What are three characteristics of the OSPF routing protocol? (Choose three)
Can you score high marks in this quiz with these CCNA - OSPF questions and answers? In the world of networking, the Open Shortest Path First (OSPF) routing protocol for IP networks uses a link-state routing algorithm and is classed as an interior gateway protocol. Further your knowledge of the OSPF for your CCNA certification by answering the following questions. Wish you the best of luck! Let us go now! Show OSPF (Open Shortest Path First) is a link state routing protocol. Because it is an open standard, it is implemented by a variety of network vendors. OSPF will run on most routers that doesn’t necessarily have to be Cisco routers (unlike EIGRP which can be run only on Cisco routers). Here are the most important features of OSPF:
Routers running OSPF have to establish neighbor relationships before exchanging routes. Because OSPF is a link state routing protocol, neighbors don’t exchange routing tables. Instead, they exchange information about network topology. Each OSPF router then runs SPF or Dijkstra algorithm to calculate the best routes and adds those to the routing table. Because each router knows the entire topology of a network, the chance for a routing loop to occur is minimal. Each OSPF router stores routing and topology information in three tables:
OSPF neighborsOSPF routers need to establish a neighbor relationship before exchanging routing updates. OSPF neighbors are dynamically discovered by sending Hello packets out each OSPF-enabled interface on a router. Hello packets are sent to the multicast IP address of 224.0.0.5. The process is explained in the following figure: Routers R1 and R2 are directly connected. After OSPF is enabled both routers send Hellos to each other to establish a neighbor relationship. You can verify that the neighbor relationship has indeed been established by typing the show ip ospf neighbors command. R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 2.2.2.2 1 FULL/DR 00:00:30 192.168.0.2 FastEthernet0/0
In the example above, you can see that the router-id of R2 is 2.2.2.2. Each OSPF router is assigned a router ID. A router ID is determined by using one of the following: 1. using the router-id command under the OSPF process. The following fields in the Hello packets must be the same on both routers in order for routers to become neighbors:
By default, OSPF sends hello packets every 10 second on an Ethernet network (Hello interval). A dead timer is four times the value of the hello interval, so if a routers on an Ethernet network doesn’t receive at least one Hello packet from an OSPF neighbor for 40 seconds, the routers declares that neighbor to be down. OSPF neighbor statesBefore establishing a neighbor relationship, OSPF routers need to go through several state changes. These states are explained below. 1. Init state – a router has received a Hello message from the other OSPF router OSPF areasOSPF uses the concept of areas. An area is a logical grouping of contiguous networks and routers. All routers in the same area have the same topology table, but they don’t know about routers in the other areas. The main benefits of creating areas is that the size of the topology and the routing table on a router is reduced, less time is required to run the SPF algorithm and routing updates are also reduced. Each area in the OSPF network has to connect to the backbone area (area 0). All router inside an area must have the same area ID to become OSPF neighbors. A router that has interfaces in more than one area (area 0 and area 1, for example) is called Area Border Router (ABR). A router that connects an OSPF network to other routing domains (EIGRP network, for example) is called Autonomous System Border Router (ASBR). NOTE
To better understand the concept of areas, consider the following example. All routers are running OSPF. Routers R1 and R2 are inside the backbone area (area 0). Router R3 is an ABR, because it has interfaces in two areas, namely area 0 and area 1. Router R4 and R5 are inside area 1. Router R6 is an ASBR, because it connects OSPF network to another routing domain (an EIGRP domain in this case). If the R1’s directly connected subnet fails, router R1 sends the routing update only to R2 and R3, because all routing updates all localized inside the area. NOTE LSA, LSU and LSRThe LSAs (Link-State Advertisements) are used by OSPF routers to exchange topology information. Each LSA contains routing and toplogy information to describe a part of an OSPF network. When two neighbors decide to exchange routes, they send each other a list of all LSAa in their respective topology database. Each router then checks its topology database and sends a Link State Request (LSR) message requesting all LSAs not found in its topology table. Other router responds with the Link State Update (LSU) that contains all LSAs requested by the other neighbor. The concept is explained in the following example: After configuring OSPF on both routers, routers exchange LSAs to describe their respective topology database. Router R1 sends an LSA header for its directly connected network 10.0.1.0/24. Router R2 check its topology database and determines that it doesn’t have information about that network. Router R2 then sends Link State Request message requesting further information about that network. Router R1 responds with Link State Update which contains information about subnet 10.0.1.0/24 (next hop address, cost…). Download our Free CCNA Study Guide PDF for complete notes on all the CCNA 200-301 exam topics in one book. We recommend the Cisco CCNA Gold Bootcamp as your main CCNA training course. It’s the highest rated Cisco course online with an average rating of 4.8 from over 30,000 public reviews and is the gold standard in CCNA training: Which is a feature characteristics of OSPF?Key features of OSFP
OSPF is an interior gateway protocol (IGP). It runs within a single routing domain, such as an autonomous system (AS). It uses a concept called areas, to optimize network traffic and simplify administration. It uses Dijkstra's algorithm to compute the shortest route to each destination.
What are the three categories of OSPF operations?OSPF is a link-state protocol based on the open standard. At a high level, OSPF operation consists of three main elements: neighbor discovery, link-state information exchange, and best-path calculation.
What are the characteristics of routing protocols?Routing Protocol Characteristics. Believability of a Route. ... . Metrics. ... . Interior Versus Exterior Gateway Protocols. ... . Route Advertisement Method. ... . Distance Vector. ... . Link State.. What is a routing protocol briefly describe about any 3 types of routing protocol?The Routing protocols that are used to calculate paths are distant vector routing, link-state vector routing, and path-vector routing. Each router in distance vector routing has a route distance to a destination stored in the routing table. This information is gathered from the neighboring node.
|