OSFP

                                                                      OSPF ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++.

• .Standard protocol.
• .It link State protocol.
• .Unlimited hop count.
• .Using Metric to calculate the B.W (cost=10^8/B.W)
• .Administrative distance is 110.
• .It is a classless routing protocol.
• .It supports VLSM and CIDR.
• .It support only equal-cost load Balancing.

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• Updates are sent to multicast address 224.0.0.5
• Faster convergence.
• Send Hello packet every 10 second & Dead = 40 sec
• incremental updates 

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 7 stages process 

• 1 Downstate
• 2 Attempt/Init state    (exchange hello mess) 
• 3 Two ways state       (neighbors relationship ) 
• 4 Exstart state           (not exstart decide to exchange )
• 5 Exchange state
• 6 Loading state
• 7 Full state

Downstages both router don't have any route to each other when we advertise the interface using the command Router OSPF (number) and network ...................either we can using wildcard mask or the IP on the psychical interface there is servo way to configure it, it the all depends on how we want to configure it. Now when the router A try to advertise  the interface
using the command it will send hello mess with a multicast address 244.0.0.5 and the router-id same thing with route b when router b try to advertise their interface using the command
router b will send back with Hello mess with the unicast address and the own Router ID, by the way, this is initially State. After that will exchange their router-id and be become neighbors relationship

Using Show IP OSPF neighbors  

Neighbor ID    Pri    State        Dead Time          Address           Interface
1.1.1.1        1     FULL/DR       00:00:31          172.16.5.1      FastEthernet0/0

Router# show IP protocols 
Routing Protocol is "OSPF 1"
Outgoing update filter list for all interfaces is not set 
Incoming update filter list for all interfaces is not set 
 Router ID 2.2.2.2
 Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Maximum path: 4
Routing for Networks:
 172.16.5.2 0.0.0.0 area 0
 2.2.2.2 0.0.0.0 area 0
Routing Information Sources:  
Gateway         Distance      Last Update 1.1.1.1              110      00:08:21
2.2.2.2              110      00:07:54
 Distance: (default is 110)

Router#show IP OSPF database 
 OSPF Router with ID (2.2.2.2) (Process ID 1)
  Router Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         615         0x80000003 0x006d43 2
2.2.2.2         2.2.2.2         588         0x80000003 0x007b28 2
                Net Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum
172.16.5.1      1.1.1.1         615         0x80000001 0x00a2a9

Router ID

Now, what is Router ID think as a name of the router: router id not a random choice. the router choice the router IP base on the height IP address on an active physical interface, we can give a router a loop IP address and turn it into router id by using command router-iD(address), loop interface is a logical interface will never come down.

In Exstart Sate they not exchange the DBD information they decide to Exchange the route with higher router id address will start to exchange is first.
DBD is a summary of The LSDB is a database of all OSPF router

 OSPF must have the same database 

In the loading states,  the router A will check to compare to make sure that they have the same database from a neighbor if there an extra network they will send LSR request LSR stand for (Link Sate Request ) and after they will receive that Database
LSACk and complete full State 

Problem: OSPF full neighborship is not coming up between routersCause :
1. Hello, and Dead timer or Area ID, Authentication password/type/key or Area type are mismatches between router.
2. Trying to build OSPF neighborship on the secondary address.
4.  OSPF not enabled on the correct interface or network command is wrong.
5. Network type is NBMA and no neighbor map configured with a broadcast option.
6. High CPU  or OSPF packet is dropped by interface due to queuing or high rate or hardware issue from an interface to CPU path.
7. Mismatch Subnet mask is configured. 
8. "passive interface <> " is configured under "router OSPF" for the interface.
9.  Mismatch Network type is configured.
10. The router is configured with  IP OSPF priority 0 on the router.
11. Neighborship is getting built over the virtual link on a stub area.

OSPF Troubleshooting commands

Show IP OSPF neighbor

show Ip OSPF neighbor detail

show Ip OSPF

show Ip OSPF database

show Ip OSPF interface

show Ip OSPF database database-summary 

show Ip OSPF virtual link

show Ip OSPF database self-originate.

show Ip OSPF database adv-router

show Ip OSPF statistics
show Ip OSPF request-list
show Ip OSPF bad
debug Ip OSPF adj
debug IP OSPF monitor