OSPF which is a Link state and Open standards routing protocol. As we all are aware of Routing protocol types, that is Link state and Distance vector. Also, there are some routing protocols that are vendor-proprietary and some are industry standards or open standards. It is adopted by most organizations for their Data Centre and WAN Networks.
What is Link State Protocol
Routing Protocol that exchanges information about the state of their directly connected links with all other routers in the network, such as OSPF and IS-IS.
Some Link state features are:
- Exchange information about the state of their directly connected links with all other routers in the network.
- Each router creates a detailed map of the network’s topology and calculates the shortest path to reach each destination.
- Link-state protocols have a more comprehensive view of the network topology and converge faster than distance vector protocols
What is OSPF Protocol
It stands for Open Shortest Path First and it is a link state Open Standard routing protocols.
As this name says.
Open: Its Open Standards Link State Routing Protocols which can be configured at any vendor/OEM.
Shortest Path First: It identifies the shortest path to reach destination based on some matrices which we discuss.
- Unlimited hope router
- Identical databases built for all router and every router
- Open standards
- Security point of view—neighbor authentication must between two neighbours
- multiple area concepts
- Only work on trigger base, only send if required.
- Matric is cost
OSPF characteristics:
- It is Link State Protocol.
- It employs a hierarchical network design using Areas.
- It will form neighbor relationships with adjacent routers in the same Area.
- Instead of advertising the distance to connected networks, it advertises the status of directly connected links using Link-State Advertisements (LSAs).
- It sends updates (LSAs) when there is a change to one of its links, and will only send the change in the update. LSAs are additionally refreshed every 30 minutes.
- It traffic is multicast either to address 224.0.0.5 (all routers) or 224.0.0.6 (all Designated Routers).
- It uses the Dijkstra Shortest Path First algorithm to determine the shortest path.
- It is a classless protocol, and thus supports VLSMs.
- It supports only IP routing
- It has an administrative distance is 110.
- OSPF uses cost as its metric, which is computed based on the bandwidth of the link. It has no hop-count limit
The OSPF process builds and maintains three separate tables:
- A neighbor table – contains a list of all neighbouring routers.
- A topology table – contains a list of all possible routes to all known networks within an area.
- A routing table – contains the best route for each known network.
5-OSPF Packets for neighbor Adjacencies
- Hello—to build neighborship and neighbor table
- DBD (Database)— by this packet neighbor update and share their database with other neighbours to create topology table. If any neighbor has partial or missing information then they update their database by this OSPF packet.
- LSR (Link State Request)—Router will send a request to neighbor router for missing network details in form of link state request.
- LSU (Link State Update)— Neighbor Router will share the request network details / update with requestor router in form of link state update packet which is contain LSA info. Based on these routers will updates their topology and routing table run SPF algorithm.
- LSACK (Link State Ack)- Requestor Router will send an Ack to neighbor router for receiving the updates/LSA.
Convergence Time— Time consume by a router to complete routing update process will be count as convergence time.
OSPF Process ID and Router ID
- Process ID is a unique id which make separation of different instances on a router.
- To start a process on your router, it needs a 32bit IP address to select router ID.
- Router ID is router identification in overall topology. It just like a router name.
- RID is a 32-bit dotted decimal format and it can be any num. it can be 0.0.0.1 or 1.1.1.1
- RID IP or Int should be up during router selection
- Once RID selected then if we shut down the Int then it will not remove until unless router will not reload. If reload then RID will change and then all process will need to run SFP to select RID and converges process. So, It is recommends to give manual RID.
- If we select RID manually then it never removed.
- No need to route RID IP address in routing table, it is not for communication only for identification.
- if we run two process ID then it needs two different RID.
We can give RID manually like (router ospf 100—-> router-ID 0.0.0.1). If not manually, then ospf select the RID with auto selection criteria which is:
- 1st preference is Loopback Address.
- 2nd preference is highest loopback if router have more than two loopback IP.
- 3rd preference is physical interface IP,
- 4th preference highest interface IP if more than two int IP.
OSPF Neighbours discovery process
Routers will only become neighbours if the following parameters within a Hello packet are identical on each router:
- Area ID
- Area Type (stub, NSSA, etc.)
- Prefix
- Subnet Mask
- Hello Interval and keepalive on periodic interval in every 10 sec. after 40 sec if hello not recd it will dead
- Network Type (broadcast, point-to-point, etc.)
- Authentication should be match.
- Priority value should be there for DR/BDR selection
- Use multicast add 224.0.0.5, and 224.0.0.6 for DR/BDR
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FAQ
Q. What is Link State routing protocols?
A. Routing Protocol that Exchange information about the state of their directly connected links with all other routers in the network, such as OSPF and IS-IS.
Q. Is OSPF Links state or Distance Vector routing protocols?
A. OSPF is Link State routing protocols.
Q. Is OSPF Cisco Proprietary routing Protocols?
A. No, OSPF is open standards Routing protocol.
Q. OSPF stands for?
A. OSPF stand for Open Shortest Path First.
Q. What are 5 OSPF Packet types
A. 5 OSPF Packet types are: Hello, DBD, LSR, LSU, LSACK
