Hi All,
Please advise on the below. I am just understanding the cost calculations. Consider the link between R2 and R3.
R2 has loopback 2.2.2.2 in area 0
R4 has loopback 4.4.4.4 in area 0
I have changed the cost of R4 (Eth 1/1) as 200.
From below
R2#sh ip ospf database router self-originate
Link connected to: a Stub Network
(Link ID) Network/subnet number: 2.2.2.2
(Link Data) Network Mask: 255.255.255.255
Number of MTID metrics: 0
TOS 0 Metrics: 1
Link connected to: a Virtual Link
(Link ID) Neighboring Router ID: 1.1.1.1
(Link Data) Router Interface address: 10.1.1.2
Number of MTID metrics: 0
TOS 0 Metrics: 10
Link connected to: a Transit Network
(Link ID) Designated Router address: 172.16.1.2
(Link Data) Router Interface address: 172.16.1.2
Number of MTID metrics: 0
TOS 0 Metrics: 10
So R2 is adjacent with DR( Considering as a Virtual Process) and the cost to reach the DR is 10.
Checking what is the DR adjacent with we have,
R2#sh ip ospf database network 172.16.1.2
OSPF Router with ID (2.2.2.2) (Process ID 1)
Net Link States (Area 0)
Routing Bit Set on this LSA in topology Base with MTID 0
LS age: 776
Options: (No TOS-capability, DC)
LS Type: Network Links
Link State ID: 172.16.1.2 (address of Designated Router)
Advertising Router: 2.2.2.2
LS Seq Number: 80000001
Checksum: 0xCB8E
Length: 32
Network Mask: /24
Attached Router: 2.2.2.2
Attached Router: 4.4.4.4
So it has a router 4.4.4.4 attached to the link. So cost from 2.2.2.2 to reach the node with link identifier is cost 10 from above.
So from r2#sh ip route 4.4.4.4 (10 + 1(for r4 to loopback))=11
R2#sh ip route 4.4.4.4
Routing entry for 4.4.4.4/32
Known via "ospf 1", distance 110, metric 11, type intra area
Last update from 172.16.1.4 on Ethernet1/1, 00:19:44 ago
Routing Descriptor Blocks:
* 172.16.1.4, from 4.4.4.4, 00:19:44 ago, via Ethernet1/1
Route metric is 11, traffic share count is 1
Now Taking from R4#
Router Link States (Area 0)
LS age: 922
Options: (No TOS-capability, DC)
LS Type: Router Links
Link State ID: 4.4.4.4
Advertising Router: 4.4.4.4
LS Seq Number: 80000005
Checksum: 0x8A25
Length: 60
Number of Links: 3
Link connected to: a Stub Network
(Link ID) Network/subnet number: 4.4.4.4
(Link Data) Network Mask: 255.255.255.255
Number of MTID metrics: 0
TOS 0 Metrics: 1
Link connected to: a Transit Network
(Link ID) Designated Router address: 192.168.1.3
(Link Data) Router Interface address: 192.168.1.4
Number of MTID metrics: 0
TOS 0 Metrics: 10
Link connected to: a Transit Network
(Link ID) Designated Router address: 172.16.1.2
(Link Data) Router Interface address: 172.16.1.4
Number of MTID metrics: 0
TOS 0 Metrics: 200
R4#sh ip ospf database network 172.16.1.2
OSPF Router with ID (4.4.4.4) (Process ID 1)
Net Link States (Area 0)
Routing Bit Set on this LSA in topology Base with MTID 0
LS age: 1263
Options: (No TOS-capability, DC)
LS Type: Network Links
Link State ID: 172.16.1.2 (address of Designated Router)
Advertising Router: 2.2.2.2
LS Seq Number: 80000001
Checksum: 0xCB8E
Length: 32
Network Mask: /24
Attached Router: 2.2.2.2
Attached Router: 4.4.4.4
Now the metric is 201
R4#sh ip route 2.2.2.2
Routing entry for 2.2.2.2/32
Known via "ospf 1", distance 110, metric 201, type intra area
Last update from 172.16.1.2 on Ethernet1/1, 00:25:10 ago
Routing Descriptor Blocks:
* 172.16.1.2, from 2.2.2.2, 00:25:10 ago, via Ethernet1/1
Route metric is 201, traffic share count is 1
Not sure if I understand correctly, but if they are adjacent to the DR, how can the cost differ? I mean if I have changed to cost on interface eth 1/1, should it not be reflected in R2#sh ip ospf database router self-originate?? Please kindly advise.
Thanks
