7 Replies Latest reply: May 10, 2012 1:07 AM by Mike Gannon RSS

    OSPF to static routes


      I am moving from an OSPF routing to a static routing between 2 sites. There are two links between the 2 sites. The primary is a 10mb fiber link pt-to-pt connection. The secondary link is the backup link via MPLS. The MPLS is an ethernet hand-off from the ISP.


      My other site is in Canada. My plan is to add the static routes on top of OSPF, then remove the network on OSPF 1-by-1. Will it work? As the static routes AD is lower than OSPF so the traffic will take the static routing. Correct?


      My concern is if I remove the OSPF and the static routing somehow does not work, then I cannot telnet back to the router. Any thoughts? Thx

        • 1. Re: OSPF to static routes
          Bradford Chatterjee (CCIEx2/CCDE)

          You can make this work by setting the administrative distance of the static routes to be greater than 110 when you initially enter them. You can set the AD of a static route by simply adding a number to the end of the "ip route" statement such as "ip route 254" where 254 is the administrative distance.


          There are at least three ways to attempt to remove the OSPF without worrying about your remote access. The first and easiest is simply to make certain that you can telnet across your point-to-point link from the near router to the far router. You don't need OSPF for that, but your ACLs may not permit this. Second, you can remove OSPF from the near side first; if you lose access to the remote side then you can just put the OSPF config back on the router to which you still have access.


          Third, if you're feeling brave then you can save your config before you make your changes and issue the "reload in" command before you remove OSPF from the far router so that the router will automatically reload and revert to a working configuration if the new config fails. This could result in some extended downtime, however, and is not ideal.

          • 2. Re: OSPF to static routes

            I am making the presumption you have a good reason to do this, so I'll get straight to the question.


            My recommendation would be to add the static routes, a few at a time, and then monitor the environment and verify routing converges onto the lower AD-cost static routes. Then you can add the rest. 


            Once you see it all has converged, execute the removal of OSPF routes in a very similar fashion. Remove a route that does not impact connectivity to the device, and confirm routing is stable and still functional. Remove any routes that impact routing to the device last.


            With the removal of dynamic routing you will need static routes on both side to ensure that both sides of the network know how to get to eachother. My explanation is simply speaking from one side of the network.


            Ideally if you do not want to load balance across both links, you would use two static routes on the spoke. The normal static pointing out of the primary link and then you have a floating static pointing out of the secondary link.

            • 3. Re: OSPF to static routes

              Not sure why you need to add an AD higher than 110. Don't you want to set the AD lower than 110 so that all the routes prefer the static routes? Thx

              • 4. Re: OSPF to static routes


                I do not load balance between the two link. One link is the primary and the other is the secondary. I plan in using IP SLA for the failover between the two static routes, one pointing to the primary and the other pointing to the secondary. Thx

                • 5. Re: OSPF to static routes
                  Bradford Chatterjee (CCIEx2/CCDE)

                  If you want to install the static routes without interrupting your OSPF environment then you can do it in that way. Then the static routes take over only when you remove OSPF.

                  • 6. Re: OSPF to static routes

                    I see. Thx

                    • 7. Re: OSPF to static routes
                      Mike Gannon

                      I agree with Biggy Biggy,


                      Install static routes with lower AD than OSPF

                      Everytime you enter a new static route you will see your OSPF route drop from the RIB. Once there are no more OSPF routes in RIB go ahead and disable OSPF.


                      no risk at all asd long as you check with sh ip route before disabling OSPF


                      Good luck