OSPF - Part 3

OSPF Router-id

1.)  It is 32-bit number assigned to each router running the ospf protocol.

2.)  It is uniquely identify of the router within an autonomous number.

3.)  It elects based on highest loopback ip address of router, otherwise highest non-loopback 

       ip  address of router.

4.)  We can set manually ospf router id:

       In ospf router subcommand:   router-id <router-id>

OSPF  Feature 

1.)  Transport

        IP protocol type 89 (Does not use TCP and UDP)

        OSPF need to perform reliable multicasting because it need talk to multiple possible neighbor 

        on the same network segment. Now, TCP does not support multicasting and UDP is reliable

        not.  Therefore, OSPF implements its own transport mechanism that allows both for reliability 

         (acknowledgments and retransmission of lost segments) and multicasting, bypassing both TCP 

         and UDP. 

2.)  Metric

        Based on cost of all outgoing interfaces in a route.

3.)  Hello interval

       Interval which route sends OSPF hello messages out of an interface. By default OSPF send hello

       messages in every 10 second on ethernet link and 30 second on WAN link.

   

       Note : OSPF send fast hello messages less than 1 second.

       Follow this link:

      

http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/fasthelo.html#wp1027195

 4.) Dead - Timer

       Timer used to determine when neighbor router has failed. OSPF router send dead message every 

        40 second. 

 5.)  Update Destination address

        Normally send to 224.0.0.5 (all SPF router) and 224.0.0.6 (all DR) router.

 6.)  Full or Partial update

       Full update used when new neighbor are discovered. Partial update used otherwise.

7.)  Authentication

      Support MD-5 and Clear-text authentication.

  

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