Interconnecting 2 sites

[WBNetAdmin]

I want to interconnect 2 sites through dark fiber using L3 connectivity. Currently the 2 sites are connected through ISP L3 MPLS.The 2 sites have Core switches redistributing static routes into OSPF routing protocol and then get redistributed into the ISP MPLS WAN network.I want to make the Dark fiber as the primary path and the MPLS WAN as the secondary path for only certain subnets.How can this be best achieved in terms of routing?

[Richard Burts]

You have not given much detail so our understanding of your situation and your requirements is limited. But based on what we know so far I would suggest that if you run OSPF on the fiber between the sites then OSPF will learn and advertise the site prefixes as OSPF internal routes. The MPLS routes are redistributed so they are OSPF external prefixes. OSPF always prefers an internal route over an external route. So your fiber will be primary and MPLS would be secondary.

HTH

Rick

[WBNetAdmin]

Thank you Rick for taking the time out for answering my query. Actually I would like to use the Dark Fiber only as a point to point link between the core switches of the 2 sites and not run any routing protocol over it. I would like to route only a couple of subnets over this fiber as a primary path and use the ISP WAN network as a secondary path.

We have some static routes which are defined on the core switch. These static routes are then redesitributed into our WAN network through OSPF and then redistributed into the ISP network through BGP protocol.

Now If we define a static route to a remote subnet on the core switch to go over the Fiber as the primary path and redistribute to the WAN network and to the ISP network as a secondary path, how best can I achieve this? I reckon that when the route goes over the fiber, it should not redistribute into the WAN cloud network and only when the fiber is unavailable, it will install the in the routing table of the core and get redistributed through the ISP path.

Your expert advice is much appreciated.

Thanks again

[Richard Burts · Accepted solution]

Thanks for clarifying what you are trying to achieve. Based on this further information I have a couple of ideas that you might consider.

One alternative is to configure a second instance of OSPF which would run over the dark fiber and would advertise only the subnets that you want to go over the fiber. You could then configure floating static routes for those subnets to go over the ISP network and redistribute the floating static into the main instance of OSPF. I like the use of a routing protocol over the dark fiber because that will automatically detect if there is a problem and you have lost connectivity over the fiber.

If you do not want to run a dynamic routing protocol over the fiber then you could configure static routes to direct the subnets that you want over the fiber. You could then configure IP SLA to track the static routes over the fiber and withdraw the routes if the fiber has a problem. And you could configure floating static to send the subnets over the ISP network if the primary static is withdrawn.

HTH

Rick

[WBNetAdmin]

Thank you Rick. I reckon that the 2 solutions you have provided are very practical. I think I will consider the first solution and look into it further. I may need to contact you in case I encounter some obstacles if it's ok with you.

Thanks a ton once again.

Ryan

[Richard Burts]

Ryan

I am glad that my suggestions are helpful. Thank you for using the ratings system to mark this question as answered. go ahead with the implementation and if you encounter obstacles feel free to get in touch. 

HTH

Rick