Hi Pat,
if this rule is supposed to be applied only to LSAs with the same fw
address then it can be reached only when two Type-7 LSAs originated
within the same area are being compared. Because if we are comparing
Type-5 and Type-7 with equal fw address then at least one of LSAs will
be rejected at the step 3. Fw address is reachable either thru NSSA area
(then Type-5 is rejected) or through 'normal' area (and then Type-7 is
rejected).
---
Thanks,
Anton
Pat Murphy - (650)329-4044 wrote:
In RFC 3101 (NSSA option), section 2.5.6 (e) for calculating External
LSA states;
(e) If the current LSA is functionally the same as an
installed LSA (i.e., same destination, cost and non-zero
forwarding address) then apply the following priorities in
deciding which LSA is preferred:
1. A Type-7 LSA with the P-bit set.
2. A Type-5 LSA.
3. The LSA with the higher router ID.
[NSSA]
My doubt is:
If the both LSAs have zero FA or different FA then should
the above preference rule be skipped and both LSAs be
considered for SPF?
That is correct. Once the (6)a through (6)e preference rules are applied
to the installed LSAs and the current LSA under external calculation,
some of the installed LSAs may be replaced in the installed set by the
current LSA. Alternatively the current LSA may not be installed and the
existing installed set may remain intact, or the LSA may be added to the
existing installed set. If the forwarding addresses of the installed set
are all different, then this preference rule simply does not prune any
LSAs from the combined set. If an LSA has a zero FA then this preference
rule is skipped.
Pat
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