Routing Between Networks - PDF

Routing Between Networks How does network routing work?  What is a routing table? A routing table is a record within every router. It informs which path a packet should take. Each table comprises a list of destinations – IP address prefixes to which th...

Routing Between Networks How does network routing work?  What is a routing table? A routing table is a record within every router. It informs which path a packet should take. Each table comprises a list of destinations – IP address prefixes to which the packet can be forwarded.  Routers refer to routing tables to determine the best path between computers Obviously, because computer networking is never quite complicated enough, there are also two kinds of routing tables: static and dynamic. Static routing tables are set by a network administrator and don’t change unless the administrator updates them. This means that static routing tables do not respond to network conditions. Usually, only smaller networks use static routing tables, as they quickly become unhelpful at scale. Dynamic routing tables, on the other hand, can update themselves automatically. Using dynamic routing protocols, they can proactively predict the shortest and fastest routes to send data packets.  What is Routing? Routing is the process of path selection in any network. A computer network is made of many machines, called nodes, and paths or links that connect those nodes. Communication between two nodes in an interconnected network can take place through many different paths. Routing is the process of selecting the best path using some predetermined rules.  What are the main routing protocols? A routing protocol is a set of rules that specify how routers identify and forward packets along a network path. Routing protocols are grouped into two distinct categories: interior gateway protocols and exterior gateway protocols. Interior gateway protocols work best within an autonomous system—a network administratively controlled by a single organization. External gateway protocols better manage the transfer of information between two autonomous systems.  IP: The Internet Protocol (IP) specifies the origin and destination for each data packet. Routers inspect each packet's IP header to identify where to send them. BGP: The Border Gateway Protocol (BGP) routing protocol is used to announce which networks control which IP addresses, and which networks connect to each other. (The large networks that make these BGP announcements are called autonomous systems.) BGP is a dynamic routing protocol.  OSPF: The Open Shortest Path First (OSPF) protocol is commonly used by network routers to dynamically identify the fastest and shortest available routes for sending packets to their destination. RIP: The Routing Information Protocol (RIP) uses "hop count" to find the shortest path from one network to another, where "hop count" means number of routers a packet must pass through on the way. (When a packet goes from one network to another, this is known as a "hop.")  What are the types of routing? Static routing In static routing, a network administrator uses static tables to manually configure and select network routes. Static routing is helpful in situations where the network design or parameters are expected to remain constant. The static nature of this routing technique comes with expected drawbacks, such as network congestion. While administrators can configure fallback paths in case a link fails, static routing generally decreases the adaptability and flexibility of networks, resulting in limited network performance. Dynamic routing In dynamic routing, routers create and update routing tables at runtime based on actual network conditions. They attempt to find the fastest path from the source to the destination by using a dynamic routing protocol, which is a set of rules that create, maintain, and update the dynamic routing table. The biggest advantage of dynamic routing is that it adapts to changing network conditions, including traffic volume, bandwidth, and network failure.  Interior gateway protocols These protocols assess the autonomous system and make routing decisions based on different metrics, such as the following: Hop counts, or the number of routers between the source and the destination Delay, or the time taken to send the data from the source to the destination Bandwidth, or the link capacity between the source and the destination  The following are some examples of interior gateway protocols. Routing Information Protocol The Routing Information Protocol (RIP) relies on hop counts to determine the shortest path between networks. RIP is a legacy protocol that no one uses today because it does not scale well for larger network implementation. Open Shortest Path First protocol The Open Shortest Path First protocol (OSPF) collects information from all other routers in the autonomous system to identify the shortest and fastest route to a data packet’s destination. You can implement OSPF using various routing algorithms or computer processes. External gateway protocols The Border Gateway Protocol (BGP) is the only external gateway protocol. Border Gateway Protocol BGP defines communication over the internet. The internet is a large collection of autonomous systems all connected together. Every autonomous system has autonomous system number (ASN) that it obtains by registering with the Internet Assigned Numbers Authority. BGP works by keeping track of the closest ASNs and mapping destination addresses to their respective ASNs.  What are routing algorithms? Routing algorithms are software programs that implement different routing protocols. They work by assigning a cost number to each link; the cost number is calculated using various network metrics. Every router tries to forward the data packet to the next best link with the lowest cost.  The following are some example algorithms. Distance Vector Routing The Distance Vector Routing algorithm requires all routers to periodically update each other about the best path information they have found. Each router sends information about the current assessment of the total cost to all known destinations. Eventually, every router in the network discovers the best path information for all possible destinations. Link State Routing In Link State Routing, every router discovers all other routers in the network. Using this information, a router creates a map of the complete network and then calculates the shortest path for any data packet.  How has routing evolved? Routing has evolved to meet the requirements of advances in network technology. Routing is no longer just about switching data packets between autonomous systems and the internet. We now have cloud infrastructure with computing resources and hardware hosted by third-party cloud providers. These cloud resources are connected virtually to create a virtual network of resources that businesses can use to host and run applications. Many organizations now have hybrid networks that consist of both on-premises networks with internal hardware and cloud networks. Routers must route traffic between these internal networks, the internet, and the cloud.  What is cloud routing? Cloud routing dynamically manages connections between two virtual cloud networks or between a cloud network and an on-premises network using the Border Gateway Protocol (BGP). Cloud routing adapts automatically to changing network conditions in the cloud. A cloud router—software that virtualizes the functions of a router—facilitates cloud routing. What is DNS routing? DNS, or the Domain Name System, translates human-readable domain names to machine-readable IP addresses (for example, 192.0.2.44). The data that maps this name information to machine information is stored separately on DNS servers. Before sending data to any website, routers must communicate with the DNS server to identify the exact machine address for the data packets. DNS server communication can become a bottleneck, especially when many users want to visit a website at the same time. DNS routing refers to the various routing strategies and algorithms that manage communication with the DNS server. Various strategies, such as latency-based routing and geographic location–based routing, help manage the DNS server communication load.