If we have to enable SPT in OSPF domain what is the recomandation to enable SPT on which routers ?

plz check if i am rong

only on backbone routers (Routers Belong to area 0 )

and wt if there is no router that only belong to area 0 i mean if all the routers in area 0 are ABR as well so still we can enable SPT on them ?


  • Can you clarify what do you mean by enabling SPT?

    I think your question is related to ISPF, a feature that enables incremental SPF computation for SPT calculation instead of running full SPF algorithm.

  • Saqib.....

    yup right saqib....i just want to know that which router are eligable to enable this feature...as much i understand abt this feature u have to enable ispf only on backbone routers...(wt if all the backbone routers are ABR as well)but still unable to find any Docoment on Doc CD. They have explaned the feature PRETTY well but what is missing there is which routers are eligble for this feature.

  • You can enable it on any router. It effects the local router only. Also ISPF only runs for LSA-1 or LSA-2.

    From the labs point of view, read the question carefully.

    If the question specifies a router, enable it on that router only.

    If it is asked for an area, configure it on all routers in that area including ABRs.


    it means it is not spacifice for any particular area or router.....but still saqib little confuse abt this......do u have any docs related to this Tech ?

  • Yeah it is specific to LSAs Type-1 and Type-2 regardless of areas.

    The only limitation is that if change occurs in the local router's LSAs, full SPF will run instead of ISPF.

    I believe you can specify the levels if you are using it for IS-IS but nothing like that in OSPF.

    Not aware of any other specific document but as you noted, Cisco Doc is quite clear about it.

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