11 Replies Latest reply: Apr 16, 2012 6:32 PM by Keith Barker - CCIE RS/Security, CISSP RSS

    OSPF over NBMA- FRS3 Configuration

    aneja_swati

      I am following CBT nuggets lab for OSPF over NBMA (using GNS3). I am stuck with configuration of FRS3 (router acting as FR switch).

      Can someone tell me

      1. how to configure FRS3 if AREA 356 is hybrid configuration (point-to-point and multipoint).

      2. Why the sub-interface modes for ARea 356 are like shown in 2nd diagram. Please explain in detail as it's v confusing. How its is hybrid and how routing is taking place.

       

      I have attached the diagrams. 2nd diagram shows the sub-int modes.

      Objectives

      Configure OSPF for the above network diagram. You will need to configure OSPF for the Area 0 and Area 24 Frame Relay network using the default OSPF network mode (no ip ospf network statements may be used on any router in these areas). R3′s interface connecting to Area 356 needs to be configures for the OSPF RFC standard point-to-multipoint mode. R5 and R6 must use the default OSPF mode (no ip ospf network statements may be used on R5 or R6).

      Each OSPF router has a single loopback interface. These should be advertised through the OSPF network. The loopback interfaces of the ABRs can be included in either area.

      Ensure only appropriate routers have DR/BDR status.

      In order to achieve full connectivity, you may need to add additional Frame-Relay maps to your routers. However, you may not add additional Frame-Relay PVCs by modifying the FRS devices.

      To test your configuration, R4 should be able to ping the loopback interfaces of R5 (5.5.5.5) and R6 (6.6.6.6).

       

      The way i configured FRS1 and 2 :

       

      FRS1#

       

      frame-relay switching

       

      interface Serial0/0

      no ip address

      encapsulation frame-relay

      clock rate 2000000

      frame-relay lmi-type ansi

      frame-relay intf-type dce

      frame-relay route 102 interface Serial0/1 201

      frame-relay route 103 interface Serial0/2 301

       

      interface Serial0/1

      no ip address

      encapsulation frame-relay

      clock rate 2000000

      frame-relay lmi-type ansi

      frame-relay intf-type dce

      frame-relay route 201 interface Serial0/0 102

       

      interface Serial0/2

      no ip address

      encapsulation frame-relay

      clock rate 2000000

      frame-relay lmi-type ansi

      frame-relay intf-type dce

      frame-relay route 301 interface Serial0/0 103

       

       

      FRS2#

       

      frame-relay switching

       

      interface Serial0/0

      no ip address

      encapsulation frame-relay

      clock rate 2000000

      frame-relay intf-type dce

      frame-relay route 204 interface Serial0/1 402

       

      interface Serial0/1

      no ip address

      encapsulation frame-relay

      clock rate 2000000

      frame-relay intf-type dce

      frame-relay route 402 interface Serial0/0 204

        • 1. Re: OSPF over NBMA- FRS3 Configuration
          Keith Barker - CCIE RS/Security, CISSP

          The frame switch is just providing PVCs with 2 ends each. 

           

          You could create a full mesh of PVCs for area 356, and then use those PVCs any way you want to (based on the configuration of the edge routers).

           

          FRS3#

           

          frame-relay switching

           

          interface Serial0/0

          no ip address

          encapsulation frame-relay

          clock rate 2000000

          frame-relay intf-type dce

          frame-relay route 305 interface Serial0/1 503

          frame-relay route 306 interface Serial0/2 603

           

          interface Serial0/1

          no ip address

          encapsulation frame-relay

          clock rate 2000000

          frame-relay intf-type dce

          frame-relay route 506 interface Serial0/2 605

           

          interface Serial0/2

          no ip address

          encapsulation frame-relay

          clock rate 2000000

          frame-relay intf-type dce

           

           

          3 PVCs would be a full mesh between RR3, R5 adn R6.

           

          You don't need to define the PVCs more than once.   (same PVC on 2 different interfaces)  

           

          The method you are using for the PVCs is the older method. 

           

          The cleaner newer method is shown in this video I created a while back:

           

           

          Best wishes,

           

          Keith

                     

          • 2. Re: OSPF over NBMA- FRS3 Configuration
            aneja_swati

            Thanks for your reply keith!

             

            So if I go by old method (I will switch to new one once I successfully finish old one which i already started); please correct me if i am wrong-

            - I don't need "route" statements on s0/1 and s0/2 on FRS1. Also, on FRS2, i don't need 'route' statement on s0/1.

            - For FRS3,  why did you configure this statement- s0/1 frame-relay route 506 interface Serial0/2 605 ???

            - So even if area 356 is hybrid, FRS3 is not differently configured than FRS1?

            • 3. Re: OSPF over NBMA- FRS3 Configuration
              Keith Barker - CCIE RS/Security, CISSP

              Hello-

               

              The configuration for the "hybrid" area, was simply a full mesh of PVCs between the 3 routers.  n(n-1)/2  or 3(3-1)/2 = 3 PVCs needed.

               

              You are correct, on FRS2 you don't need the redundant route statement on s0/1.

               

              For a full mesh, I added a PVC between R5 and R6, as I wasn't sure how you were going to configure the peering in that area.   If you don't need that PVC, don't add it to the frame switch config.

               

              Regarding FRS3, it is just like FRS1 in that all it knows is how to serve up L2 PVCs that go between 2 endpoints.   So yes, the same PVCs could be used (assuming the ones you need are in place) could be used to configure point to point, or point to multipoint, or any combination.

               

              I think you will enjoy this video.  It is on troubleshooting, but uses most of implementation options for frame relay, including physical interface, sub interfaces, point to point and point to multipoint.

               

               

              If you have other questions, let us know.

               

              Best wishes,

               

              Keith

              • 4. Re: OSPF over NBMA- FRS3 Configuration
                aneja_swati

                Thank you for the answers! And the video is very informative. I will try the configuration and get back with questions in case i get stumbled again!

                 

                Thanks!!!

                • 5. Re: OSPF over NBMA- FRS3 Configuration
                  aneja_swati

                  Keith,

                   

                  One thing that is bothering me here is that in Area 356, we have one network 10.35.6.0/24. Then how can we have 2 type of interfaces-. multipoint and point-to-point? Also for multipoint interface in this area(R3-S0/1), the objective is to apply command "ip ospf network point-to-multipoint". I didn't get it ??

                  • 6. Re: OSPF over NBMA- FRS3 Configuration
                    Keith Barker - CCIE RS/Security, CISSP

                    Hi-

                     

                    From the objectives, it says this:

                     

                    R5 and R6 must use the default OSPF mode (no ip ospf network statements may be used on R5 or R6).

                     

                    I don't know the exact reason for that objective of the vendor in this example, but putting that aside for a moment, here are some details regarding OSPF on frame relay:

                     

                    For two OSPF devices to form a neighborship, these parameters need to be agreeable:

                     

                    • Whether or not to use a DR (this relates to point2point, point to multipoint (both of which don't use a DR), or some flavor of broadcast which does use a DR.)
                    • Timers matching
                    • Network address, including correct mask length matching
                    • Flags (area type, authentication) matching
                    • Authentication secrets, if configured, matching

                     

                    There are a few more, but those are the critical ones.

                     

                    If you set the spokes up as p2p, the default hello will be 10 seconds.

                    If you set up the hub at p2multipoint, the default hello will be 30 seconds.

                     

                    In short, if you want this (interesting) configuration to work with those OSPF network types, you would have to manually go into the hub (R3) interface, and set the hello timer to 10, and then it would match the spokes, and they would become neighbors.

                     

                    With that in place, the LSAs would be flooded in the area, and there would be full connectivity between the 3 and any routes they are advertising in OSPF.

                     

                    Cheers,

                     

                    Keith.

                    • 7. Re: OSPF over NBMA- FRS3 Configuration
                      aneja_swati

                      Thanks for the explanation!

                      Let me try to explain my question once again. Please refer to the attachment (sub interface modes).

                       

                      1) If CBT nuggets want such a scenario as seen in diagram (and objectives), then shouldn't R5, R6 and R3's interfaces belonging to area 356 be in different subnets? I mean, how can r3's multipoint subinterface be in same subnet as R5 and R6's p-t-p interface?

                      2) Also why did we configure R3's s0/1 interface as multipoint and then go under it and configure network type as point-to -multipoint? What's the idea behind it?

                      R3# interface Serial0/0.1 multipoint

                        ip address 10.12.3.3 255.255.255.0

                        ip ospf network point-to-multipoint

                       

                      Thanks again for your time!

                      • 8. Re: OSPF over NBMA- FRS3 Configuration
                        Keith Barker - CCIE RS/Security, CISSP

                        learner wrote:

                         

                        Thanks for the explanation!

                        Let me try to explain my question once again. Please refer to the attachment (sub interface modes).

                         

                        1) If CBT nuggets want such a scenario as seen in diagram (and objectives), then shouldn't R5, R6 and R3's interfaces belonging to area 356 be in different subnets? I mean, how can r3's multipoint subinterface be in same subnet as R5 and R6's p-t-p interface?

                        2) Also why did we configure R3's s0/1 interface as multipoint and then go under it and configure network type as point-to -multipoint? What's the idea behind it?

                        R3# interface Serial0/0.1 multipoint

                          ip address 10.12.3.3 255.255.255.0

                          ip ospf network point-to-multipoint

                         

                        Thanks again for your time!

                         

                        Hi-

                         

                        Regarding #1, not sure what they were trying to accomplish.  You may want to ask them that question. 

                         

                        1.  As I previously mentioned, R3 could have a multipoint interface, and both R5/R6 could have p-t-p interfaces (all related to OSPF network types which don't require a DR on the subnet), and if that were the case and all 3 had compatible IP addresses (meaning from the same subnet), then that would work.

                         

                        2. Default physical interface type on serial interface is looking for a DR (broadcast type, ospf).   By saying R3 was a point to multipoint, it gets rid of the requirement for a DR, similar to p-2-p.    Adjusting the timers would allow neighbors of these similar non-dr types to become neighbors.

                         

                        I don't know the full objective of their exercise, but it appears to have provided you a good platform for discovery.

                         

                        Best wishes,

                         

                        Keith

                        • 9. Re: OSPF over NBMA- FRS3 Configuration
                          aneja_swati

                          Objectives for this lab were:

                          Objectives

                          Configure OSPF for the above network diagram. You will need to configure OSPF for the Area 0 and Area 24 Frame Relay network using the default OSPF network mode (no ip ospf network statements may be used on any router in these areas). R3′s interface connecting to Area 356 needs to be configures for the OSPF RFC standard point-to-multipoint mode. R5 and R6 must use the default OSPF mode (no ip ospf network statements may be used on R5 or R6).

                          Each OSPF router has a single loopback interface. These should be advertised through the OSPF network. The loopback interfaces of the ABRs can be included in either area.

                          Ensure only appropriate routers have DR/BDR status.

                          In order to achieve full connectivity, you may need to add additional Frame-Relay maps to your routers. However, you may not add additional Frame-Relay PVCs by modifying the FRS devices.

                          To test your configuration, R4 should be able to ping the loopback interfaces of R5 (5.5.5.5) and R6 (6.6.6.6).

                          • 10. Re: OSPF over NBMA- FRS3 Configuration
                            aneja_swati

                            Thanks a lot! I got your second point clearly. Just having all interfaces in same subnet is still a question. I will try to read some documentation on this.

                             

                            Thanks again!!

                            Swati

                            • 11. Re: OSPF over NBMA- FRS3 Configuration
                              Keith Barker - CCIE RS/Security, CISSP

                              You are welcome Swati-

                               

                              Best wishes,

                               

                              Keith.