OSPF routing foundation 1
--The first of-link state routing protocol – OSPF concept
--OSPF area design and terminology
--OSPF neighbor relationship
There are 2 link state protocol: IsIs and OSPF
It maintains 3 tables:
- Neigbor table
- Topology table
- Routing Table
--Use Dijkstra’s Shortest Path First algorithm (SPF)
--Send triggered updates to announce network change.
--Send periodic Update on long intervals ( LS Refresh) .Link State is not sending update every 30 second like EIGRP , but send updates when there is any changes.. ( after a long interval, a router running OSPF could send the whole routing table map every 30 minutes, to make sure every router is on the same “page”).
Link state not only knows the other routers but all the road map of the entire area… That’s the biggest difference with the other type of routing..
The biggest disadvantage of lnik state is that they could be very processor intense..Distance vector only knows what the neighbor knows.
--Neighbor table:it will track all the neighbor and exchange routes with that are running ospf or isis protocol
--Topology table: (the biggest difference with link state routing protocol):Every router has a topology table that is basically a road map of every network in the area and all possible paths to get there..It’s not a route map, it’s what the neighbor has pass on.That’s why Distance vector has always been consider Routing By Rumor.
Link State knows the whole map of the entire area.Distance vector only knows the best path from the neighbor. That’s why EIGRP is more processor efficient.
Area Border Router: (ABR) Between two area . One of the router MUST be in Area “0”.All AREAS must be connected to area “0”
The point of this design is to optimize the local updates within the area.Localize updates within the specific area.
Requires hierarquical design: Different numbers of networks per area so we can do summarization
Autonomous system Boundaries Router (ASBR): The router to connect outside of your autonomus system
Understanding OSPF Neighbor relationship
Thed (ABR) and (ASBR) are the only routers that can do summarization. You can have 50 routers but they are the only one capable of doing so.
--The Router ID here will be 192.168.1.1 ( the highest active interface). If you got Loopbacks it will automatically become the router ID
The OSPF Router ID only changes when the OSPF restart or you reboot the router
It doesn’t change automatically and not often. It wait till router reboots ( maybe 8 years ) or it clean the ospf process and reset the process..
If the router ID change .. there could be problems ..very dangerous…them the ospf reboots and ospf fails between the 2 routers.
To add a interface could be dangerous because you forgort 10 years ago that you added when you reboot the router.
1.- The router –ID could be hard coded using the router –ID command
It means you could have hierarquical, them physical interfaces ( loopbacks) and above everything router-id
2.-The router add interfaces to the link state database ( dictated by the network command)
3.-Send a hello message on a chosen interface : it ‘s consider a * Down state: It says hello when trying to form a relationship
