7 Replies Latest reply: May 13, 2016 1:00 AM by Prakash RSS

    OSPF v3 vs OSPF v2


      Hi All,


      Can anybody share the correct difference between these two versions (Ospf V2 and Ospf V3). I knew ospf v3 could support ipv6 address, but when i read RFC 6969 and RFC 5838, It stated that OSPFv3 could run ipv4 and ipv6 address family. Is that correct by using Ospfv3 alone can we able to route ipv4 and ipv6 networks.



        • 1. Re: OSPF v3 vs OSPF v2
          Jon Major CCIE# 47884

          That is correct! It can exchange IPv4 routes, the only catch is that it does so using IPv6 transport for ospfv3 LSAs.

          • 2. Re: OSPF v3 vs OSPF v2

            Hi Jon,


            Thanks for the confirmation, Now that creates another query, which is about ISIS. When we compare ISIS vs OSPF, There is an advantage to run ISIS over OSPF that is ISIS  could run two different address families ipv4 and ipv6 on single instance but for ospf we have to run two different protocols two route ipv4 and ipv6, thats one of the reason large scale service providers are preferring ISIS over OSPF.

            So this thing is little bit confusing to me.



            • 3. Re: OSPF v3 vs OSPF v2
              Jon Major CCIE# 47884

              You can have single topology IS-IS, but that still requires every IPv4 link to have IPv6 addressing or you'll break forwarding with single top IS-IS.


              That said, IS-IS single topology would be a more efficient way to run IPv4 and IPv6. With OSPFv3, it's still a single process running IPv4 and IPv6, but we have two different topologies and we actually form neighbors for both address-families.

              • 4. Re: OSPF v3 vs OSPF v2
                Jon Major CCIE# 47884

                From the PDF you sent,


                Migration to IPv6

                Adding IPv6 means OSPFv2 and OSPFv3 in network

                Two protocols, two sets of identical configuration"


                That's only true if you decide against migrating to ospfv3 multiple address families. That said, it does mean downtime while migrating from ospfv2 to ospfv3.

                • 5. Re: OSPF v3 vs OSPF v2

                  Hi Jon,


                  Sure correct me if I am wrong --> ISIS advertises  ipv4 and ipv6 in a single topology, also it forms neighbor ship with the peer device through ISIS TLV (layer-2) ,So we can see only one neighbor ipv4 and ipv6.


                  OSPFV3 advertises ipv4 and ipv6 in a two different topology through OSPFv3 hellos,  It mains two separate neighbor ship with the remote device for ipv4 and ipv6, also its little bit constrain to the router to hold two different topologies.

                  • 6. Re: OSPF v3 vs OSPF v2
                    Liz Cacic

                    Hi everybody,


                    All the information discussed here are correct, but we are missing a few important details.

                    Let's me summary everything to ensure it's clear.



                         - It runs over Layer 2 protocol.

                         - It does not use IPv4 nor IPv6 header for the ISIS packets. IPv4 and IPv6 are only data, carried on TLVs.

                         - ISIS can run into two different ways in regards to building the tree (topology). The default varies per Cisco IOS software.

                              - Single topology: This means only one SPF tree is used to calculate the short path for both: IPv4 and IPv6. In this case, for every single link that has IPv4 you must have also IPv6 configured, otherwise you will have black hold for the IPv6 reachability.

                                   - Single topology is the default topology for Cisco IOS software.

                              - Multi topology: This means one SPF tree per address-family. One for IPv4 and another for IPv6. In this case, it's not required IPv6 in every single link that has IPv4 configured and vice-versa.

                                   - Multi topology is the default for Cisco IOS XR software.



                         - It runs over IPv4 protocol.

                         - It does advertise only IPv4 prefixes.



                         - It uses IPv6 link-local address. This means, as long as IPv6 is enable, even an global IPv6 address is not configured on the interface, it works.

                         - Global IPv6 address and IPv4 address are only in the payload of the OSPFv3 packets.

                         - LSA type 1 and LSA type 2, does not contain Global IPv6 addresses, instead it uses link-local addresses. OSPFv2 does use global IPv4.

                         - the SPF trees are build based on LSA type 1 and LSA type 2.

                         - Prefixes are carried in other LSAs, LSA type 3, type 4, type 5, type 7, type 8, and type 9.

                         - Type 8 and Type 9 are the new in OSPFv3.

                         - It builds one tree per address family. Similar to IS-IS multi-topology.



                    OSPFv3 is closer to IS-IS protocol in the sense, the tree is built not based on global prefixes.



                    In regards to the link you mentioned about. Everything mentioned about OSPF, it's about OSPFv2. Many characteristics of OSPFv2 does not apply on OSPFv3.

                    This following link has some highlights between OSPFv2 and OSPFv3.





                    Hope this clarify your confusion.


                    Kind Regards,


                    • 7. Re: OSPF v3 vs OSPF v2

                      yeah now its cleared Thanks Liz