Thank you to everybody who responded to my earlier email.
I realize that a picture says more than a thousand words,
therfore I am supplementing my earlier questions with the
following scenario:
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Here are my router configurations:
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hostname RouterA
!
interface Serial0
description connected to RouterB via network 1
ip address 192.168.1.2 255.255.255.0
ip ospf cost 1
no fair-queue
!
router ospf 10
network 192.168.1.0 0.0.0.255 area 1
--------------------------------------
hostname RouterB
!
interface Ethernet0
description connected to RouterC via network 2
ip address 192.168.2.1 255.255.255.0
ip ospf cost 4
!
interface Serial0
description connected to RouterA via network 1
ip address 192.168.1.1 255.255.255.0
ip ospf cost 1
!
router ospf 10
network 192.168.1.0 0.0.0.255 area 1
network 192.168.2.0 0.0.0.255 area 0
--------------------------------------
hostname RouterC
!
interface Ethernet0
description connected to RouterB via network 2
ip address 192.168.2.2 255.255.255.0
ip ospf cost 4
!
interface Serial0
description connected to RouterD via network 3
ip address 192.168.3.1 255.255.255.0
ip ospf cost 64
!
router ospf 10
network 192.168.2.0 0.0.0.255 area 0
network 192.168.3.0 0.0.0.255 area 2
--------------------------------------
hostname RouterD
!
interface Ethernet0
description network 4
ip address 192.168.4.1 255.255.255.0
ip ospf cost 16
!
interface Serial0
description connected to RouterC via network 3
ip address 192.168.3.2 255.255.255.0
ip ospf cost 64
no fair-queue
!
router ospf 10
network 192.168.3.0 0.0.0.255 area 2
network 192.168.4.0 0.0.0.255 area 2
--------------------------------------
The network diagram follows:
netw 1 netw 2 netw 3 netw 4
[ A ]--------[ B ]--------[ C ]---------[ D ]---------|
cost 1 cost 4 cost 64 cost 16
---------------------------------------
If we do a "show ip route" at routerA we get the following output:
RouterA>show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B -
BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate
default
U - per-user static route, o - ODR
Gateway of last resort is not set
C 192.168.1.0/24 is directly connected, Serial0
O IA 192.168.2.0/24 [110/5] via 192.168.1.1, 00:23:26, Serial0
O IA 192.168.3.0/24 [110/133] via 192.168.1.1, 00:18:51, Serial0
O IA 192.168.4.0/24 [110/85] via 192.168.1.1, 00:18:56, Serial0
Now for my problem:
Looking at the diagram above, the metric from Router A to network 4 is
85.
This is perfectly understandable (sumtotal of all the costs: 85 =
1+4+64+16).
BUT NOW: The metric from RouterA to network 3 is 133!!! This is higher
than the metric to network 4 even though we access network 4 via network
3.
Logically I would have thought the cost to network 3 has to be 69
(64+4+1), not 133. Where does the cost-difference of 64 come from? The
only rational explanation I have for this is that the ABR for area 2
added it, but why??? And why only add this cost factor for network 3
(and not for network 4)???
Please assist me if you know the answers since I cannot figure out a
reasonable explanation.
Thank you for your support.
Abraham de Villiers
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=30523&t=30297
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