OSPFv3 Fundamentals

ENCOR Course

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Table of Contents

an overview of the OSPFv3 routing protocol and the similarities to OSPFv2.

OSPFv3 supports IPv4 and IPv6 address families.
New LSA types have been created to carry IPv6 prefixes.
The IP prefix information is carried as LSA payload information, making the protocol essentially address family independent.
Includes a new link-state type field that is used to determine the flooding scope of LSA, as well as the handling of unknown LSA types.
OSPFv3 runs directly over IPv6, and the number of fields in the packet header has been reduced.

Router ID – The router ID is used to identify neighbors, regardless of the network type in OSPFv3. The router ID must always be manually assigned in the routing process.
Authentication – Neighbor authentication has been removed from the OSPF protocol and is now performed through IPsec extension headers in the IPv6 packet.
Neighbor adjacencies – OSPFv3 inter-router communication is handled by IPv6 link-local addressing.
Multiple subnets on an interface – Allows for neighbor adjacency to form even if the two routers do not share a common subnet.
Multiple instances – OSPFv3 packets include an instance ID field that may be used to manipulate which routers on a network segment are allowed to form adjacencies.

OSPFv3 packets use protocol ID 89.
Routers communicate with each other using the link-local address.
OSPFv3 modifies the structure of the router LSA (type 1).
It renames the network summary LSA to the interarea prefix LSA.
It renames the ASBR summary LSA to the interarea router LSA.
Router LSA is responsible for announcing interface parameters such as the interface type and metric.
IP address information is advertised independently by two new LSA types:
- Intra-area prefix LSA
- Link-local LSA
Link-state database(LSDB) creates a shortest path topology tree based on links instead of networks. Since IP address information is advertised using new LSA types there is no longer a need to run SPF calculations every time a new address prefix is added or changed on an interface.

LS Type	Name	Description
0x2001	Router	Every router generates router LSAs that describe the state and cost of the router’s interfaces to thearea.
0x2002	Network	A designated router generates network LSAs to announce all of the routers attached to the link,including itself.
0x2003	Interarea Prefix	Area border routers generate interarea prefix LSAs to describe routes to IPv6 address prefixes thatbelong to other areas.
0x2004	Interarea router	Area border routers generate interarea router LSAs to announce the addresses of autonomoussystem boundary routers in other areas.
0x4005	AS external	Autonomous system boundary routers advertise AS external LSAs to announce default routes orroutes learned through redistribution from other protocols.
0x2007	NSSA	Autonomous system boundary routers that are located in a not-so-stubby area advertise NSSA LSAsfor routes redistributed into the area.
0x0008	Link	The link LSA maps all of the global unicast address prefixes associated with an interface to the link-local interface IP address of the router. The link LSA is shared only between neighbors on the samelink.
0x2009	Intra-area prefix	The intra-area prefix LSA is used to advertise one or more IPv6 prefixes that are associated with arouter, stub, or transit network segment.

Destination address is either a unicast link-local address or a multicast link-local scoped address: FF02::05: OSPFv3 AllSPFRouters

Every router uses AllSPFRouters multicast address to send OSPF hello messages to routers on the same link.
Hello messages are used for neighbor discovery and detecting whether a neighbor relationship is down. DR and BDR routers also use this address to send link-state update and flooding acknowledgment messages to all routers.

FF02::06: OSPFv3 AllDRouters designated router (DR)

Non-DR/BDR routers send an update or link-state acknowledgment message to the DR and BDR by using the AllDRouters.
OSPFv3 uses the same five packet types and logic as OSPFv2.

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