<br> # My Thoughts - Five AS path prepends could be dropped by ISPs. - Do not use more than two AS path prepends. ## Why? (목적 - 왜 기록하는가?) ## How? (방법 - 어떻게 활용할까?) ## What? (결과 - 무엇을 창조할까?) <br> # Summary ## Best Practices using AS Path Prepending https://blog.ipspace.net/kb/tag/BGP/Filter_Excessively_Prepended_BGP_Paths/ Excessive AS-path prepending (more than five or six copies of the same AS in the AS-path) very rarely solves the path selection issues, pollutes the BGP routing tables and adversely impacts routers throughout the Internet. As an ISP cannot rely on its customers’ ability to advertise acceptable BGP prefixes, AS path access lists should be used to filter inbound BGP updates and drop excessively prepended prefixes. https://www.noction.com/blog/as-path-filtering One network operator mentioned filtering out prefixes with AS paths longer 20 hops. However, due to the rapidly declining effect of additional prepends, it may be best to avoid applying more than three prepends anyway. https://datatracker.ietf.org/doc/html/draft-ietf-grow-as-path-prepending-12 Some have added 100 or more AS Path Prepends and operators should therefore consider limiting the maximum AS-path length being accepted through aggressive filter policies. There is no need to prepend more than 5 ASs. <br> # References <br> # Links [[_MOC_2_Network]] <br> # Tags #network #protocol #routing #bgp <br>