CISCO - Routing Protocols (RIP, OSPF, and EIGRP)
Routing protocols allow networking devices, such as routers, to communicate with one another and share information over the networks. Cisco, a networking hardware industry leader, actively uses different routing protocols in their devices to achieve effective routing. Some of the main routing protocols commonly used in Cisco devices are as follows −
Routing Information Protocol (RIP)
Routing Information system (RIP) is a distance-vector routing protocol that is most widely used in small and medium-sized networks. It broadcasts routing updates at regular intervals (every 30 seconds), and each router shares its whole routing table with neighboring routers. If a device does not get an update from another device for 180 seconds or more, the receiving device considers the routes served by the non-updating device is unusable. If there is still no update after 240 seconds, the device deletes all routing table entries for the non-updating device.
Hence, the Routing Information Protocol transmits routing-update messages on a regular basis and whenever the network topology changes. When a device receives a RIP routing update containing modifications to an item, it updates its routing table to reflect the new route. The metric value of the path is increased by one, and the sender is identified as the next hop. RIP devices keep only the best route (the one with the lowest metric value) to a destination. After upgrading its routing database, the device instantly starts propagating RIP routing updates to notify other network devices about the change. These updates are sent apart from the regularly scheduled updates that RIP devices send.
Overall, the protocol's fundamental criterion for determining the optimum route is hop count, with each hop representing a router on the road to the destination. However, RIP has a maximum hop count of 15, therefore any route with more than 15 hops is considered unreachable. This makes RIP appropriate for smaller, less complex networks where simplicity and ease of configuration are important.
RIP Routing Metric
The Routing Information Protocol (RIP) uses a single routing metric to calculate the distance between the source and destination networks. Each hop in a path from source to destination is allocated a hop-count value, which is normally one. When a device receives a routing update that includes a new or modified destination network entry, it adds 1 to the metric value specified in the update and adds the network to the routing table. The sender's IP address is used for the next step. If an interface network is not defined in the routing table, it will not be advertised in subsequent RIP updates.
OSPF
Cisco's OSPF (Open Shortest Path First) is a popular link-state routing technology for big and complicated networks. It efficiently determines the shortest path for data packets using the Dijkstra method, with network bandwidth as the major criteria for determining route cost. OSPF differentiates itself by its hierarchical design, which separates a network into multiple areas to reduce the amount of routing information transmitted between routers. OSPF divides the network into areas to optimize routing and minimize traffic. This hierarchical approach improves scalability.
Area 0 (Backbone Area) − The core of an OSPF network; all areas must connect to Area 0.
Non-backbone Areas − These connect to the backbone and help to localize routing information.
Therefore; OSPF works in a hierarchical structure by splitting the network into areas to improve scalability and reduce routing costs. The backbone, designated as Area 0, connects all other areas in the OSPF domain, allowing for efficient data transfer across the network.
Routers are divided into three groups based on their roles in the OSPF topology: internal routers (routers with interfaces in the same area), Area Border Routers (ABRs) that connect several areas, and Autonomous System Boundary Routers (ASBRs), which connect OSPF to other routing protocols. This structured method reduces superfluous traffic while improving the network's overall performance.
This method decreases overhead while also improving scalability, making OSPF suited for enterprise-level networks. OSPF supports Variable Length Subnet Masking (VLSM), which allows for more precise IP addressing and efficient use of address space.
Cisco's OSPF has fast convergence capabilities, which allows the network to stabilize quickly whenever topological change occurs, such as a link failure. This is critical for ensuring network availability and reducing downtimes. OSPF employs multicast for routing updates, which reduces wasted traffic. It also has route authentication features to secure routing changes and keep unauthorized devices from inserting harmful routes into the network. With these capabilities, OSPF combines flexibility and resilience, making it an essential choice for enterprises with big, dynamic networks that demand efficient, reliable routing.
One of OSPF's primary advantages is its ability to support variable-length subnet masking (VLSM) and Classless Inter-Domain Routing (CIDR), which allows for more efficient use of IP address space. Its rapid convergence and responsiveness to network changes make it ideal for enterprise and large-scale networks. However, OSPF is more difficult to establish and maintain than simpler protocols like RIP, necessitating more resources such as memory and CPU power to manage the LSDB and calculate the shortest paths. Despite this, OSPF remains a popular protocol due to its durability, scalability, and ability to manage dynamic network situations effectively.
OSPF Metric (Cost) − OSPF determines the optimum route using a parameter called cost, which is inversely proportional to bandwidth.
EIGRP
The Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco advanced routing protocol used in computer networks to automate routing. It is designed specifically to support routers to share information more efficiently than older protocols like RIP (Routing Information Protocol), but with less overhead than link-state protocols like OSPF (Open Shortest Path First). Cisco's EIGRP is a dynamic routing protocol that combines features of distance-vector and link-state protocols. Unlike traditional distance-vector protocols like RIP, which broadcast whole routing tables on a regular basis, EIGRP sends updates only when the network changes, and impacted routers. This method reduces bandwidth utilization and assures faster convergence. EIGRP also employs the Diffusing Update Algorithm (DUAL), which facilitates loop-free routing and quick recovery from link failures, resulting in little network downtime.
EIGRP was one of the proprietary to Cisco, it became an open standard in 2013, enabling for more usage in multivendor networks. Its support for classless inter-domain routing (CIDR) and variable-length subnet masking (VLSM) makes it an adaptable protocol for current IP addressing. EIGRP's ability to summarize routes and execute automatic or manual route aggregation reduces routing table size, which improves scalability.
One of EIGRP's primary features is the use of a composite measure for route selection that considers bandwidth, delay, load, and reliability. It prioritizes bandwidth and delay, but network administrators can tailor the metrics to meet specific performance requirements. Additionally, EIGRP enables equal and unequal-cost load balancing; offering network engineers the ability to distribute traffic across several pathways. This characteristic is very useful in complex, large-scale networks, as it improves redundancy and speed.
EIGRP Metric
Cisco's EIGRP employs a sophisticated metric system to find the optimal path for routing data across a network. Unlike simpler protocols that rely on a single metric, such as hop count (as in RIP), EIGRP determines its measure using a number of parameters, making it more adaptive to different network environments. The default metric formula for EIGRP considers bandwidth and delay, but it can additionally incorporate other metrics such as load, reliability, and Maximum Transmission Unit (MTU), giving administrators more control over route selection. The EIGRP metric formula includes primary components like bandwidth and delay.
Bandwidth is the minimum bandwidth (in kilobits per second) along the way to the destination, whereas delay is the total delay (in tens of microseconds) between source and destination.