OSPF Non-Broadcast Network Type over Frame-Relay

Lessons Discussion
60

Hello Muhammad

OSFP network types are a special case of OSPF implementation. They are used in order to accommodate specific technologies such as frame relay. It is for this reason that they are only described after the main topic of OSPF.

In any case, the reason they exist is that technologies such as frame relay cannot support broadcast and multi access infrastructure, which are prerequisites for normal OSPF functionality. The various types of networks are used to allow OSPF to have DR and BDR elections as well as to form neighbor adjacencies even without broadcast and multicast functionality. Here is a brief summary of these network types and when they should be used:

The following list explains the characteristics of the OSPF network types:

Broadcast - Used on normal Ethernet networks

  • The Broadcast network type is the default for an OSPF enabled ethernet interface.
  • The Broadcast network type requires that a link support Layer 2 Broadcast capabilities.
  • The Broadcast network type has a 10 second hello and 40 second dead timer.
  • An OSPF Broadcast network type requires the use of a DR/BDR which are automatically elected.

Non-Broadcast - used for frame relay physical interfaces

  • The Non-Broadcast network type is the default for OSPF enabled frame relay physical interfaces.
  • Non-Broadcast networks requires the configuration of static neighbors because broadcast traffic cannot be sent
  • The Non-Broadcast network type has a 30 second hello and 120 second dead timer.
  • An OSPF Non-Broadcast network type requires the use of a DR, but the hub must always be DR for it to work so the spokes should have a priority of 0

Point-to-Point - used between two directly connected routers regardless of the technology used

  • A Point-to-Point OSPF network type does not maintain a DR/BDR relationship.
  • The Point-to-Point network type has a 10 second hello and 40 second dead timer.
  • Point-to-Point network types are intended to be used between 2 directly connected routers.

Point-to-Multipoint - used for frame relay with the broadcast keyword for frame relay maps

  • OSPF treats Point-to-Multipoint networks as a collective of point-to-point links, thus no DR/BDR elections take place.
  • Point-to-Multipoint networks do not maintain a DR/BDR relationship.
  • Point-to-Multipoint networks will have an automatic neighbor discovery, so no need to manually configure them.
  • The Point-to-Multipoint network type has a 30 second hello and 120 second dead timer.

Point-to-Multipoint Non-Broadcast - non broadcast layer 2 topologies

  • Same as Point-to-Multipoint but requires static neighbors. Used on Non-broadcast layer 2 topologies.
  • Gives you the ability to define link cost on a per neighbor basis.

A more detailed description of each type is given within the lesson for each one.

I hope this has been helpful!

Laz

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