OSPF LSA type
LSDB Link State Database
- DR Designated Router, responsible for flooding process on the multi-access network. Each router on the network forms an adjacency with Designated Router.
- Backup Designated Router(BDR), DR failure BDR can very quickly take responsibility and become DR.
LSA – Link-state Advertisement, Each router generates one LSA describing itself: its links and neighbors.
Area – OSPF divides the network into multiple smaller areas.Routers need to have the same topology database within same area, but don’t have to know the topology of entire OSPF network.
LSA 1 – Router LSA
-generated by all OSPF routers
-most fundamental LSA and it lists all interfaces of a router to other routers or other networks
-flooding of LSA Type 1 is limited only to originating area
LSA 2 – Network LSA
-generated by Designated Routers on every multi-access network (like Ethernet)
-lists all routers connected to the same segment
-flooding of LSA Type 2 is also limited only to originating area
LSA 3 – Network Summary LSA
-originated by Area Border Router (ABR)
-send only to a single area to advertise information to Internal Routers about destinations outside that area
LSA 4 – Autonomous System Border Router(ASBR) Summary LSA
-send only between ABRs and announce which ABR in the network works as the ASBR
-not limited
LSA 5 – External LSA
-inject IP prefixes originated by other routing protocols into OSPF domain
-originated by ASBRs
- flooded to all areas (except stub areas) and are received by all Internal Routers
IP prefix redistribution
process of inserting IP routing information into protocol from outside
OSPFv3
OSPFv2/IPv4
- Flooding,information distribution mechanism
- DR election
- Areas
- SFP calculation
OSPFv3 supports only IPv6,not backward compatible with OSPFv2
OSPFv3 diff from OSPFv2
1) OSPFv2 interface is connected to a subnet
OSPFv3 interface is connected to a link, link means VLAN, could be multi-subnet
2) Removal of addressing semantics from the OSPF protocol packets and the main LSA types, leaving a network protocol independent core
3) OSPFv2 is inconsistent in its neighbor identification;OSPFv3 neighbors are always identified by RID, on all link types
4) Flooding scopes
- Link-local scope. The LSA is flooded only on the local link, and no further. This is used for the new Link-LSA
- Area scope (AS). The LSA is flooded throughout a single OSPF area only. This is used for Router-LSAs, Network-LSAs, Inter-Area-Prefix-LSAs, Inter-Area-Router-LSAs and Intra-Area-Prefix-LSAs.
- AS scope. The LSA is flooded throughout the routing domain. This is used for ASexternal- LSAs.
5) Link-Local Unicast address, ND, configed by auto-config, not forwarded by routers,FE80::/10 Prefix
6) Authentication changes,Authentication Header and Encapsulating Security Payload to ensure integrity and authentication/confidentiality of routing exchanges
7) Unknown LSA types, OSPFv3 treats unknown LSAs more similarly to the way IS-IS treats unknown TLVs (Type-Length-Values), forwarding them rather than
discarding them
Similarities between OSPFv2 and OSPFv3
1) OSPFv3 uses the same five packet types as OSPFv2, namely : Hello,
Database Description, Link State Request, Link State Update and
Link State Acknowledgment packets.
OSPFv3 packets use the same multicast procedures as OSPFv2.
For IPv6, the All SPF Routers multicast address is FF02::5 and the All
DRouters multicast address is FF02::6.
3) OSPFv3 Packet header
The packet formats of OSPFv3 differ little from those of OSPFv2. Most of the differences are in the packet headers and in the Hello packets.
The most noticeable difference between the two headers is the elimination of the authentication fields in OSPFv3.