Routing

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

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 !!

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.

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If this solves your problem, please mark this post as "Accepted Solution."
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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

thanks for clarification!

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 :).