9 Replies Latest reply: Nov 7, 2018 9:50 AM by Learner RSS

    OSPFv3 Passive interface

    Learner

      Hello all,

       

      From page 625, Chap 23, ICND2 OCG, this is the OSPFv3 configuration on a router.

       

      Why does it enable OSPFv3 on interface g0/1, but then made the interface passive with "Passive-interface g0/1"? 

       

       

      ospfv3.jpg

        • 1. Re: OSPFv3 Passive interface
          Ing_Percy

          Hi!

           

          Maybe because this interface connects to LAN network

          What is the topology?

           

          Best regards!

          • 2. Re: OSPFv3 Passive interface
            Martin

            could be a typo; if u have errata, check it

            or  could be just an example use to show 2 items

            • 3. Re: OSPFv3 Passive interface
              Steven Davidson

              With "ipv6 router ospf" or "router ospfv3 " you cannot add networks using the "network x.x.x.x area y" statement like you can for OSPFv2.  You have to enable ospfv3 under the interface configuration.  If you do not want neighbors to form on that interface but you want the prefix associated with the interface added into the LSDB then you want to make the interface passive and that's done under the router process (both in OSPFv2 and v3).

              • 4. Re: OSPFv3 Passive interface
                Ing_Percy

                Hi!

                 

                A lab in GNS3

                 

                ospv3.JPG

                R1#sh run int f0/0

                interface FastEthernet0/0

                no ip address

                duplex auto

                speed auto

                ipv6 address 2001:DB8:1:14::1/64

                ipv6 ospf 1 area 0

                end

                 

                R1#sh run int f0/1

                interface FastEthernet0/1

                no ip address

                duplex auto

                speed auto

                ipv6 address 2001:DB8:1:4::1/64

                ipv6 ospf 1 area 0

                end

                 

                R1#sh run | sec ipv6 router

                ipv6 router ospf 1

                router-id 1.1.1.1

                log-adjacency-changes

                passive-interface FastEthernet0/1

                 

                R2#sh run int f0/0

                interface FastEthernet0/0

                no ip address

                duplex auto

                speed auto

                ipv6 address 2001:DB8:1:14::2/64

                ipv6 ospf 1 area 0

                end

                 

                R2#sh run | sec ipv6 router

                ipv6 router ospf 1

                router-id 2.2.2.2

                log-adjacency-changes

                 

                R2#sh ipv6 route ospf

                IPv6 Routing Table - 5 entries

                Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP

                      U - Per-user Static route

                      I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary

                      O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2

                      ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2

                O  2001:DB8:1:4::/64 [110/20]

                    via FE80::C201:11FF:FE28:0, FastEthernet0/0


                Best regards!

                • 5. Re: OSPFv3 Passive interface
                  Mustafa

                  Per diagram Figure 23-5  "Area Design for the Multiarea OSPFv3 Example" on pg.623 the router R4 interface Gi 0/1 is facing to LAN, so per book they need to enable OSPFv3 on that network but they don't want to send any hello messages because there are not any other routers on that segment.

                  • 6. Re: OSPFv3 Passive interface
                    Learner

                    I see. It's to advertise the LAN network on that interface but disable OSPF hello packets since there is no reachable OSPF neighbor on that interface.

                    • 7. Re: OSPFv3 Passive interface
                      Learner

                      Below is the network topology from the book.

                       

                      The book shows only R4 has the passive-interface command on its g0/1 interface. I understand R4 needs it since there is no other OSPF routers connected to the interface. But why not also run the passive-interface command on R1's G0/0.11 and G0/0.12? I can see R1 should form OSPF neighbors with itself through these two interfaces. But what's the point in doing that?

                       

                      What about R2's G0/0 and R3's G0/0? R2 and R3 would form OSPF neighbors through these two interfaces. But they are already neighbors through R1. Is it having two links better than one?

                       

                       

                       

                      ospfv3-2.jpg

                      • 8. Re: OSPFv3 Passive interface
                        Mustafa

                        "What about R2's G0/0 and R3's G0/0? R2 and R3 would form OSPF neighbors through these two interfaces. But they are already neighbors through R1. Is it having two links better than one?"

                        Think about this what will happen if the link s0/0/1 on R2 is failed and you don't have OSPF neighborship. Will R2 know how to get out (if we don't have static routes)?

                         

                        "But why not also run the passive-interface command on R1's G0/0.11 and G0/0.12?"

                        Yes, you can configure these interfaces as passive. Pg. 205 Example8-10. R1 cannot make itself as neighbor, special through these interfaces, it is physical one but logical two independent interfaces.

                        • 9. Re: OSPFv3 Passive interface
                          Learner

                          "What about R2's G0/0 and R3's G0/0? R2 and R3 would form OSPF neighbors through these two interfaces. But they are already neighbors through R1. Is it having two links better than one?"

                          Think about this what will happen if the link s0/0/1 on R2 is failed and you don't have OSPF neighborship. Will R2 know how to get out (if we don't have static routes)?

                           

                          I see. It can function as a backup link.