# Understanding multiple routes from same ASN

DevFeed: [Understanding multiple routes from same ASN](<https://devfeed.tech/articles/understanding-multiple-routes-from-same-asn-39769.md>)

Original publisher: [Read original article](<https://anuragbhatia.com/post/2025/12/understanding-multiple-routes-from-same-asn/>)

Published: 2025-12-01T18:54:58Z

Content type: article

Language: en

Sources: [Personal blog of Anurag Bhatia](<https://devfeed.tech/sources/personal-blog-of-anurag-bhatia.md>)

Topics: [networking](<https://devfeed.tech/topics/networking.md>), [Routing (disambiguation)](<https://devfeed.tech/topics/routing.md>), [Networks](<https://devfeed.tech/topics/networks.md>), [Network](<https://devfeed.tech/topics/network.md>)

Tags: [algorithm](<https://devfeed.tech/tags/algorithm.md>), [as174](<https://devfeed.tech/tags/as174.md>), [as3257](<https://devfeed.tech/tags/as3257.md>), [as3356](<https://devfeed.tech/tags/as3356.md>), [as6453](<https://devfeed.tech/tags/as6453.md>), [as9498](<https://devfeed.tech/tags/as9498.md>), [bgp](<https://devfeed.tech/tags/bgp.md>), [cisco](<https://devfeed.tech/tags/cisco.md>), [ipv6](<https://devfeed.tech/tags/ipv6.md>), [router](<https://devfeed.tech/tags/router.md>), [routing](<https://devfeed.tech/tags/routing.md>), [trace](<https://devfeed.tech/tags/trace.md>)

## AI overview

This article explains why the same autonomous system can select different routes to the same prefix. Using examples involving AS3257 and AS3356, it shows that different routers and observation points may choose different best paths according to BGP's route-selection process.

## Source excerpt

A while back bgp.he.net added the feature of a live route propagation graph for a given prefix. Besides being near real-time, it is also specific to a prefix, e.g let's look up for 2401:4900:87f0::/44 (Airtel mobility - 5G prefix): https://bgp.he.net/net/2401:4900:87f0::/44#_graph What sometimes confuses people is why there are multiple paths from a given ASN towards the originator ASN. Many people assume multiple paths exist for different prefixes only, and that is not true. Take e.g in the above route propagation graph AS3356 has a direct route to AS9498 as well as via AS2914, AS6939, AS6453, etc. And this kind of multiple paths is not limited just to AS3356 (which is run by three companies as of now - Lumen in North America, Colt in the EU and Cirion in South America). Notice GTT AS3257 is also learning it via Cogent AS174 as well as Tata Comm AS6453. Which is actually "best path" as determined by the BGP? Quick short answer: Both! Why does this happen? This kind of routing often happens when the other side is a large network with multiple routers doing eBGP with multiple other larger networks & not anywhere in the upstream path. Let's take the GTT AS3257 example first before coming to AS3356 case (as AS3356 has something more to it as well, which I will cover after this one). Let's query 2401:4900:87f0::/44 on Hurricane Electric's super-lg and restrict output with AS3257 in the path - output here Path 2 shows GTT AS3257 learning it from Cogent AS174 but path 4 shows it's learning it from Tata Comm AS6453. Both of these are "best paths" as determined by BGP in the respective routers that feed the routes. Path 2 via Cogent is being fed into route-views.chicago while path 4 is being fed into RIPE RIS RRC12 (DE-CIX, Frankfurt). Let's look at the GTT looking glass and trace to this route in the Chicago and Frankfurt router: GTT Chicago > 2401:4900:87f0::1 IPv6 traceroute to 2401:4900:87f0::1 HOST: cr1-chi1-re1 Loss% Snt Last Avg Best Wrst StDev 1. 2001:668:0:2:ffff:0