4 Replies Latest reply: May 25, 2009 8:08 PM by Krzysztof Przybylski RSS

    EIGRP-TLV vs. Header Fields


      Hello All,


      I need clarification on the nuances between the EIGRP header fields and EIGRP Type/Length/Values.


      Here's my contention:


      EIGRP Header Field contains an Version Field, Sequence Field, and Acknowledement Field; which also seem to be delineated within the Type/Length/Value Field with: 0x0003-Sequence; 0x0004-EIGRP Software Version; 0x0005-Next Multicast Sequence.  Why the seeming redundancy between the Header and the Message/Data/TLV field?



        • 1. Re: EIGRP-TLV vs. Header Fields
          Krzysztof Przybylski




          TLV packets (quite similar to TLVs in isis) are responsible for future extensions of the EIGRP protocol.

          So TLV carry additional info

          for example: SIAquery/reply, IOS info, sequencing, informations for DUAL, management info or IPv6

          (thats why IMHO isis is better than ospf)

          TLV also take a part in Internal and external routes processes, they are responsible for carrying the route entires.




          Hope it helps You.




          - Krzysztof Przybylski

          • 2. Re: EIGRP-TLV vs. Header Fields
            Krzysztof Przybylski

            Hello again !


            I guess I didn't answer your question directly.


            In my opinion this redudancy occurs because:



            EIGRP TLV beneffit --> If you need aditional EIGRP extension, then you need only 'implement plugin' to EIGRP protocol. This 'plugin' is TLV data. As you can imagine, when you implement for example IPv123 the header still is the same.

            It can be IPv6 , auth, IPX, .....etc etc ...  extension.

            Sometimes it's necesary to rewrite mentioned header data with the new ones from TLV.

            And its all



            I hope it helps You.







            • 3. Re: EIGRP-TLV vs. Header Fields

              Hi Krzysztof,


              I thank you for your response!  It's not that you didn't answer my question initially directly; I was hoping for a little more input on the topic and maybe an official Cisco document before fully awarding the points.  Since there were no other takers you get all the points!


              Best Regards,



              • 4. Re: EIGRP-TLV vs. Header Fields
                Krzysztof Przybylski



                It's very difficult to find any comprehensive information related exactly with EIGRP Header/TLV's functions, relationships, processes.

                I think that only some security specialists have got suitable knowledge to explain those connections in details.

                And I suppose that in all Cisco Security track, there is nothing about it.



                Best Regards,