[Xorp-hackers] route calculation: next hop's interface address ?

Selçuk Cevher cevhers at gmail.com
Fri Jul 11 06:31:12 PDT 2008

Hi All,

As you know, to compute the routes to all destinations in the network, an
ospf router creates an Spt object, and adds itself to it as the root
(area_router.cc). Then, the source router sets some relevant information
such as version, node id, origin, type, and more importantly the LSA for
each node added to the Spt object including itself.

Then, it calls compute() function on Spt object, and finds the routes to all

However, under the assumtion that I have the entire link state advertisement
database, I want to identify one of destinations in the network as the root
of my own Spt object, rather than "myself"  (So, I will compute routes for
somebody else).
(For example, If router A (i.e., "myself") is the router computing the
routes, A creates an Spt object and sets B, one of the destinations in the
network, as the root of the Spt object).

Even though A ("myself") makes the necessary settings (LSA, version, type,
router ID, etc.) properly for B (of course, B's LSA should be obtained from
the link state database), the interface addresses of the next hops of
calculated routes for B show up as zero (
However, router ID's for the destinations and next hops are correct (I
already know the network topology).

If my question does not lack sufficient information, what may be causing the
interface addresses of the next hops to show up as when computing
the routes for somebody else ?
(When computing the routes for myself, next hop interface addresses look

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