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OSPF Network Types Example

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OSPF Network Types:

[boxads] There are several kind of OSPF Network Types are use in service provider environment. OSPF message addresses are determined by the type of network to which the OSPF interface is connected. One of the following OSPF network types must be selected when configuring an interface on an OSPF router.

Point-to-Point:  A network that can connect only two routers. Leased-line WAN links such as Dataphone Digital Service (DDS) and T-Carrier are point-to-point networks. OSPF messages sent on point-to-point networks use IP multicast addresses.

  • No DR/BDR concept.
  • Has a Master and Slave concept instead, with highest interface chosing the Master, but can be manually set.
  • Default Priority = 0
  • Multicast = 224.0.0.5
  • Hello Timer = 10
  • Hello Dead Timer = 40
  • 1 Common Subnet
Point to point OSPF network
Point to point OSPF network

Point-to-Multipoint: A point-to-multipoint configuration approaches the non-broadcast limitation in a different manner. Rather than trying to emulate broadcast capability, it seeks to organize the PVCs into a collection of point-to-point networks. Hello packets must still be replicated and transmitted individually to each neighbor, but the multipoint approach offers two distinct advantages: no DR/BDR is needed, and the emulated point-to-point links can occupy a common subnet.

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OSPF LSA Types with Example

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OSPF LSA Types:

[boxads] There are different types of link-state advertisements (LSAs) that would be used for Open Shortest Path First (OSPF). This article contains List of OSPF LSA types with a short description. LSAs build up the OSPF link state database (LSDB), and they are exchanged between OSPF enabled nodes. Bellow short description of OSPF LSA types.

  • LSA Type 1 (Router LSA): LAS type 1 are generated by every router of an OSPF area. They are flooded to all other routers only inside an area of origin & directly connected router. In the link-state ID you will find the originating router’s ID.
  • LSA Type 2 (Network LSA): LSA type 2 are generated by DR  and flooded into the area of origin. The link-state ID will be the router ID of the DR.

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OSPF Message Types / Packet Types

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OSPF Message Types:

[boxads] There are several types of message are passes through OSPF network for communication each other. that OSPF Message Types are given bellow:

1. Hello : These messages are used to establish neighbor ship and serve as keepalives among other things. They are also used to elect the Designated Router (DR) and Backup Designated Router (BDR) on multiaccess networks (like Ethernet or Frame Relay).

Sent on 224.0.0.5 and 224.0.0.6

Contains the following in the packet;

  • RID of interface
  • Authentication
  • Hello Dead Timers
  • Area ID
  • Nieghbor List (If not a nieghbor, sends more info)
  • Designated Router IP
  • Backup DR IP
  • Priority of Interfaces

Hello interval: indicates how often it sends Hello packets. By default, OSPF routers send Hello packets every 10 seconds on multiaccess and point-to-point segments and every 30 seconds on non-broadcast multiaccess (NBMA) segments (like Frame Relay, X.25, ATM).

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Dead interval: number of seconds this router should wait between receiving hello packets from a neighbor before declaring the adjacency to that neighbor down.

2. Database Descriptor (DBD or DD) : These messages send summaries of a router’s known LSAs to a new neighbor.  Receiving routers can use this information to compare to their database and ask for more details if needed.

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OSPF Area Types With Example

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OSPF Area Types:

[bodyads] OSPF is a widely used protocol in service provider environments. Now a days the majority of the network setups use this protocol. OSPF is well suited for multi-vendor environments. OSPF allows 5 different area types, which provides flexibility, fast convergence and scalability. OSPF area types are:

  1. Backbone/ Non-backbone
  2. Stub Area
  3. Totally Stubby Area
  4. Not-So-Stubby Area (NSSA)
  5. Totally Not-So-Stubby Area (NSSA)
ospf area types with LSA
ospf area types with LSA

Backbone area:

The backbone area is the core of an OSPF network (also this area known as area 0 or area 0.0.0.0). All other areas are connected to backbone area, and inter-area routing happens via routers connected to the backbone area and to their own associated areas. The backbone area is responsible for distributing routing information between non-backbone areas. The backbone must be contiguous, but it does not need to be physically contiguous; backbone connectivity can be established and maintained through the configuration of virtual links.

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