OSPF Routing Protocol
How does OSPF routing protocol work?
OSPF is a routing protocol that is widely used in enterprises and service providers. It uses the concept of areas, which are logical groupings of contiguous networks. These networks are grouped together to reduce the number of routing tables that need to be maintained by an organization.
OSPF uses a link state algorithm to determine the best path for data packets. This makes it more reliable than other protocols, such as RIP, because it doesn’t rely on periodic updates from neighbors or other routers.
What is the OSPF Link State Algorithm?
The OSPF Link-State Algorithm (LSA) is a routing protocol for IP networks. It is the most widely used interior gateway protocol, both in commercial and academic networks.
The OSPF LSA works by creating a map of the network topology, and then assigning a cost to each link between any two nodes in the network. The lowest cost path from one node to another is then chosen as the best path to use.
These are the 7 OSPF LSA types:
Type 1: Router LSA
Type 2: Network LSA
Type 3: Summary LSA
Type 4: ASBR Summary LSA
Type 5: External Data LSA
Type 6: Link State Request
Type 7: Link State Acknowledgement
OSPF Type 1 Router LSA:
The Type 1 LSAs are generated by the designated router on a broadcast network and are flooded throughout the network.
OSPF Type 2 Network LSA:
The OSPF Type 2 Network LSA is for networks that are not connected to the backbone. It is used when a network has other routers in its area that are connected to the backbone.
OSPF Type 3 Summary LSA:
The Type 3 Summary LSA is a router advertisement that advertises a summary route, which is an IP prefix and the subnet mask. The Type 3 Summary LSA is different from the Type 1 and 2 LSAs because it doesn’t contain the complete routing table.
OSPF Type 4 ASBR Summary LSA:
An autonomous system boundary router (ASBR) is a router which is connected to multiple routing domains. The OSPF Type 4 ASBR Summary LSA is an LSA that advertises routes from one routing domain to another.
OSPF Type 5 External Data LSA:
The Type 5 External Data LSA is an LSA that is used by OSPF routers to advertise external routes. These external routes are advertised through a Type 1 LSA.
OSPF Type 6 Link State Request:
The OSPF Type 6 Link State Request is a type of OSPF packet that is sent by an OSPF router to request the information of a specific link. The router sends the packet to its neighbors, who then reply with an OSPF Type 7 Link State Update.
OSPF Type 7 Link State Acknowledgement:
The OSPF Type 7 Link State Acknowledgement is a link state advertisement (LSA) that is sent by an intermediate system back to the originator of the LSA. It is sent in response to a request for confirmation, usually after a change has been made to one or more LSAs.
The LSA contains the following fields:
A type field of 7;
A sequence number;
An acknowledgement number;
An acknowledgement delay time;
An IP address of the sender;
LS age field, which indicates how long ago the LSA was originated from this router.
If you would like to know more about this subject or others, leave a comment below with you questions for the folks at Functionkey, Inc.
