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CCNA - Topics

CCNA - ROUTING

RIP

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OSPF

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ROUTING

OSPF

OSPF Stand for Open Shortest Path First

Type                 : Link state Routing Protocol
AD Value            :110
Hello Timer         :10 sec
Update Timer      :None
Dead Timer         :4 Hellos
Transport           :89 (IP)
Multicast Add      :224.0.0.5-6

 

Open Shortest Path First (OSPF) is a dynamic routing protocol for use in Internet Protocol (IP) networks. OSPF is designated by the Internet Engineering Task Force (IETF). Specifically, it is a link-state routing protocol and falls into the group of interior gateway protocols, operating within an autonomous system (AS). Unlimited router can be used. CPU usage will be high, to reduce the CPU Usage using area.

An OSPF network can be divided into sub-domains called areas. An area is a logical collection of OSPF networks, routers, and links that have the same area identification. Kindly find the area details as below.

  • The backbone area, which is also referred to as Area 0. All other areas must connect to the backbone area. Hence, this area is obligatory.
  • An ordinary or standard area, which is an area that connects to the backbone (Area 0) and is treated as a separate entity. All routers in a standard area have the same topological database, but their routing tables will be based on the routers position in the standard area and will thus be unique to the router.
  • A stub area, which is an area that does not accept external summary routes. A router within a stub area can only see outside the autonomous system if a default route has been configuration for it.
  • A totally stubby area, which is similar to a stub area. In this area, the default route must be configured as 0.0.0.0. This type of area is useful for remote sites that have few networks and limited connectivity with the rest of the network and is a Cisco proprietary solution.
  • A not so stubby area (NSSA), which is a stub area that can receive external routes but will not propagate those external routes into the backbone area.

OSPF Network Type:

If you are working on OSPF then you need to know the different network types

  • Non broadcast - This is the default on frame relay networks.
    1. Default on Multipoint interface like Frame-relay
    2. Hello interval 30 seconds
    3. Dead Interval 120 seconds
    4. DR/BDR election
    5. Updates are sent as unicast
    6. Neighbor command required on hub router
    7. Next hop is not changed and remains the IP address of the originating router
  • Broadcast - This is the default on Ethernet/broadcast networks.  Does have DR/BDR election.
    1. Default on Ethernet
    2. Hello interval 10 seconds
    3. Dead Interval 40 seconds
    4. DR/BDR election
    5. Updates are sent as multicast
    6. Next hop  is not changed and remains the IP address of the originating router
  • Point-to-point – No DR/BDR election.  This one is pretty self explanatory.
    1. Default on HDLC, PPP and Frame-relay Point-to-Point
    2. Hello Interval 10 seconds
    3. Dead Interval 40 seconds
    4. No DR/BDR Election
    5. Multicast updates to 224.0.0.5
    6. Next hop address is that of the advertising router
  • Point-to-multipoint
    1. Cisco proprietary
    2. Host routes are added in the routing table
    3. Hello Interval 30 seconds
    4. Dead Interval 40 seconds
    5. No DR/BDR Election
    6. Multicast updates to 224.0.0.5
    7. Next hop address is that of the advertising router
    8. Frame-relay partial mesh
  • Point-to-multipoint non broadcast
    1. Cisco proprietary
    2. Hello Interval 30 seconds
    3. Dead Interval 120 seconds
    4. Frame-relay Partial Mesh
    5. No DR/BDR Election
    6. Unicast updates

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