Comparison Between OSPFv3 and OSPFv2

OSPFv3 and OSPFv2 are the same in the following aspects:

• Network type and interface type
• Interface state machine and neighbor state machine
• LSDB
• Flooding mechanism
• Five types of packets, including Hello, DD, LSR, LSU, and LSAck packets
• Route calculation

OSPFv3 and OSPFv2 are different in the following aspects:

• OSPFv3 is based on links rather than network segments.

  OSPFv3 runs on IPv6, which is based on links rather than network segments.

  Therefore, you need not to configure OSPFv3 on the interfaces in the same network segment. It is only required that the interfaces enabled with OSPFv3 are on the same link. In addition, the interfaces can set up OSPFv3 sessions without IPv6 global addresses.

• OSPFv3 does not depend on IP addresses.

  This is to separate topology calculation from IP addresses. That is, OSPFv3 can calculate the OSPFv3 topology without knowing the IPv6 global address, which only applies to virtual link interfaces for packet forwarding.

• OSPFv3 packets and LSA format change.

  • OSPFv3 packets do not contain IP addresses.
  • OSPFv3 router LSAs and network LSAs do not contain IP addresses, which are advertised by link LSAs and intra-area prefix LSAs.
  • In OSPFv3, Router IDs, area IDs, and LSA link state IDs no longer indicate IP addresses, but the IPv4 address format is still reserved.
  • Neighbors are identified by Router IDs instead of IP addresses in broadcast, NBMA, or P2MP networks.

• Information about the flooding scope is added in LSAs of OSPFv3.

  Information about the flooding scope is added in the LSA Type field of LSAs of OSPFv3. Thus, OSPFv3 routers can process LSAs of unidentified types, which makes the processing more flexible.

  • OSPFv3 can store or flood unidentified packets, whereas OSPFv2 just discards unidentified packets.
  • OSPFv3 floods packets in an OSPF area or on a link. It sets the U flag bit of packets (the flooding area is based on the link local) so that unidentified packets are stored or forwarded to the stub area.

  For example, FW_A and FW_B can identify LSAs of a certain type. They are connected through FW_C, which, however, cannot identify this type of LSAs. When FW_A floods an LSA of this type, FW_C can still flood the received LSA to FW_B although it does not identify this LSA. FW_B then processes the LSA.

  If OSPFv2 is run, FW_C discards the unidentified LSA so that the LSA cannot reach FW_B.

• OSPFv3 uses IPv6 link-local addresses.

  IPv6 implements neighbor discovery and automatic configuration based on link-local addresses. Routers running IPv6 do not forward IPv6 packets whose destination address is a link-local address. Those packets can only be exchanged on the same link. The unicast link-local address starts from FE80/10.

  As a routing protocol running on IPv6, OSPFv3 also uses link-local addresses to maintain neighbor relationships and update LSDBs. Except Vlink interfaces, all OSPFv3 interfaces use link-local addresses as the source address and that of the next hop to transmit OSPFv3 packets.

  The advantages are as follows:

  • The OSPFv3 can calculate the topology without knowing the global IPv6 addresses so that topology calculation is not based on IP addresses.
  • The packets flooded on a link are not transmitted to other links, which prevents unnecessary flooding and saves bandwidth.

• OSPFv3 packets do not contain authentication fields.

  OSPFv3 directly adopts IPv6 authentication and security measures. Thus, OSPFv3 does not need to perform authentication. It only focuses on the processing of packets.

• OSPFv3 supports two new LSAs.

  • Link LSA: A router floods a link LSA on the link where it resides to advertise its link-local address and the configured global IPv6 address.
  • Intra-area prefix LSA: A router advertises an intra-area prefix LSA in the local OSPF area to inform the other routers in the area or the network, which can be a broadcast network or an NBMA network, of its IPv6 global address.

• OSPFv3 identifies neighbors based on router IDs only.

  On broadcast, NBMA, and P2MP networks, OSPFv2 identifies neighbors based on IPv4 addresses of interfaces.

  OSPFv3 identifies neighbors based on router IDs only. Thus, even if global IPv6 addresses are not configured or they are configured in different network segments, OSPFv3 can still establish and maintain neighbor relationships so that topology calculation is not based on IP addresses.