Hi Stefan, Thank you for all your assistance on this topic, but I found the answer to my questions. Peter van Oene pointed me to a bug which existed in the IOS before 11.3 (sorry for the typo error earlier- I'm using 11.2 not 11.3). Here are the details as pointed out by Peter:
Bug ID CSCdi70406 Bug Details: OSPF ABR will generate summary for subnet of connected point-to-point interface with wrong cost. The wrong cost is twice as much as the actual OSPF cost of the interface. In topology with more that one ABR, this could create routing loop for the point-to-point interface subnet. In order words, attempt to telnet or to ping the point-to-point interface address from a different area could fail, but the router could still be accessed through other non-point-to-point interface addresses on the router. There is no workaround. Once again, thank you to everyone who assisted with this problem. Diffy >>> "Stefan Dozier" 01/18/02 05:18PM >>> 12.0(20) on one router and 12.1(12) on the rest! Which 11.3 version are you running? -Stefan -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Diffy De Villiers Sent: Friday, January 18, 2002 4:04 AM To: [EMAIL PROTECTED] Subject: RE: URGENT - PLEASE HELP - OSPF summary route cost. [7:31832] Hi Stefan, Thank you for your input, but indeed things is more confusing now!!! I am glad to see that you got the expected results. Maybe the implementation differences lies in the version of IOS. I am using IOS 11.3 (what version are you using?). Kind Regards Diffy >>> "Stefan Dozier" 01/16/02 07:19PM >>> 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=32534&t=31832 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
