Please enable JavaScript.
Coggle requires JavaScript to display documents.
Single-Area OSPFv2 Concepts, image, image - Coggle Diagram
Single-Area OSPFv2 Concepts
1.3 OSPF Operation
1.3.2 OSPF Operational States
Down:
No Hello received, router sends Hello.
Init:
Hello messages with Router ID are received.
Two-Way:
Two-way communication, DR/BDR election in multi-access.
ExStart:
It defines who starts and the DBD sequence number.
Exchange:
DBD exchange, if missing info, Loading, if not, Full.
Loading:
LSR/LSUfor extra routes, SPF calculation, then Full.
Full:
Synchronized database.
1.3.2 OSPF Operational States
Is a link-state
routing protocol
that establishes communication between routers through different operational states. These states are
sequential steps
that move from having no relationship with a neighbor to having a fully synchronized routing database.
1.3.3 Establish Neighbor Adjacencies
When
OSPF
is enabled on an interface, the router begins by sending Hello packets with its router ID to the multicast address 224.0.0.5. This marks the transition from the
Down State
to the Init State .
If another OSPF router, like R2, receives the Hello and recognizes a new router ID
, it will attempt to establish an adjacency, starting the OSPF neighbor relationship process.
1.3.4 Synchronizing OSPF Databases
ExStart State:
Routers decide which one sends first. The router with the highest Router ID starts the exchange.
Exchange State:
Routers send Database Description (DBD) packets summarizing their LSDBs.
Loading State:
If information is missing, routers send Link State Requests (LSRs) to get details.
1.3.5 The Need for a DR
Need for a DR in OSPF
Multiaccess issues:
Too many adjacencies.
Excessive LSA flooding.
Adjacency formula:
n(n - 1) / 2
Example: 5 routers = 10 adjacencies; 20 routers = 190.
1.3.6 LSA Flooding With a DR
Flooding LSAs
Problem:
One LSA triggers all routers to flood more LSAs.
Each LSA requires acknowledgments.
Effect:
In multiaccess networks, this creates chaotic traffic.
Conclusion:
Without control, LSA flooding overwhelms the network.
LSAs and DR
Solution: Elect a DR on multiaccess networks.
Roles:
DR → collects & distributes LSAs.
BDR → backup if DR fails.
DROTHERs → neither DR nor BDR.
Note: DR only manages LSAs; normal packet forwarding uses routing table.
1.1 OSPF Features and Characteristics
1.1.2 Components of OSPF
Data structures
Adjacency database - This creates the neighbor table.
Link-state database (LSDB) - This creates the topology table.
Forwarding database - This creates the routing table
Algorithm
SPF tree by placing each router at the root of the tree and calculating the shortest path to each node
Routing Protocol Messages
Packets are used to discover neighboring routers and also to exchange routing
1.1.3 Link-State Operation
Establish Neighbor Adjacencies
Exchange Link-State Advertisements
Build the Link State Database
Execute the SPF Algorithm
Choose the Best Route
1.1.4 Single-Area and Multiarea OSPF
Single-Area OSPF - All routers are in one area
Multiarea OSPF - OSPF is implemented using multiple areas, in a hierarchical fashion
.
1.1.5 Multiarea OSPF
Large routing domain can be divided into smaller areas, to support hierarchical routing.
Smaller routing tables
Reduced link-state update overhead
Reduced frequency of SPF calculations
1.1.6 OSPFv3
OSPFv3 and OSPFv2 run as separate processes, each with its own tables and configurations, although their configuration and verification commands are very similar.
1.2 OSPF Packets
1.2.2 Types of OSPF Packets
Type 1: Hello Packet
Establishes and maintains adjacency with other routers.
Type 2: Database Description (DBD)
Provides a summary of the LSDB.
Used to verify LSDB consistency among routers.
Type 3: Link-State Request (LSR)
Requests detailed info about specific LSDB entries from the DBD.
Type 4: Link-State Update (LSU)
Responds to LSRs.
Announces new information (contains LSAs).
Type 5: Link-State Acknowledgment (LSAck)
Confirms receipt of LSU.
Data field is empty.
1.2.3 Link-State Updates
Exchange process:
LSU → sends details/updates
LSU function:
Forwards routing updates (link changes)
Contains LSAs (info inside the packet)
LSR → requests details
LSAck → confirms receipt
DBD → summary of LSDB
Versions:
OSPFv2 → 11 LSA types
OSPFv3 → renamed + 2 new LSAs
1.2.1 OSPF Packets
Hello
Link-State Request(LSR)
Database Description(DBD)
Link-State Update(LSU)
Link-State Acknowledgment(LSAck)
1.2.4 Hello Packet
Purpose:
Discover OSPF neighbors & establish adjacency
Elect DR (Designated Router) & BDR on multiaccess networks (Ethernet)
Advertise parameters required for neighbor agreement
Not needed on point-to-point links
Module Practice and Quiz
What did I learn in this module?
Network concept → communication & resource sharing
Types of networks → LAN, WAN, Internet, Intranet, Extranet
Communication models → Client/Server, Peer-to-Peer
Evolution → convergence of voice, video & data
Modern network characteristics → Security, Reliability, Scalability, QoS
Protocols & standards → interoperability importance
Network sizes → Home, SOHO, Medium, Large, Global
