From: ccie2be (ccie2be@nyc.rr.com)
Date: Tue Jan 18 2005 - 19:47:21 GMT-3
Hi guys,
If for some reason (like the cisco lab, for example), I needed to change ospf
default order of preference as shown
below, is that possible? If so, how could that be done?
TIA, Tim
Page 506 of "Cisco IP Routing" by Alex Zinin (good book - Buy it!!)
"In some situations, the same IP prefix may be described by LSAs
of more than one type. In this case, the calculating router has
to decide which route type should be preferred. OSPF defines
route preference rules as follows.
o Intra-area routes are always most preferred.
o Inter-area routes are preferred over AS or
NSSA external routes.
o AS-external routes and NSSA-external routes
are of equal preference. Within this set
of routes, preferences are defined as follows.
- Type 1 routes are always preferred
over type 2 ones.
- Within type 2 routes, the route metric
and the distance to the orginating router
are used as the tiebreakers.
- If the tie is still not resolved, the
following priorities are applied.
= AS-external (type 5) routes are preferred
over NSSA external (type 7) ones.
= Routes derived from type 7 LSAs with
a nonzero forwarding address
and P bit set are preferred.
o If these rules do not solve the tie,
routes are installed in parallel."
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