OSPF cost behaviour

Dear GS,

I'm trying to figure out why manipulating interface OSPF cost does't
change the path to get to a network on a scenario like this:

172.30.0.0/20
R3
/B B B B B B \
R1 --- R2

R1-R3 - Area 10
R2-R3 - Area 10
R1-R2 - Area 0

Increasing OSPF cost on path R2->R3 should't R2 prefer R1 to get to
172.30.0.0/20 ?

R2#show ip route 172.30.0.0
Routing entry for 172.30.0.0/20, 1 known subnets

O E1B B B 172.30.0.0 [110/30] via 172.29.4.33, 00:00:01, Ethernet0/1

After changing Cost to 1000, R2 still prefers same path, even with a
higher cost:

R2#conf t
Enter configuration commands, one per line.B End with CNTL/Z.
R2(config)#int et 0/1
R2(config-if)#ip ospf cost 1000
R2(config-if)#^Z
R2#show ip route 172.30.0.0
Routing entry for 172.30.0.0/20, 1 known subnets

O E1B B B 172.30.0.0 [110/1020] via 172.29.4.33 , 00:00:10,
Ethernet0/1B B <<<<----- still prefers same path
R2#

B

I noticed route through R1 is not on LSDB (maybe it is the same ?):

R2#show ip ospf database | b Type-5
Type-5 AS External Link States

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum Tag
172.30.0.0B B B B B 172.30.0.1B B B B B 342B B B B B B B B 0x80000002
0x00DFB8 0
R2#

B

But if R2 loose path to R3, it works:

R2#conf t
R2(config)#int et 0/1
R2(config-if)#shutdown
R2(config-if)#^Z
R2#show ip route 172.30.0.0
Routing entry for 172.30.0.0/20, 1 known subnets

O E1B B B 172.30.0.0 [110/40] via 192.168.1.62, 00:00:04, Ethernet0/0B
<<<-----

R2#show ip ospf database | b Type-5
Type-5 AS External Link States

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum Tag
172.30.0.0B B B B B 172.30.0.1B B B B B 599B B B B B B B B 0x80000002
0x00DFB8 0
R2#

Since this is my first post, hope it's not too long and not a dumb issue
:)

Kindest Regards,

---- checks ----

R2#show ip ospf database

OSPF Router with ID (192.168.1.61) (Process ID 1)

Router Link States (Area 0)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum Link count
192.168.1.61B B B 192.168.1.61B B B 1323B B B B B B B 0x80000007
0x007A09 1
192.168.1.62B B B 192.168.1.62B B B 1870B B B B B B B 0x80000003
0x008004 1

Net Link States (Area 0)

Link IDB B B B B B B B ADV Rout erB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum
192.168.1.62B B B 192.168.1.62B B B 1871B B B B B B B 0x80000001
0x002A7D

Summary Net Link States (Area 0)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum
172.29.4.32B B B B 192.168.1.61B B B 153B B B B B B B B 0x80000006
0x00477E
172.29.4.32B B B B 192.168.1.62B B B 1304B B B B B B B 0x8000000B
0x00712F
172.29.4.48B B B B 192.168.1.61B B B 153B B B B B B B B 0x80000004
0x00B402
172.29.4.48B B B B 192.168.1.62B B B 1823B B B B B B B 0x80000003
0x00D6C2

Summary ASB Link States (Area 0)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum
172.30.0.1B B B B B 192.168.1.61B B B 153B B B B B B B B 0x80000004
0x00EEEA
172.30.0.1B B B B B 192.168.1.62B B B 1608B B B B B B B 0x80000001
0x001F9E

Router Link States (Area 10)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum Link count
172.30.0.1B B B B B 172.30.0.1B B B B B 1317B B B B B B B 0x80000008
0x00A8F8 2
192.168.1.61B B B 192.168.1.61B B B 159B B B B B B B B 0x8000000B
0x00DC2E 1
192.168.1.62B B B 192.168.1.62B B B 1833B B B B B B B 0x80000002
0x00B31B 1

Net Link States (Area 10)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum
172.29.4.33B B B B 172.30.0.1B B B B B 1313B B B B B B B 0x80000003
0x00E830
172.29.4.54B B B B 192.168.1.62B B B 1833B B B B B B B 0x80000001
0x0035F2

Summary Net Link States (Area 10)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum
192.168.1.48B B B 192.168.1.61B B B 1317B B B B B B B 0x80000005
0x006A91
192.168.1.48B B B 192.168.1.62B B B 1862B B B B B B B 0x80000003
0x006894
Type-5 AS External Link States

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum Tag
172.30.0.0B B B B B 172.30.0.1B B B B B 1590B B B B B B B 0x80000001
0x00E1B7 0
R2#

---------------

R1#show ip ospf database

OSPF Router with ID (192.168.1.62) (Process ID 1)

Router Link States (Area 0)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum Link count
192.168.1.61B B B 192.168.1.61B B B 1393B B B B B B B 0x80000007
0x007A09 1
192.168.1.62B B B 192.168.1.62B B B 16B B B B B B B B B 0x80000004
0x007E05 1

Net Link States (Area 0)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum
192.168.1.62B B B 192.168.1.62B B B 16B B B B B B B B B 0x80000002
0x00287E

Summary Net Link States (Area 0)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum
172.29.4.32B B B B 192.168.1.61B B B 224B B B B B B B B 0x80000006
0x00477E
172.29.4.32B B B B 192.168.1.62B B B 1372B B B B B B B 0x8000000B
0x00712F
172.29.4.48B B B B 192.168.1.61B B B 224B B B B B B B B 0x80000004
0x00B402
172.29.4.48B B B B 192.168.1.62B B B 16B B B B B B B B B 0x80000004
0x00D4C3

Summary ASB Link States (Area 0)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum
172.30.0.1B B B B B 192.168.1.61B B B 224B B B B B B B B 0x80000004
0x00EEEA
172.30.0.1B B B B B 192.168.1.62B B B 1677B B B B B B B 0x80000001
0x001F9E

Router Link States (Area 10)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum Link count
172.30.0.1B B B B B 172.30.0.1B B B B B 1388B B B B B B B 0x80000008
0x00A8F8 2
192.168.1.61B B B 192.168.1.61B B B 231B B B B B B B B 0x8000000B
0x00DC2E 1
192.168.1.62B B B 192.168.1.62B B B 17B B B B B B B B B 0x80000003
0x00B11C 1

Net Link States (Area 10)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum
172.29.4.33B B B B 172.30.0.1B B B B B 1383B B B B B B B 0x80000003
0x00E830
172.29.4.54B B B B 192.168.1.62B B B 17B B B B B B B B B 0x80000002
0x0033F3

Summary Net Link States (Area 10)

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum
192.168.1.48B B B 192.168.1.61B B B 1389B B B B B B B 0x80000005
0x006A91
192.168.1.48B B B 192.168.1.62B B B 17B B B B B B B B B 0x80000004
0x006695

Type-5 AS External Link States

Link IDB B B B B B B B ADV RouterB B B B B AgeB B B B B B B B
Seq#B B B B B B Checksum Tag
172.30.0.0B B B B B 172.30.0.1B B B B B 1660B B B B B B B 0x80000001
0x00E1B7 0
R1#

------ confs -----

R1#
router ospf 1
log-adjacency-changes
network 172.29.4.54 0.0.0.0 area 10
network 192.168.1.62 0.0.0.0 area 0

interface Ethernet0/1
ip address 172.29.4.54 255.255.255.240
full-duplex
end

R2#
router ospf 1
log-adjacency-changes
network 172.29.4.38 0.0.0.0 area 10
network 192.168.1.61 0.0.0.0 area 0

interface Ethernet0/1
ip address 172.29.4.38 255.255.255.240
ip ospf cost 1000
full-duplex
end

R3#
interface FastEthernet1/1
no switchport
ip address 172.29.4.49 255.255.255.240
end

interface FastEthernet1/2
no switchport
ip address 172.29.4.33 255.255.255.240
duplex full
end

!
interface Loopback0
ip address 172.30.0.1 255.255.240.0
end

router o spf 1
log-adjacency-changes
redistribute connected metric-type 1 subnets route-map CONN->OSPF
network 172.29.4.33 0.0.0.0 area 10
network 172.29.4.49 0.0.0.0 area 10

route-map CONN->OSPF permit 10
match interface Loopback0

B

B

Fernando Sete Garcia

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Received on Tue Jul 14 2009 - 21:47:29 ART