11-03-2011 02:44 PM - edited 03-07-2019 03:12 AM
Let's say I have a router A with OSPF and network 10.10.10.0/24 and 10.10.12.0/24 in area 0 to advertise. It has two interfaces connecting to
two other routers B and C also in area 0. Router A's connecting interfaces are fa0/1 (to B) and fa0/2 (to C). When router
B receives the 10.10.10.0 route I want the cost to be 10 and when it receives the 10.10.12.0 route I want the cost to be 100.
How can I color the route costs so that they are different despite being hear on the same interface? Thanks!
Solved! Go to Solution.
11-03-2011 03:15 PM
I don't think there is a way to do this running OSPF, because you can only manipulate the cost for the physical interface or vlan interface
11-03-2011 07:39 PM
OSPF is a link state protocol. And one of the basic principles of a link state protocol is that each router must have an accurate map of the topology of its network. This principle means that all locally connected routes that router A advertises to router B must have the same metric.
To achieve his requirements the original poster needs to look into a different routing protocol. He might achieve it with IBGP, but I think that a better choice would be to use EIGRP.
HTH
Rick
11-03-2011 03:03 PM
you can change the cost on router A, under the interface. the command is
ip os cost xx
HTH
11-03-2011 03:07 PM
But that would mean both network 10.10.10.0 and 10.10.12.0 would arrive at router B with cost xx. What I would like to do is have 10.10.10.0 arrive at B with cost with cost 10 and 10.10.12.0 arrive at B with cost 100. But both route advertisements would be egressing routing A on the same interface fa0/1. Thank you!
11-03-2011 03:10 PM
Ok, sorry. I misunderstood you. So you are trying to use the same outgoing interface but different cost per subnet right?
11-03-2011 03:14 PM
Yes - exactly. So in my example the interfaces on router A would be say:
fa0/0 - 10.10.78.1/24
fa0/1 - 10.10.79.1/24
fa1/0 - 10.10.10.1/24
fa1/1 - 10.10.12.1/24
ospf 1
router-id 1.1.1.1
network 10.10.10.0 0.0.0.255 area 0
network 10.10.12.0 0.0.0.255 area 0
So when these two networks 10.10.10.0 and 10.10.12.0 are advertised out fa0/0 and router B receives the routes, each route would have a different cost.
11-03-2011 05:13 PM
Yes - exactly. So in my example the interfaces on router A would be say:
fa0/0 - 10.10.78.1/24
fa0/1 - 10.10.79.1/24
fa1/0 - 10.10.10.1/24
fa1/1 - 10.10.12.1/24
ospf 1
router-id 1.1.1.1
network 10.10.10.0 0.0.0.255 area 0
network 10.10.12.0 0.0.0.255 area 0
So when these two networks 10.10.10.0 and 10.10.12.0 are advertised out fa0/0 and router B receives the routes, each route would have a different cost.
This is achievable by specifying the cost on the remote side physical interface. So, in your case lets say fa1/1 on Router A is connecting to Router Z. and network between them is 10.10.12.0/24. Then , you simply add the cost on the remote side physical interface to 90. So, now when the Router B sees the route it would see it as 10(cost of fast eth fa0/0 + 90(which we have changed on the Router Z).
Hope this helps,
Kishore
11-03-2011 03:15 PM
I don't think there is a way to do this running OSPF, because you can only manipulate the cost for the physical interface or vlan interface
11-03-2011 03:38 PM
Interesting. With BGP I know I can alter attributes as the routes are received on which routing decisions can be made. So I was assuming there would be something similar in OSPF. Perhaps for this situation iBGP would work better.
11-03-2011 03:08 PM
have a look. The original cost for this interface was 1 I changed it to 10
Switch#sh ip os in
Switch#sh ip os interface
Vlan1 is up, line protocol is up
Internet Address 192.168.1.10/24, Area 0
Process ID 1, Router ID 192.168.1.10, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State WAITING, Priority 1
No designated router on this network
No backup designated router on this network
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:03
Wait time before Designated router selection 00:00:33
Supports Link-local Signaling (LLS)
Cisco NSF helper support enabled
IETF NSF helper support enabled
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 0, maximum is 0
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
Switch#config t
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)#int
Switch(config)#interface gi
Switch(config)#interface gigabitEthernet 1/0/1
Switch(config-if)#ip os co
Switch(config-if)#ip os cos
Switch(config-if)#inter vlan 1
Switch(config-if)#ip os
Switch(config-if)#ip ospf co
Switch(config-if)#ip ospf cost 10
Switch(config-if)#do sh ip os int
Vlan1 is up, line protocol is up
Internet Address 192.168.1.10/24, Area 0
Process ID 1, Router ID 192.168.1.10, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 192.168.1.10, Interface address 192.168.1.10
No backup designated router on this network
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:01
Supports Link-local Signaling (LLS)
Cisco NSF helper support enabled
IETF NSF helper support enabled
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 0, maximum is 0
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
Switch(config-if)#
HTH
11-03-2011 07:39 PM
OSPF is a link state protocol. And one of the basic principles of a link state protocol is that each router must have an accurate map of the topology of its network. This principle means that all locally connected routes that router A advertises to router B must have the same metric.
To achieve his requirements the original poster needs to look into a different routing protocol. He might achieve it with IBGP, but I think that a better choice would be to use EIGRP.
HTH
Rick
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