Link state routing protocol is one of the two protocols (the other is distance vector routing protocol), used in packet switching networks. Link state routing uses the Dijkstra or Shortest Path First (SPF) algorithm. The protocol works as each node makes a connectivity map of the network in the form of a graph that shows where the node connects to which neighboring node. The protocol will then calculate the best logical path to each destination node and adds it to its routing table. Examples of link state routing protocols are OSPF and IS-IS.
The contrast with link state routing and distance vector routing is that link state routing shares only the information about the connectivity with its neighbors, whereas distance vector routing shares the full routing table of the node with its neighbors. Another one is that after the initial exchange of LSAs are made, link state protocols do not exchange information anymore until there is a change in the network topology. However, it will advertise all its LSAs every 30 minutes, whereas distance vector protocols sends full routing table and process it every 30 or 90 seconds. Compared to DV, LS is therefore more bandwidth and resource efficient.
The first process in creating a routing link is that the routers must be neighbors first by forming an adjacency. To form this adjacency, the routers must agree on the area number, the hello and dead timer settings, and stub area and link authentication configuration. All of this must be the same on both sides of the link or this adjacency will not be formed. The default Hello timer is 10 seconds, and the default dead timer is 40 seconds.
To check router's adjacency type the command "#show ip ospf neighbor" or "#show ip ospf interface"
After this adjacency is formed, the routers will send then Link State Updates (LSUs) which contains Link State Advertisements (LSAs). LSA contains e.g. subnet masking information. LSA will be processed by the receiving router and placed into the link state database and the SPF algorithm is applied to this database to create the OSPF routing table.
To see the database type the command: "#show ip ospf database"
LSA contains sequence numbers which will be checked upon arrival on the destination router. This router will then compare its sequence number (from the previous LSA) to the current LSA. There are 3 possible actions that can happen:
1. If the sequence number is the same, the LSA is ignored by the receiving router
2. If the sequence number is lower than the sequence number the router has, than the router will ignore the update and sends the LSU back to the sending router.
3. If the sequence number is higher, the LSA is accepted an will be added to its database. Afterwards, the receiving router will send an LSA acknowledgment back to the sending router. It will the flood that LSA and will run the SPF algorithm to update its own routing table and holds therefore the most updated route.
To config OSPF type the command:
(config)#router ospf
(config-router)#network area
(config-router)#network area
Configure it on both ends of the link and an adjacency should be formed. We can show it using : #show ip ospf neighbor
To see the ospf database: #show ip ospf database
To see the interface running ospf: #show ip ospf interface
-- 3 Januari 2011 --
The contrast with link state routing and distance vector routing is that link state routing shares only the information about the connectivity with its neighbors, whereas distance vector routing shares the full routing table of the node with its neighbors. Another one is that after the initial exchange of LSAs are made, link state protocols do not exchange information anymore until there is a change in the network topology. However, it will advertise all its LSAs every 30 minutes, whereas distance vector protocols sends full routing table and process it every 30 or 90 seconds. Compared to DV, LS is therefore more bandwidth and resource efficient.
The first process in creating a routing link is that the routers must be neighbors first by forming an adjacency. To form this adjacency, the routers must agree on the area number, the hello and dead timer settings, and stub area and link authentication configuration. All of this must be the same on both sides of the link or this adjacency will not be formed. The default Hello timer is 10 seconds, and the default dead timer is 40 seconds.
To check router's adjacency type the command "#show ip ospf neighbor" or "#show ip ospf interface"
After this adjacency is formed, the routers will send then Link State Updates (LSUs) which contains Link State Advertisements (LSAs). LSA contains e.g. subnet masking information. LSA will be processed by the receiving router and placed into the link state database and the SPF algorithm is applied to this database to create the OSPF routing table.
To see the database type the command: "#show ip ospf database"
LSA contains sequence numbers which will be checked upon arrival on the destination router. This router will then compare its sequence number (from the previous LSA) to the current LSA. There are 3 possible actions that can happen:
1. If the sequence number is the same, the LSA is ignored by the receiving router
2. If the sequence number is lower than the sequence number the router has, than the router will ignore the update and sends the LSU back to the sending router.
3. If the sequence number is higher, the LSA is accepted an will be added to its database. Afterwards, the receiving router will send an LSA acknowledgment back to the sending router. It will the flood that LSA and will run the SPF algorithm to update its own routing table and holds therefore the most updated route.
To config OSPF type the command:
(config)#router ospf
(config-router)#network
(config-router)#network
Configure it on both ends of the link and an adjacency should be formed. We can show it using : #show ip ospf neighbor
To see the ospf database: #show ip ospf database
To see the interface running ospf: #show ip ospf interface
-- 3 Januari 2011 --
No comments:
Post a Comment