5_Dynamic routing Flashcards
What is the main difference between distance-vector and link-state routing protocols?
Distance-vector protocols determine routes based on the distance and direction to a network without awareness of the full network topology. In contrast, link-state protocols create a complete map of the network topology and use algorithms like Dijkstra’s algorithm to determine the shortest path.
Explain the concept of “cost” in OSPF.
In OSPF, cost is a metric used to determine the best path to a destination. It is calculated as the reference bandwidth (default 100 Mbps) divided by the interface bandwidth. Lower cost indicates a more preferred path.
What is the purpose of the OSPF Link-State Database (LSDB)?
The OSPF LSDB contains all link-state information about the network, shared among routers within the same area. It is used to create a topology map and calculate the shortest path to each network.
Describe the function of passive interfaces in RIP and OSPF.
Passive interfaces are used to stop the transmission of routing updates through a specific router interface. However, the network connected to the passive interface is still advertised to other routers. This enhances security and saves bandwidth.
What are the three main components of OSPF, and what is their purpose?
Neighbor Table: Stores information about OSPF neighbors.
Topology Table: Contains the entire network topology, with all possible paths.
Routing Table: Stores the best paths used for forwarding traffic.
How does the RIP protocol determine the best path to a network?
RIP uses the hop count as its metric, where the best path is the one with the fewest number of routers (hops) between the source and destination networks.
What is an Area Border Router (ABR) in OSPF?
An ABR is a router that connects different OSPF areas. It maintains separate LSDBs for each area and exchanges routing information between them.
How does OSPF calculate and propagate changes in network topology?
OSPF uses link-state advertisements (LSAs) to share changes in topology. These updates are flooded throughout the area to ensure all routers have an updated LSDB.
What is the purpose of the “auto-cost reference-bandwidth” command in OSPF?
The command adjusts the reference bandwidth for calculating OSPF cost metrics. It must be consistent across all routers in the OSPF domain to ensure accurate path calculations.
Explain the role of a Designated Router (DR) and Backup Designated Router (BDR) in OSPF.
The DR is elected on multi-access networks to reduce routing overhead by handling the exchange of LSAs. The BDR serves as a backup, taking over if the DR fails.
How does OSPF achieve scalability using areas?
OSPF divides the network into areas. Routers within an area share detailed topology information, but only summarized routes are shared between areas. This reduces the amount of routing information exchanged and stored.
What is the significance of the metric cost in OSPF when choosing a route?
The metric cost determines the preference for a route. The path with the lowest cumulative cost (sum of costs for all links in the path) is chosen as the best route.
How are OSPF neighbors established?
OSPF neighbors are established when two routers on the same network exchange “Hello” packets, verify their parameters (e.g., area ID, timers), and synchronize their LSDBs.
Describe the key difference between RIP and OSPF in terms of network convergence.
RIP relies on periodic updates and can be slow to converge, as it uses hop count for routing decisions. OSPF converges faster due to its complete topology map and efficient use of LSAs for propagating changes.
What is the purpose of the “default route” in routing protocols like RIP and OSPF?
A default route provides a gateway of last resort, directing packets to a specific next-hop router when there is no explicit route for the destination in the routing table.
