From: Vytautas Valancius (valas@mail.lt)
Date: Wed Dec 22 2004 - 11:34:13 GMT-3
Hi,
OSPF prefers intra-area routes over inter-area routes, disregarding the
cost.
Best Regards,
Vytautas Valancius
----- Original Message -----
From: <gladston@br.ibm.com>
To: <ccielab@groupstudy.com>
Sent: Wednesday, December 22, 2004 3:52 PM
Subject: OSPF Cost
> R7 is an ABR router connected to R3 via tunnel interface on area 0 and
> connected to the same R3 via connected interface on a nonbackbone area. R7
> cost to a R3's route 172.16.123.0 is much bigger than R6 cost to the same
> route. R6 uses R7 to reach R3's route.
> R7 uses the tunnel interface cost on the calculation while R6, even though
> uses R7 path, does not use this cost; R6 uses the physically cost between
> R7 and R3.
>
> Any doc recommendation to understand this behavior?
>
> r7#sir 172.16.123.0
> Routing entry for 172.16.123.0/24
> Known via "ospf 1", distance 110, metric 11175, type intra area
> Last update from 172.16.137.3 on Tunnel36, 00:09:17 ago
> Routing Descriptor Blocks:
> * 172.16.137.3, from 3.3.3.3, 00:09:17 ago, via Tunnel36
> Route metric is 11175, traffic share count is 1
>
> r6#sir 172.16.123.0
> Routing entry for 172.16.123.0/24
> Known via "ospf 1", distance 110, metric 139, type inter area
> Last update from 172.16.67.7 on Serial1, 00:07:33 ago
> Routing Descriptor Blocks:
> * 172.16.67.7, from 3.3.3.3, 00:07:33 ago, via Serial1
> Route metric is 139, traffic share count is 1
>
>
> r6-----r7-----(tunnel and direct connection)----r3
>
> The direct connection is nonbackbone area
> The tunnel is backbone area.
>
> The summary LSA for the route is almost the same on both r6 and r7; the
> difference is the message "Routing Bit Set on this LSA" on r6.
>
> r7#sh ip os database summary
>
> LS age: 991
> Options: (No TOS-capability, DC, Upward)
> LS Type: Summary Links(Network)
> Link State ID: 172.16.123.0 (summary Network Number)
> Advertising Router: 3.3.3.3
> LS Seq Number: 8000002E
> Checksum: 0x8308
> Length: 28
> Network Mask: /24
> TOS: 0 Metric: 64
>
> LS age: 1589
> Options: (No TOS-capability, DC, Upward)
> LS Type: Summary Links(Network)
> Link State ID: 172.16.123.0 (summary Network Number)
> Advertising Router: 7.7.7.7
> LS Seq Number: 80000001
> Checksum: 0xF322
> Length: 28
> Network Mask: /24
> TOS: 0 Metric: 11175
>
> r6#sh ip os database summary
>
> Routing Bit Set on this LSA
> LS age: 1042
> Options: (No TOS-capability, DC, Upward)
> LS Type: Summary Links(Network)
> Link State ID: 172.16.123.0 (summary Network Number)
> Advertising Router: 3.3.3.3
> LS Seq Number: 8000002E
> Checksum: 0x8308
> Length: 28
> Network Mask: /24
> TOS: 0 Metric: 64
>
> LS age: 1639
> Options: (No TOS-capability, DC, Upward)
> LS Type: Summary Links(Network)
> Link State ID: 172.16.123.0 (summary Network Number)
> Advertising Router: 7.7.7.7
> LS Seq Number: 80000001
> Checksum: 0xF322
> Length: 28
> Network Mask: /24
> TOS: 0 Metric: 11175
>
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