OSPF3C.1 # OSPF STATE AND EXPLAIN
OSPF is link state routing protocol has complete knowledge of network topology, allowing routers to calculate routes based on incoming requests. OSPF protocol has no limitations in hop count. OSPF uses link-state information to make routing decisions, making route calculations using the shortest-path-first (SPF) algorithm (also referred to as the Dijkstra algorithm), used to distribute IP routing information throughout a single Autonomous System (AS) in an IP network
When OSPF adjacency is formed, a router goes through several state changes before it becomes fully adjacent with its neighbor. Establish neighbor adjacencies: OSPF-enabled routers must form adjacencies with their neighbor before they can share information with that neighbor. An OSPF-enabled router sends Hello packets out all OSPF-enabled interfaces to determine whether neighbors are present on those links
Its working/operation is so complicated and we can divide into three major categories.
- Neighbor relationship: OSPF router first established the relationship from a neighbor. Provide a foundation for all continuing OSPF communications.
- Database exchange: After the established routers exchange the contents of their LSDBs.
- Route calculation: When router share the topology base data then they use the SPF algorithm for calculate the best route to add the routing address in routing table.
# Difference Between Distance Vector and Link
Distance vector protocols send their entire routing table to directly connected neighbors. Link state protocols send information about directly connected links to all the routers in the network. Distance vector protocols have slow convergence and suffer from the count-to-infinity problem
# OSPF Tables and Messages OSPF routing protocol will generate three type of table and also each OSPF router stores routing and topology information in three tables Neighbor table is defined as stores information about OSPF neighbors. Topology table is defined as stores the topology structure of a network. and Routing table is defined as stores the best routes.
There are several messages which are used in OSPF in order to share data bits from one router to another router.
- Link State Request (LSR): Requests specific link-state records from an OSPF neighbor.
- Link State Update (LSU): Sends specific link-state records that were requested. This packet is like an envelope with multiple LSAs in it./li>
- Link State Acknowledgement (LS-Ack): OSPF is a reliable protocol, so we have a packet to acknowledge the others.
- OSPF Neighborship Requirements.
- Summary Support our work
It is the name of data structure and holds the information of topology. LSAs are held the memory in the LSDB. Communication is over the network in message.LSAs are identified by OSPF RID of advertising router, LSA sequence number, An age in seconds (How much old is this LSA)
There are several types of LSAs: Router LSA, Network LSA, Area summary LSA, ASBR summary LSA, External LSA type 1, External LSA type 2
3C.2 # UNDERSTAND THE OSPF STATES
- Down State: First OSPF neighbor state no information (hellos) has been received from this neighbor but hello packets can still be sent to the neighbor.
- Attempt State: This state is only valid for manually configured neighbors in an NBMA environment. Router sends unicast hello packets every poll interval to the neighbor from which hellos have not been received within the dead interval.
- Initial State: Router received a hello packet from its neighbor but the receiving router’s ID was not included in the hello packet.
- 2 Way State: State is attained when the router receiving the hello packet sees its own router ID within the received hello packet. Router has seen the other’s hello packet.
- Exstart State: Actual process of exchanging link state information can start between the routers. Master/slave relationship is established and the initial sequence numbers are exchanged.
- Exchange State: DBD packets are exchanged. Contain the LSA header information and this information will be used by routers to see what LSA’s they have and what LSA’s they don’t have.
- 7) Loading State: Actual exchange of OSPF database information happens LSR’s are generated to request for missing LSA’s requests are fulfilled by LSU’s packets.
- Full State: Routers have a synchronized database after the LSR/LSU exchange process. Exchange LSAck’s with each other to confirm and move on to full state.
Its are 32-bit numbers written in dotted decimals just like an IP address because they identify be unique for each router. Using an IP address is a convenient way to find a default RID. Alternatively, the OSPF RID can be directly configured.
# OSPF Router TypesIt defines the following router types:-
- Area border router (ABR): It always found on area of border in between the two routers.
- Autonomous system boundary router (ASBR): That’s router always stand on the border and provide the services of other AS router from first router.
- Internal router (IR): It always keeps interior particular area.
- Backbone router (BR): It is related to any type of backbone. And it is existing only single area.
Router are send and receive the information to each other for become a neighbor is known as Hello process include such as Router ID, Area ID, Hello interval, Dead interval, List of neighbors, Router priority, RID designated router, RID backup DR, etc.
# Wildcard Mask It is represented four octets and its 32 bits, indicates which part of an IP address can assume any value written same as Net mask of subnet mask. It has a minor difference from subnet mask because this is the alternative of subnet mask.
Uses:
1) Size of a network or subnet for some routing protocols as like OSPF.
2) What IP addresses should be permitted or denied in access control lists (ACLs).
How to find out the wild card address form subnet mask ?
255 255 255 248
Sol. 255 255 255 255 - 255 255 255 248 = 0 0 0 7
It is a logical collection of OSPF network, OSPF router and OSPF links have the same Area identification. Each OSPF router must keep the LSA of every other router in its LSDB. Each router in a large OSPF AS has a large LSDB.
- Must maintain a Topological database for the Area to which it belongs.
- Doesn’t have detailed information about network topology outside of its area.
- Reducing the size of its Database.
- Combines a set of independent areas into a single domain-must exit and it have a backbone area.
- And each non-backbone area must be directly connected to the backbone area.
3C.3 # OPEN SHORTEST PATH FIRST PROTOCOL CONFIGURATION
Diagram:-
| Port | Status | Device |
|---|---|---|
| Router | ||
| Serial 0/0 | Routed link-port | Side_A |
| Serial 0/0 | Routed link-port | Side_B |
| Serial 0/1 | Routed link-port | Side_B |
| Serial 0/0 | Routed link-port | Side_C |
| Switch_Layer 2 | ||
| FastEthernet 0/1 | Trunk port | Switch0 |
| FastEthernet 0/1 | Trunk port | Switch1 |
| FastEthernet 0/1 | Trunk port | Switch2 |
| Broadcast n Collision domain status | ||
| Number of broadcast domain | Number of collision domain | |
| 5 | 11 |
# OSPF Configuration Lab : -
1) Configuration of Side_A
Router >enable
Router #configure terminal
Router (config)#hostname Side_A
!
Side_A (config)#interface FastEthernet0/0
Side_A (config-if)#ip address 192.168.1.1 255.255.255.0
Side_A (config-if)#no shutdown
Side_A (config-if)#exit
!
Side_A (config)#interface Serial0/0
Side_A (config-if)#ip address 10.10.10.1 255.0.0.0
Side_A (config-if)#encapsulation hdlc
Side_A (config-if)#clock rate 64000
Side_A (config-if)#no shutdown
Side_A (config-if)#exit
!
Side_A (config)# router ospf 760
Side_A (config-router)# network 10.0.0.0 0.0.0.255 area 0
Side_A (config-router)# network 192.168.1.0 0.0.0.255 area 0
Side_A (config-router# exit
!
2) Configuration of Side_B
Router >enable
Router #configure terminal
Router (config)#hostname Side_B
!
Side_ B (config)#interface FastEthernet0/0
Side_ B (config-if)#ip address 192.168.2.1 255.255.255.0
Side_ B (config-if)#no shutdown
Side_ B (config-if)#exit
!
Side_ B (config)#interface Serial0/0
Side_ B (config-if)#ip address 10.10.1.2 255.0.0.0
Side_ B (config-if)#no shutdown
Side_ B (config-if)#exit
!
Side_ B (config)#interface Serial0/0
Side_ B (config-if)#ip address 20.20.2.1 255.0.0.0
Side_ B (config-if)#encapsulation hdlc
Side_ B (config-if)#clock rate 64000
Side_ B (config-if)#no shutdown
Side_ B (config-if)#exit
!
Side_ B (config)# router ospf 760
Side_ B (config-router)# network 10.0.0.0 0.0.0.255 area 0
Side_ B (config-router)# network 20.0.0.0 0.0.0.255 area 0
Side_ B (config-router)# network 192.168.2.0 0.0.0.255 area 0
Side_ B (config-router# exit
!
3) Configuration of Side_C
Router >enable
Router #configure terminal
Router (config)#hostname Side_C
!
Side_C (config)#interface FastEthernet0/0
Side_C (config-if)#ip address 192.168.3.1 255.255.255.0
Side_C (config-if)#no shutdown
Side_C (config-if)#exit
!
Side_C (config)#interface Serial0/0
Side_C (config-if)#ip address 20.20.2.2 255.0.0.0
Side_C (config-if)#encapsulation hdlc
Side_C (config-if)#clock rate 64000
Side_C (config-if)#no shutdown
Side_C (config-if)#exit
!
Side_C (config)# router ospf 760
Side_C (config-router)# network 20.0.0.0 0.0.0.255 area 0
Side_C (config-router)# network 192.168.3.0 0.0.0.255 area 0
Side_C (config-router# exit
!
# OSPF TROUBLESHOOTING
Router (config) #show ip ospf neighbors
Router (config) #show ip route
Router (config) #show ip protocols
Router (config) #show ip ospf neighbors detail
Router (config) #show ip eigrp traffic
Router (config) #show protocols Router (config) #debug ospf packets
Router (config) #debug ospf packets terse
# Debugging command for troubleshooting
• Router# debug ip ospf packet (Function: show hello packet being sent and received on your router)
• Router# debug ip ospf hello (Function: show hello packet being sent and received on your router)
• Router# debug ip ospf adj (Function: show DR and DBR elections on a broadcast and non-broadcast multi – access network)
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