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Revert "ospfd: Do not fall back to intervening router."

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This reverts commit 9289c6ff55.

The commit reverted an earlier change which was fixed a bug that caused
black-holes to remote destinations with multiple paths, that could occur
during convergence. Overall, the previous code is more correct.
This commit is contained in:
Paul Jakma 2012-08-06 12:17:12 +01:00
parent 28971c8cb1
commit 945ea29339
1 changed files with 30 additions and 4 deletions
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34
ospfd/ospf_spf.c
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@ -675,11 +675,37 @@ ospf_nexthop_calculation (struct ospf_area *area, struct vertex *v,
added = 1;
ospf_spf_add_parent (v, w, nh, distance);
}
/* Always return here as we known that 16.1.1 para 4
does not apply one you have found a connection to root */
return added;
}
/* Note lack of return is deliberate. See next comment. */
}
}
/* NB: This code is non-trivial.
*
* E.g. it is not enough to know that V connects to the root. It is
* also important that the while above, looping through all links from
* W->V found at least one link, so that we know there is
* bi-directional connectivity between V and W (which need not be the
* case, e.g. when OSPF has not yet converged fully). Otherwise, if
* we /always/ return here, without having checked that root->V->-W
* actually resulted in a valid nexthop being created, then we we will
* prevent SPF from finding/using higher cost paths.
*
* It is important, if root->V->W has not been added, that we continue
* through to the intervening-router nexthop code below. So as to
* ensure other paths to V may be used. This avoids unnecessary
* blackholes while OSPF is convergening.
*
* I.e. we may have arrived at this function, examining V -> W, via
* workable paths other than root -> V, and it's important to avoid
* getting "confused" by non-working root->V->W path - it's important
* to *not* lose the working non-root paths, just because of a
* non-viable root->V->W.
*
* See also bug #330 (required reading!), and:
*
* http://blogs.oracle.com/paulj/entry/the_difference_a_line_makes
*/
if (added)
return added;
}
/* 16.1.1 para 4. If there is at least one intervening router in the