Re: OSPF routing through 2 ways

Jan Rolny · ‎05-04-2011

Hi all,

please see picture attached. This is my topology and I would like to simulate two independent circuits with OSPF routing. Primary routing path should go thru SW1 and in case that SW1 will fail (for example power off) so OSPF should find second path via switch SW2.

I have configured 2 OSPF processes and two OSPF areas. Please see config below. Seems that everything works fine but path selection is based on

bandwith and other things. So now OSPF decided to route partly via SW1 and partly via SW2. I would like to force OSPF to route everything via

SW1 and in case of failure to SW2. Is it possible ? Is diagram below nonsense?

R2

!
router ospf 1
log-adjacency-changes
network 10.252.1.0 0.0.0.255 area 1
network 192.168.5.0 0.0.0.255 area 1
!
router ospf 2
log-adjacency-changes
network 10.252.2.0 0.0.0.255 area 2
network 192.168.5.0 0.0.0.255 area 2
!
==========================

R3

!
router ospf 1
log-adjacency-changes
network 10.252.1.0 0.0.0.255 area 1
network 192.168.4.0 0.0.0.255 area 1
!
router ospf 2
log-adjacency-changes
network 10.252.2.0 0.0.0.255 area 2
network 192.168.4.0 0.0.0.255 area 2

===============================

R4

!
router ospf 1
log-adjacency-changes
network 10.252.1.0 0.0.0.255 area 1
network 192.168.3.0 0.0.0.255 area 1
!
router ospf 2
log-adjacency-changes
network 10.252.2.0 0.0.0.255 area 2
network 192.168.3.0 0.0.0.255 area 2

Thank you for tips,

Jan.

IAN WHITMORE · ‎05-04-2011

Seems that everything works fine but path selection is based on bandwith and other things.

You can change the bandwidth settings so that it prefers the links to switch one by making them "faster" or making the links to switch 2 "slower" (at least at the configuration level). You can also change other things like cost.

Is diagram below nonsense?

Depends. Is this just a test lab or for some other function? Why do you need the traffic to go over sw1 specifically?

Of course I don't think you need two OSPF processes. OSPF will autmotically use the back-up links if available. Again, if you just use one process and make the links to switch2 "slower" then it should always use switch1 unless switch1 fails. Of course that could affect your monitoring tools if you are monitoring the bandwidth of the interfaces. You could also try changing the cost.

Here is a great Q&A sheet from Cisco that covers all this:

http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a0080094704.shtml#q37

HTH,

Ian

Jan Rolny · ‎05-04-2011

Hi Ian,

thanks for answer. I would prefer to change cost of the link, because speed will be probably same. Regarding SW1, it simulate primary circuit (in real it will be MPLS) and SW2 simulate SDH technology.

So it is requirement from customer to use MPLS as primary circuit for communication.

Jan.