{"id":27561,"date":"2024-10-09T16:03:47","date_gmt":"2024-10-09T16:03:47","guid":{"rendered":"https:\/\/blog.lacnic.net\/?p=27561"},"modified":"2024-10-09T18:33:31","modified_gmt":"2024-10-09T18:33:31","slug":"analysis-of-bgp-prepending-in-the-lac-region-in-2024","status":"publish","type":"post","link":"https:\/\/blog.lacnic.net\/en\/analysis-of-bgp-prepending-in-the-lac-region-in-2024\/","title":{"rendered":"Analysis of BGP Prepending in the LAC Region in 2024"},"content":{"rendered":"\n

By Alejandro Acosta<\/a>, R&D Coordinator at LACNIC<\/p>\n\n\n\n

Introduction<\/strong><\/h2>\n\n\n\n

In this report, we will explore a very specific aspect of BGP tables in our region, focusing on the status of BGP prepends. We will provide a detailed review of both IPv4 and IPv6 BGP tables and share our findings. <\/p>\n\n\n\n

Commonly known as \u2018AS Path Prepending,\u2019 BGP prepending is a long-established and very popular technique designed as a key strategy for influencing route selection and optimizing an AS’s inbound and outbound traffic. It is used by all types of network operators. But how effective is this technique? Should it always be used? Are there any other options?<\/p>\n\n\n\n

History<\/strong><\/h2>\n\n\n\n

As we mentioned a few months ago in our blog post titled A Much-Needed BGP RFC: AS Path Prepending<\/a> [1], a document titled \u2018AS Path Prepending\u2019 [2] is currently being developed within the IETF, and LACNIC had the opportunity to participate and contribute to the draft. The document outlines several considerations for configuring BGP prepending. This raises the question: Are we doing things right in Latin America and the Caribbean? This report will hopefully address several concerns.<\/p>\n\n\n\n

What is AS Path Prepending?<\/strong><\/h2>\n\n\n\n

AS Path Prepending is a technique that involves repetitively adding one’s autonomous system identifier (ASN) to the list of ASs in a BGP route path (AS_PATH). Its goal is to influence route selection by making certain paths less attractive to inbound\/outbound traffic. In other words, it consists of adding our autonomous system to the AS_PATH and thus artificially \u2018lengthening the path\u2019 to a prefix on the Internet.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

In the image above, without prepends, Router A prefers to reach C via B. However, when three prepends are added by B, router A decides to reach C via D.<\/p>\n\n\n\n

Data Sources Used for This Study<\/strong><\/h2>\n\n\n\n