OSPFv3 Routing Protocol Overview LSA And Packet Types

Januari 1, 2023Desember 23, 2022 falma.u99 ospfv3, overview, packet, protocol, routing, types

OSPF version 3 (OSPFv3) is the latest version of the OSPF routing protocol. OSPFv3 is designed as network protocol independent. OSPFv2 and OSPFv3 have numerous similarities, but since OSPFv2 runs on IPv4 and OSPFv3 runs directly over IPv6, there are significant changes to be noted.

OSPFv2 vs OSPFv3
Some of the notable differences between the OSPF protocols, OSPFv3 and OSPFv2, are the following:

1. OSPFv3 supports IPv4 and IPv6 addresses.
2. The Shortest Path Tree (SPT) calculations are per link.
3. Multiple instances of OSPFv3 can run on a single link.
4. The IP prefix information is conveyed as LSA payload information.
5. Prefixes are shown as prefix + prefix length.
6. There are two new LSA types.
7. There is a flooding scope for every LSA.
8. Interface commands are used to enable OSPFv3 on the interface.
9. The router ID is used to identify neighbors irrespective of the network type.
10. Router ID must be manually assigned.
11. OSPFv3 will advertise all of the multiple IPv6 prefixes on an interface.
12. Neighbors are manually specified using their IPv6 link-local addresses.
13. Neighbor adjacency can be formed even if they’re not in the same subnet.
14. An instance ID field is used to indicate which routers can form adjacencies.
15. IPsec authentication is used utilizing the IPv6 extension headers.

OSPFv3 LSA Types
The IPv6 OSPF version 3 LSA types are almost similar to OSPFv2. Two LSA types are renamed, Network Summary to Inter-Area Prefix LSA and ASBR Summary to Inter-Area Router LSA. The last two types are newly added to OSPFv3, the Link and Intra-Area Prefix LSAs. Type 6 Group Membership LSA is deprecated in OSPFv3.

OSPFv3 LSA TypeOSPFv3 LSA NameOSPFv2 LSA TypeOSPFv2 LSA NameLSA Description0x2001Router1RouterDescribes the state and cost of the router’s interfaces to the area.0x2002Network2NetworkAnnounces all the routers attached to the link, including itself.0x2003Inter-Area Prefix3Network SummaryArea border router uses this to describe routes to IPv6 address prefixes that belong to other areas. Also used to advertise a default route into a stub area.0x2004Inter-Area Router4ASBR SummaryArea border routers use this to announce the addresses of ASBRs in other areas.0x4005AS-External5AS-ExternalAnnounces routes learned through redistribution from other protocols and default routes.0x2006Group Membership6Group MembershipDeprecated from OSPFv3.0x2007NSSA7NSSA ExternalUsed for routes redistributed into the area.0x0008LinkMaps all of the global unicast address prefixes related to an interface to the router’s link-local interface IP address.0x2009Intra-Area PrefixUsed to advertise one or multiple IPv6 prefixes related to a router, stub, or transit network segment.The OSPFv3 LSA Types are in hexadecimal values. The first three values specify the flooding scope of the LSA. We have three flooding scopes:

* 0x0: Link-local scope – used for the Link LSA, only flooded on the local link.
* 0x2: Area scope – used for LSAs flooded through a single area.
* 0x4: AS scope – used for LSAs flooded throughout the OSPFv3 routing domain.

OSPFv3 Link-State Advertisement
Type 1 Router LSA in OSPFv3 is only now used for announcing interface parameters like interface type (point-to-point, virtual links, etc.) and metric. In OSPFv2, IP address prefixes are advertised in Type 1 Router LSA and Type 2 Network LSA. The said LSAs are utilized by the OSPF protocol Dijkstra algorithm to distinguish the Shortest Path Tree (SPT).

The new OSPFv3 LSA Types 8 and 9 advertise the IPv6 address information. The Link LSA is where the link-local addresses used for the next hops are advertised into. Link LSAs are flooded on the local link only, and they are shared between neighbors on the same link.

The Intra-Area Prefix LSA is where the IPv6 prefixes are advertised. These LSAs are flooded within the area only. The OSPFv3 Link-State Database (LSDB) builds a shortest path topology tree based on per link calculations and not per network.

Since the Shortest Path First (SPF) tree and the prefixes are separated in OSPFv3, when an interface’s link-local address changes, the router will flood an updated Link and Intra-Area Prefix LSAs only. The router doesn’t have to flood the Router and Network LSAs because there’s no change in the topology. There is no need to recalculate the SPT, unlike in OSPFv2, where the SPT is recalculated every time a new address prefix is added or changed on an interface.

OSPFv3 Packet Types
With the OSPFv3 routing protocol, the routers communicate using their IPv6 link-local address on their local interface as the source. The destination address can either be unicast link-local address or multicast link-local scoped address:

* FF02::5 – OSPFv3 AllSPFRouters
* FF02::6 – OSPFv3 AllDRouters Designated Router (DR)

The FF02::5, AllSPFRouters multicast address, sends OSPF hello messages to the routers on the same link. The hello messages are used for neighbor discovery and identifying neighbor relationship status. The AllSPFRouters address is also used by the DR and BDR routers to send link-state updates and flooding acknowledgment messages to all routers.

The FF02::6, AllDRouters address, sends an update or link-state acknowledgment message by non-DR/BDR routers to the DR and BDR.

The OSPFv3 packet types are the same as the OSPFv2 packet types. These are the following:

Packet TypePacket Type NameSourceDestinationPurpose1HelloLink-local AddressFF02::5Discovers and maintain neighborsLink-local AddressLink-local AddressInitial adjacency forming, immediate hello2Database DescriptionLink-local AddressLink-local AddressSummarize the database contents3Link-State RequestLink-local AddressLink-local AddressDatabase information request4Link-State UpdateLink-local AddressLink-local AddressInitial adjacency forming, link-state update responseLink-local address (from DR)FF02::5Database updateLink-local address (from non-DR)FF02::6Database update5Link-State AcknowledgmentLink-local addressLink-local addressInitial adjacency forming, link-state update responseLink-local address (from DR)FF02::5Flooding acknowledgmentLink-local address (from non-DR)FF02::6Flooding acknowledgment

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