I hope I'm not confusing the issue here.....
I plugged your config into my pod, with a few minor changes
(interface types used). I used serials thorughout the net, where
you used some ethernet interfaces, with the exception of RouterD
where I used a loopback interface instead of the ethernet you used!
Here's my config and RouterA's routing table.
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
!
router ospf 10
network 192.168.1.0 0.0.0.255 area 1
end
!
hostname RouterB
!
interface Serial0
description connected to RouterA via network 1
ip address 192.168.1.1 255.255.255.0
ip ospf cost 1
!
interface Serial1
description connected to RouterC via network 2
ip address 192.168.2.1 255.255.255.0
ip ospf cost 4
!
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
end
!
hostname RouterC
!
interface Serial0
description connected to RouterB via network 2
ip address 192.168.2.2 255.255.255.0
ip ospf cost 4
!
interface Serial1
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
end
!
hostname RouterD
!
interface Loopback0
description network 4
ip address 192.168.4.1 255.255.255.0
ip ospf network point-to-point
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
!
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
end
RouterA#sh 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
O IA 192.168.4.0/24 [110/85] via 192.168.1.1, 00:02:50, Serial0
C 192.168.1.0/24 is directly connected, Serial0
O IA 192.168.2.0/24 [110/5] via 192.168.1.1, 00:02:50, Serial0
O IA 192.168.3.0/24 [110/69] via 192.168.1.1, 00:02:50, Serial0
As you can see, I got the results expected!
I am very curious why you're getting the results you posted, but I
can't reconfig my pod right now to match your exact setup without
sabotaging another issue I'm trying to resolve.
Stefan
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Diffy De Villiers
Sent: Wednesday, January 16, 2002 9:23 AM
To: [EMAIL PROTECTED]
Subject: RE: URGENT - PLEASE HELP - OSPF summary route cost. [7:31832]
Hi Andrew,
Thank you for you willingness to assist.
Someone in the group suggested that a routing loop may exists (i.e,
the path Router A uses to get to network 3 is via B via C via D to
network 3). Although this may explain the extra cost factor of 64, this
is not what happens as can be seen from the following two traceroute
outputs:
RouterA>traceroute 192.168.3.1
Tracing the route to 192.168.3.1
1 192.168.1.1 4 msec 4 msec 4 msec
2 192.168.2.2 8 msec 8 msec *
RouterA>traceroute 192.168.3.2
Tracing the route to 192.168.3.2
1 192.168.1.1 4 msec 4 msec 4 msec
2 192.168.2.2 8 msec 4 msec 4 msec
3 192.168.3.2 8 msec 8 msec *
As you can see the optimal path is used everytime (i.e. Router A to B
to C to network 3).
When examining the Link-State Databases of the routers in Area 0,
network 3 has a metric of 128 (and not 64 as would have been expected).
Similarly network 1 has a cost of 2 (and not 1). Why is the costs of
these two summary routes doubled?.
Kind Regards
Diffy de Villiers
>>> "Andrew Larkins" 01/14/02 01:53PM
>>>
Hi,
I am not to sure myself here. I will ask one of my colleagues here as
well
to see if he has any light that he can shed here.
Regards
Andrew
-----Original Message-----
From: Diffy De Villiers [mailto:[EMAIL PROTECTED]]
Sent: 14 January 2002 13:01 PM
To: [EMAIL PROTECTED]
Subject: URGENT - PLEASE HELP - OSPF summary route cost. [7:31832]
Hi Everybody
This is the third time that I am posting this message to this
studygroup,
I had no reply to the previous two postings. Hopefully someone will be
able to assist me this time.
I have a problem understanding how costs are calculated for OSPF
summary
routes. To understand my problem refer to the following example:
This is the internetwork diagram (with 4 routers A,B,C & D):
netw 1 netw 2 netw 3 netw 4
[ A ]--------[ B ]--------[ C ]---------[ D ]---------|
cost 1 cost 4 cost 64 cost 16
----------------------------------
Here are my router configurations:
----------------------------------
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
--------------------------------------
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=32192&t=31832
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