When you click on a website link in your browser, the server request has to bounce around from router to router until it reaches the web server. BGP is the protocol that allows all this to happen seamlessly. BGP provides reachability information between Autonomous Systems (ASes). It’s not unlike international shipping rules for mail.
What is BGP?
The routing protocol that powers the internet is called BGP. It allows network devices to share routing and reachability information between networks across the internet, ensuring that data packets travel along the best path from source to destination. Without BGP, it would be impossible for ISPs and large companies to connect their networks with the rest of the world. Every BGP router keeps track of all the routes to reach any other network on the internet in a routing table. Each course is described by its next hop and interface and attributes (such as routing policy and cost) determining how data should be sent to a specific destination network. BGP routers also communicate with other routers in the same autonomous system (AS) to learn about routes not advertised by any other AS.
Each router starts a session with another BGP-enabled router by sending a Message Transfer Protocol (MTP) message to the other device to exchange routing information. Once the MTP connection is established, the router enters an OpenSent state. This short-lived state communicates that the router wants to begin trading routing information with the other BGP-enabled device. After entering this state, the router waits for an MTP keepalive message from the other device. If the keepalive is not received within a specific time frame, the router exits the OpenSent state and enters an Idle state.
How is BGP implemented?
But really, how does BGP work? BGP has been likened to the postal service of the internet, delivering data packets from one network to another. Configuring is more complex than other routing protocols because it emphasizes security and scalability more. But this intricate design helps it deliver the redundancy and scalability required for internet service provider networks, wide area networks, and infrastructure-as-a-service environments.
Each BGP router maintains a routing information base (RIB) that stores data on how to reach each network on the internet. Its peers communicate this information to each other via Update messages that contain route information and path attributes. These include an autonomous system number (ASN), a cost, a local preference, and other features that help select the best paths to networks.
Routers in the same autonomous system can advertise routes to each other, while those in different autonomous systems must only advertise courses they have added. It is to prevent routing loops that can cause traffic congestion and disruption. BGP also has a feature called route flap damping that helps mitigate this problem.
A BGP session starts in the OpenSent state and moves to the OpenConfirm state when its peer receives an update message. In this state, the RIB is updated, and the connection is set to be established. If the RIB isn’t updated or an error occurs, the relationship returns to the Idle state.
What is BGP’s role in digital transmissions?
BGP is one of the most essential elements that make the internet work. It facilitates data routing across multiple networks and provides redundancy by enabling routers to quickly adapt and send packets through another connection if the original one fails. Through network connections, BGP also allows organizations to prioritize and steer traffic based on policies and preferences. It enables organizations to maximize network performance and ensure efficient data transmissions. BGP exchanges routing information among directly connected neighbor interfaces, known as peers. This information is stored in the BGP routing information base (RIB) and continually updated. It allows quick route changes and enables the system to handle significant network traffic.
Routers must send open messages containing essential data, such as autonomous systems (AS) identifiers. Then, they must complete a three-way TCP handshake to initiate the process of building a connection. Once they’ve completed the handshake, they move to Connect state. From there, they will continue to communicate with each other to update the RIB. BGP peering sessions can utilize communities to set various attributes on prefixes to influence how outbound traffic is distributed across their network. Some examples include weight (used to measure route priority) and local preference (used to determine which paths to take). In addition, BGP supports multi-homed connectivity, allowing an organization to connect to multiple ISPs simultaneously for redundancy or efficiency.
Why is BGP important?
The internet works thanks to BGP, which is responsible for looking at all the possible routes data could travel and picking the fastest and cheapest. It also ensures that network prefixes, the unique identifiers of networks on the internet, are correctly routed. To ensure that BGP can choose the best paths, it constantly adjusts its routing tables to account for new networks built or taken down and routers that change their state. It can lead to a cycle of routing announcements and withdrawals called route flapping that can cause network congestion.
As the number of networks connected grew, the global routing table size quickly became too large for some older routers to handle, leading to slow performance and potential outages. In addition, it can take a long time for changes in one network to propagate throughout all other connected networks. To address this, BGP uses an algorithm to determine the most efficient routing path for each destination by comparing the cost of each available course and selecting the one with the lowest price. The algorithm considers various factors, including the distance from the source to the destination, traffic on each route, and other considerations. BGP also considers any specific routing policies the network operator sets to ensure the chosen path is optimal for its needs.
