What is Border Gateway Protocol and BGP announcements?

Border Gateway Protocol (BGP) is a routing protocol used to exchange information between routers on the internet. It enables the internet to function as a network of networks by routing traffic between different autonomous systems (ASes) across the world.

BGP announcements play a critical role in this process.

An announcement refers to the advertisement of an AS's IP address prefix to other ASes on the internet. The AS initiates an announcement by sending a BGP update message to its neighbouring ASes. This message contains information about the announced IP address prefixes, such as the AS path, next hop address, and BGP community.

When an AS receives an announcement, it adds the prefix to its routing table and propagates the announcement to its neighbouring ASes. This allows the announcement to be disseminated throughout the internet, eventually reaching all ASes that need to know about the network. By announcing its IP address prefixes, an AS is able to make its networks reachable to other ASes and enable traffic to flow between them.

BGP announcements are crucial for the global internet for several reasons. Firstly, BGP allows the internet to scale to millions of networks and billions of devices by enabling efficient routing of traffic between different ASes. Secondly, BGP enables redundant paths to be established between different ASes, ensuring that traffic can be rerouted in the event of a network outage or other disruption. Thirdly, BGP provides network operators with flexibility in implementing routing policies and configurations, giving them greater control over how traffic is routed across the internet. Lastly, BGP provides a mechanism for network operators to authenticate the source of routing information, helping to prevent unauthorised changes to routing tables and mitigating the risk of malicious attacks.