From: Stefan L. Dozier (doziersl@yahoo.com)
Date: Fri Dec 27 2002 - 01:12:44 GMT-3
Reference: Parkhurst's OSPF Command and Configuration Handbook
I need to bounce this off the list just to help clear up
some confusion on my part:
Basic 3 router network, Routers A, B, and C
Configuration posted on the end of the message!
The gist of the scenario demonstrates how adjusting (lowering)
the admin distance of OSPF allows the 3.3.3.0/24 advertised
from RouterA to be placed in the routing table of RouterB vice
the eigrp derived 3.3.3.0/24 network from RouterC.
Entering "distance 80" under the OSPF process on RouterB causes
an instant spf recalc and the 3.3.3.0/24 from RouterA is placed
in RouterB's routing table. *No issues here*
Cleaning up the scenario to default, and entering
"distance 80 1.1.1.1 0.0.0.0" under the OSPF process on RouterB
does not cause an instant spf recalc and requires a
"clear ip ospf 1 process" command to get the 3.3.3.0/24 network
from RouterA into RouterB's routing table!
*OK, strange, but I've move on for now!
Cleaning up the scenario to default, and entering
"distance 80 1.1.1.1 0.0.0.0 1" under the OSPF process on RouterB
but before I actually defined "access-list 1" requires a "clear ip
ospf 1 process" command [*not surprised] and actually sets the
admin distance of 3.3.3.0/24 to 80 which allows the 3.3.3.0/24
network into RouterB's routing table via ospf from RouterA.
*Now I'm confused*
I'm thinking, since I instructed the distance command to use
access-list 1 but didn't actually define access-list 1,
and with access-lists default to implicitly deny all, that
no routes from RouterA would make it into RouterB's routing
table, and the opposite happened. It set the admin distance
on all ospf routes from RouterA to 80 and placed them in the
routing table.
RouterA
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Loopback1
ip address 3.3.3.3 255.255.255.0
ip ospf network point-to-point
!
interface TokenRing0/0
ip address 172.16.1.1 255.255.255.0
ip mtu 4464
ring-speed 16
!
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 3.3.3.0 0.0.0.255 area 0
network 172.16.1.0 0.0.0.255 area 0
RouterB
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Serial1
bandwidth 64
ip address 10.1.1.5 255.255.255.252
clockrate 64000
!
interface TokenRing0
ip address 172.16.1.2 255.255.255.0
ring-speed 16
!
router eigrp 1
network 10.0.0.0
no auto-summary
eigrp log-neighbor-changes
!
router ospf 1
log-adjacency-changes
network 2.2.2.2 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 0
RouterC
interface Loopback0
ip address 3.3.3.3 255.255.255.0
!
interface Serial0
bandwidth 64
ip address 10.1.1.6 255.255.255.252
no fair-queue
!
router eigrp 1
network 3.0.0.0
network 10.0.0.0
no auto-summary
eigrp log-neighbor-changes
.
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