1 fields.

    Here is my packet capture for LSA type 1

    LSA-Type-1.PNG

    Type 1 contains Link type, link ID and Link Data, Metric and etc.

    These fields are stored LSA header or Data payload.  Here I only captured the header, I could not see them. 

    Anything I have missed ?

     

    thanks !!



  • 2.  RE: OSPF LSA Type 1 questions

     
    Posted 01-15-2020 18:59

    Hi gongyayu,

     

    Yes they are part of LSA Header, see them under the "Type" in your packet:

     

    Example:

    Type: Stub ID: 192.168.20.0 Data: 255.255.255.0 Metric: 10 <<<<<<<<<<<<<<<<<<
    Link ID: 192.168.20.0 - IP network/subnet number
    Link Data: 255.255.255.0 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
    Link Type: 3 - Connection to a stub network
    Number of Metrics: 0 - TOS
    0 Metric: 10 

     

    The link data is the mask as per RFC:

     

                In addition, the Link Data field is specified for each link.
                This field gives 32 bits of extra information for the link.
                For links to transit networks, numbered point-to-point links
                and virtual links, this field specifies the IP interface
                address of the associated router interface (this is needed
                by the routing table calculation, see Section 16.1.1).  For
                links to stub networks, this field specifies the stub
                network's IP address mask.  For unnumbered point-to-point
                links, the Link Data field should be set to the unnumbered
                interface's MIB-II [Ref8] ifIndex value.

     

    Hope this helps.

    Regards,
    -r.

    --------------------------------------------------

    If this solves your problem, please mark this post as "Accepted Solution."
    Kudos are always appreciated :).

     



  • 3.  RE: OSPF LSA Type 1 questions
    Best Answer

     
    Posted 01-16-2020 00:56

    Hi,

     

    The LSA Header is present and same in all LSA types while LSA data/payload is specific to each LSA.

    LSA Header format:

           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |            LS age             |    Options    |    LS type    |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |                        Link State ID                          |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |                     Advertising Router                        |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |                     LS sequence number                        |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |         LS checksum           |             length            |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Anything after length field is part of LSA data.

    Therefore Link type, link ID and Link Data, Metric are specific to LSA Type 1 and part of LSA data, not LSA header.

     

    Cheers, 

    Ashvin



  • 4.  RE: OSPF LSA Type 1 questions

    Posted 01-16-2020 12:24

    thanks for clarification!



  • 5.  RE: OSPF LSA Type 1 questions

     
    Posted 01-16-2020 15:30
    Hi gongyayu, please mark appropriate post as accepted solution if you could. It will add value to someone reading your post at a later time. Hope you agree!

    Hope this helps.

    Regards,
    -r.

    --------------------------------------------------

    If this solves your problem, please mark this post as "Accepted Solution."
    Kudos are always appreciated :).