Saturday, 10 September 2016

OSPF - Part 2

OSPF Terminology 

1.)  Link State Database (LSDB)
       Every OSPF  router store this topology information in its topology database, sometime its called
       LSDB. LSDB have best, lowest cost for each prefix/length.

2.) Shortest path first (SPF)
      It is name of alogrithm. OSPF uses to analyze the LSDB.

3.) Link State Update (LSU)
      It is a packet which hold the detailed topology information. Specially LSA.

4.) Link State advertisement
      It is class of OSPF database structure which hold the topology information. LSA are held in an
      LSDB and communicate over a network in LSU messages.

5.)  Area
      A contiguous grouping of routers and interfaces. Router learn all topology information about the
      area, it do not learn about different areas.

6.) Area Border Router (ABR)
      A router that has interfaces connected to at least two different areas, including with 
      backbone  area. ABR hold topology data for each area, calculate routes for each area and    
      advertise those routes between areas.

7.)  Backbone router 
       Any router that has at least one interface connected to the bacbone area.

8.) Designated router
9.) Backup Designated Router 

OSPF Configuration Command: 

 Router(config)# router ospf  <process id>
 Router(config-router)# network <network-id> <wildcard mask> area <area-id>

CISCO IOS only enables ospf an interface neighbors on that interface matched by an ospf network command. When enabled, the router does the following:

  1.) Attempt to discover ospf neighbors on that interface  by sending multicast ospf hello message.
  2.) Include  the connected subnet in future topology database exchange.

OSPF Verification Command:

   1.) Show ip protocols
          List the contents of the network configuration commands for each routing process.

   2.)  Show ip ospf neighbors
          List of known neighbors, including neighbor state.

   3.) Show ip ospf database 
          List of all LSAs for all connected area
   4.) Show ip route
          List the content of the IP routing table. 

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