From: gladston@br.ibm.com
Date: Wed Dec 22 2004 - 10:52:41 GMT-3
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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