From: Scott Morris (swm@emanon.com)
Date: Mon May 23 2005 - 23:01:43 GMT-3
Per the RFC, intra-area routes are ALWAYS preferred over inter-area, which
are always preferred over external LSAs. This choice is done prior to
looking at the cost associated with it.
Think of it like going by LSA number first, cost/metric later.
Type 1/2, then type 3, then type 5.
HTH,
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Golia, Jeff
Sent: Monday, May 23, 2005 9:44 PM
To: Group Study (E-mail)
Subject: OSPF Route Selection
Hello,
Hopefully you can help explain some OSPF behavior. I am experiencing a
router preferring Intra-area L3 LSAs with a higher metric, over Inter-area
L3 LSAs with a lower metric. Is this normal?
Other clues to the topology follow, along with bad ascii art ;)
R3 ~ISDN~ R5
| /
Frame Frame
| /
R1
The ISDN link is area 13. The R1R3 frame is area 12. The R1R5 frame is
area 0.
The route I am describing is R1 Loopback, which is in area 0. R3 chooses
the high cost ISDN path over the low-cost inter-area R1R3 frame path.
Virtual-Link through ISDN. The cost on both bri0 ints is 9999. When the
ISDN is up, the adjacencies form, and the high cost routes enter the routing
table. R3 will prefer the high cost Intra-area route over a much lower cost
Inter-area route. It doesn't matter which backup method I use to bring up
the ISDN, still experience this behavior. Is this normal behavior? The
ISDN is intra-area because the virtual link creates an extension of area 0.
If R1 Loopback is moved to area 12 R3 will then prefer the lower-cost R1R3
Frame intra-area route.
Thanks In Advance ; sorry for the long read!
Jeff Golia, CCNP MCSE
Network Administrator
Transworld Port and Distribution Services Wilmington, Delaware
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