Which IGP Should You Choose for Fast Reconvergence and Scalability?
Question
You have been asked to use an interior gateway protocol (IGP) to design your network. You have been told that your design should allow for fast reconvergence and scalability for future growth. Which IGP would accommodate these criteria?
Answers
Explanations
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Static routing is static and not a protocol. BGP is an EGP rather than an IGP. OSPF has a faster convergence due to its link-state architecture compared to RIP, which is a distance vector protocol.
The most suitable IGP for the described criteria is Open Shortest Path First (OSPF).
OSPF is a link-state routing protocol that can handle a large network with multiple routers and complex topologies. It operates by exchanging link-state advertisements (LSAs) between routers to build a complete topology of the network, and then calculates the shortest path tree (SPT) to each destination. This process allows for fast reconvergence in the network as OSPF routers can quickly detect changes in the network and recalculate the SPT, leading to a rapid convergence time.
Furthermore, OSPF is designed to be scalable and supports variable-length subnet masks (VLSMs), which allows for efficient use of IP address space. It also allows for hierarchical design using areas, which can further enhance scalability by reducing the size of the SPF tree calculation and limiting the propagation of route updates. As a result, OSPF is widely used in large enterprise networks, internet service providers (ISPs), and data center networks.
Static routing, on the other hand, does not support automatic network updates, and each routing table entry must be manually configured. This can be time-consuming, error-prone, and challenging to manage in a large network. In contrast, a dynamic routing protocol like OSPF allows routers to automatically exchange routing information and adapt to changes in the network.
Routing Information Protocol (RIP) is an older distance-vector protocol that is less scalable and less efficient than OSPF. It has a limited hop count of 15 and can be slow to converge in large networks. Therefore, it is not recommended for modern network designs.
Border Gateway Protocol (BGP) is an exterior gateway protocol (EGP) used for routing between autonomous systems (ASes) and is not an IGP. It is designed to be scalable and support policy-based routing and route filtering. However, it is not typically used within an enterprise network as it is more suited for service provider networks and internet routing.
