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Key features	Link State-protocol: #each router adv about the state of his links / interface's subnet Hierarchical , Area type: backbone, std , Stub, NSSA All routers share the same database when in the same Area Route redistribution ( from/to other protocol ) + summarization OSPF-TE: carry BW,
Dijkstra / SPF Algorithm	1- place the source router at the root of the tree 2- calculate the cost ( Ref BW/link BW) to the destination 3- pick the one with the lowest cost 4- if same cost lowest RID ( def= system Mac@) OSPF-TE: build a separate tree with all other constrate: BW, ...
OSPF Frame	\| LL \| IP header ( protocol id= 89 ) \| OSPF packet type \| LT \| 14B 20B 20B + Data

OSPF Message

Link Layer / Link Trailer OSPF Header: Ver , Packet Type/Length , RID/AreaID, Checksum, Auth type/key
Multicast @ ( + unicast)	L3 Multicast address: All OSPF

Node

speaker: 224.0.0.5 All DR/BDR: 224.0.0.6 L2 Multicast address: 01-00-5E-00-00-05 & 01-00-5E-00-00-06 Unicast in case of repeat: LSR could be drop,
OSPF Packet Type	1- Hello 2- Database Descriptor 3- Link State Request 4- Link State Update 5- Acknowledge ( All LS messages are acknowledge )
OSPF Packet Type 1: Hello
OSPF Packet Type 2: Database Descriptor
OSPF Packet Type 3: Link State Request
OSPF Packet Type 4: Link State Update
OSPF Packet Type 5: Acknowledge

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