In this tutorial, we\u2019ll go over the basics of BGP (Border Gateway Protocol) and what makes it different from other routing protocols. If you\u2019re just getting started with routing or trying to understand how large networks communicate over the internet, this will help build a solid foundation.<\/p>\n\n\n\n
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1. What is a Routing Protocol?<\/strong><\/p>\n\n\n\n A routing protocol<\/strong> is used by routers to learn about the networks around them and to decide the best path to reach a destination. Its main functions include:<\/p>\n\n\n\n There are different types of routing protocols, and each one is used for specific scenarios. BGP is one of them\u2014but it works differently from most others.<\/p>\n\n\n\n 2. AS, IGP, and EGP \u2013 The Context of BGP<\/strong><\/p>\n\n\n\n Before we understand BGP, we need to understand what an Autonomous System (AS)<\/strong> is.<\/p>\n\n\n\n Now, routing protocols are broadly classified into two types:<\/p>\n\n\n\n Border Gateway Protocol (BGP) \u00a0is the only EGP in use today.<\/strong> that routes data between different autonomous systems<\/strong>\u00a0on the internet. RFC 4271 specifies BGP, highlighting its crucial role in maintaining the global internet\u2019s vast, interconnected landscape.<\/p>\n\n\n\n 3. What Makes BGP Different?<\/strong><\/p>\n\n\n\n BGP is designed for very large and complex networks, like the internet. It\u2019s different from traditional IGPs in two important ways:<\/p>\n\n\n\n a) Policy-Based Routing<\/strong><\/p>\n\n\n\n Unlike protocols like OSPF that choose the shortest path based only on cost or metrics, BGP allows administrators to define routing policies<\/strong>.<\/p>\n\n\n\n You can choose routes based on business rules, security, performance, or agreements between organizations.<\/p>\n\n\n\n Imagine BGP as the internet\u2019s diplomatic mediator, managing how different countries (or autonomous systems) interact to route data. It doesn\u2019t just find the shortest path; it chooses the best route based on a set of agreed-upon rules.<\/p>\n\n\n\n b) Scalability<\/strong><\/p>\n\n\n\n BGP can handle hundreds of thousands of routes<\/strong>, making it ideal for service providers and internet backbones. Protocols like OSPF and EIGRP are not designed to scale to that level.<\/p>\n\n\n\n 4. BGP Peering \u2013 How Routers Communicate<\/strong><\/p>\n\n\n\n Routers that run BGP don\u2019t automatically discover neighbors like in OSPF. Instead, they form manual connections called BGP peerings or BGP sessions.<\/p>\n\n\n\n There are two types of BGP peerings:<\/p>\n\n\n\n The purpose of peering is to exchange routing information. Each peer advertises what networks it knows, and BGP decides how to reach them.<\/p>\n\n\n\n Unlike some other protocols, BGP does not require peers to be directly connected physically. Since it uses unicast IP addresses to establish TCP sessions, BGP peerings can be formed even over multiple hops. This is quite common in iBGP, where peers may be several routers apart.<\/p>\n\n\n\n However, in eBGP, direct connection is typically preferred unless additional configurations (like TTL settings or loopbacks) are used.<\/p>\n\n\n\n 5. Path Vector Protocol and Attributes<\/strong><\/p>\n\n\n\n BGP is a path vector protocol<\/strong>, meaning it doesn\u2019t just say \u201cI know a path,\u201d but it also tells you how it got there<\/strong>.<\/p>\n\n\n\n Each BGP route comes with a set of path attributes<\/strong> that help routers decide the best path. These attributes include:<\/p>\n\n\n\n This is what allows BGP to support complex routing decisions across the internet.<\/p>\n\n\n\n 6. Why BGP Uses TCP<\/strong><\/p>\n\n\n\n BGP uses TCP (port 179)<\/strong> to establish and maintain connections between peers.<\/p>\n\n\n\n Using TCP provides several advantages:<\/p>\n\n\n\n Because of this, BGP can focus purely on routing logic, and let TCP handle reliability.<\/p>\n\n\n\n Summary Table<\/strong><\/p>\n\n\n\n Introduction to BGP \u2013 The Backbone of Internet Routing In this tutorial, we\u2019ll go over the basics of BGP (Border Gateway Protocol) and what makes it different from other routing protocols. If you\u2019re just getting started with routing or trying to understand how large networks communicate over the internet, this will help build a solid […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"wp-custom-template-post-with-sidebar2","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[103,66],"tags":[104,112,113,110,108,109,111,107,114,106,115],"class_list":["post-219","post","type-post","status-publish","format-standard","hentry","category-bgp","category-routing","tag-bgp","tag-bgp-keepalive-packet","tag-bgp-notification-packet","tag-bgp-open-packet","tag-bgp-packet-types","tag-bgp-protocol","tag-bgp-update-packet","tag-features-of-bgp","tag-how-bgp-is-different","tag-what-is-bgp","tag-why-bgp-is-used-as-egp"],"yoast_head":"\n\n
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![\"Illustration](\"https:\/\/i0.wp.com\/www.zframez.com\/articles\/wp-content\/uploads\/2024\/07\/BGP-packet.png?resize=1024%2C433&ssl=1\")
\n\n\n\nConcept<\/strong><\/td> Description<\/strong><\/td><\/tr><\/thead> Routing Protocol<\/td> Allows routers to exchange and update route information<\/td><\/tr> AS (Autonomous System)<\/td> A group of networks under one organization with a unique ASN<\/td><\/tr> IGP<\/td> Protocols used within an AS (e.g., OSPF, EIGRP)<\/td><\/tr> EGP<\/td> Protocol used between ASes (BGP)<\/td><\/tr> BGP<\/td> A scalable, policy-based EGP used on the internet<\/td><\/tr> iBGP<\/td> Peering between routers within the same AS<\/td><\/tr> eBGP<\/td> Peering between routers in different ASes<\/td><\/tr> Path Vector<\/td> BGP uses path attributes to make routing decisions<\/td><\/tr> TCP<\/td> BGP uses TCP for reliable communication on port 179<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
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