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Can we run OSPFv2 on few interfaces and OSPFv3 on few interfaces within the same system? Can we run both OSPF v2 and v3 as different processes?

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Sure, this is possible, depending on the router model and software. OSPFv2 is for IPv4 only and OSPFv3 for both IPv4 and IPv6. There are however differences in the implementation of both protocols (as these are two completely independent protocols), depending on the vendor and sometimes even on the model.

Consider Cisco for example: In regular IOS and IOS-XE, you can run both protocols at the same time, even for IPv4. Note however, when running both OSPFv2 and OSPFv3 for IPv4, routes learned via OSPFv2 will always take precedence, ignoring "normal" OSPF route selection rules, which are only evaluated within a process.

On IOS-XR, for example, OSPFv3 is not even supported for AF IPv4, only for IPv6.

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  • You've missed that OSPF v1/v2 can only carry the IPv4 address family and that OSPFv3 can only carry the IPv6 address family. The design intent is that both OSPFv2 and OSPFv3 run simultaneously and independently in a dual-stack network (which is good thing in practice, as it limits blackholing). – vk5tu Dec 23 '16 at 22:49
  • No, this is not correct. As written in my answer, OSPFv1/v2 can only carry IPv4, but OSPFv3 can carry both AF IPv4 and IPv6, even in the same process. Actually, in OSPFv3 the topology is built only once (using the LSA types 1 and 2), but the prefix LSAs can contain prefixes from multiple AFs. Compare RFC 5838. – waza-ari Dec 23 '16 at 23:10
  • If OSPFV3 carries both AF IPV4 and IPV6 and updates routes, then what happens when we OSPFV2 and V3 ? whether V2 IPV4 routes will get precedence over V3 IPV4 routes ? – user2857290 Dec 27 '16 at 9:35
  • @user2857290: Unfortunately I cannot proof my theory, because I could not find it documented anywhere. From what I've seen, Cisco IOS and IOS-XE in recent versions always prefer OSPFv2 over OSPFv3 in case of equal IPv4 routes. Probably, just guessing, because OSPFv2 is the "native" IPv4 protocol. – waza-ari Dec 27 '16 at 13:31
  • No worries. If one of the answers above answers your question, please accept it by clicking the check mark symbol next to it. Otherwise the question will remain open and pop up again on a regular basis. – waza-ari Dec 29 '16 at 9:39
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Yes, OSPFv2 and v3 are completely different and independent protocols.

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As long as they are defiened on that router, so sure we can run OspfV2 on few interfaces and OspfV3 on few interfaces within the same system.

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