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New Member

OSPF: specifying cost

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!

2 ACCEPTED SOLUTIONS

Accepted Solutions
VIP Super Bronze

OSPF: specifying cost

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

Hall of Fame Super Silver

OSPF: specifying cost

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

9 REPLIES
VIP Super Bronze

OSPF: specifying cost

you can change the cost on router A, under the interface. the command is

ip os cost xx

HTH

New Member

OSPF: specifying cost

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!

VIP Super Bronze

OSPF: specifying cost

Ok, sorry. I misunderstood you. So  you are trying to use the same outgoing interface but different cost per subnet right?

New Member

OSPF: specifying cost

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.

OSPF: specifying cost


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

VIP Super Bronze

OSPF: specifying cost

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

New Member

OSPF: specifying cost

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.

VIP Super Bronze

OSPF: specifying cost

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

Hall of Fame Super Silver

OSPF: specifying cost

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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