--- title: Reuse a BGP AS Number Across Multiple Sites « BGP Labs description: This BGP lab exercise covers the scenario where multiple customer sites share the same BGP AS number when connecting to an MPLS/VPN service provider. The... canonical: https://daily.dev/posts/reuse-a-bgp-as-number-across-multiple-sites-bgp-labs-pzpfuiumn twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Reuse a BGP AS Number Across Multiple Sites « BGP Labs | daily.dev og:description: This BGP lab exercise covers the scenario where multiple customer sites share the same BGP AS number when connecting to an MPLS/VPN service provider. The... og:url: https://daily.dev/posts/reuse-a-bgp-as-number-across-multiple-sites-bgp-labs-pzpfuiumn og:image: https://api.daily.dev/og/posts/pZPFuIuMN.png og:image:alt: Reuse a BGP AS Number Across Multiple Sites « BGP Labs og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Reuse a BGP AS Number Across Multiple Sites « BGP Labs **[ipSpace.net Blog](https://daily.dev/sources/ipspace)** · 7 min read · 0 upvotes · 0 comments ## Summary This BGP lab exercise covers the scenario where multiple customer sites share the same BGP AS number when connecting to an MPLS/VPN service provider. The problem arises because BGP's built-in loop prevention drops updates that contain the router's own AS number in the AS path. The lab walks through diagnosing the issue using BGP update debugging on Cisco IOS and the 'show ip bgp neighbor' output on Arista EOS, then resolves it by configuring the 'allowas-in' knob on CE routers to disable AS-path loop prevention per neighbor. Lab topology uses netlab with CE/PE routers in AS65000 and AS65100 respectively. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why is BGP dropping routes when multiple sites share the same AS number? BGP's AS-path loop prevention logic drops incoming updates that contain the router's own AS number in the AS path. When two customer sites share the same AS number (e.g., AS65000) and connect through a provider, the provider reflects one site's prefix back to the other with AS65000 in the path — which the receiving CE router interprets as a loop and discards. On Cisco IOS, debug output shows 'DENIED due to: AS-PATH contains our own AS'. _Network engineers troubleshooting BGP route propagation across shared-AS sites track these patterns on daily.dev._ ### How do I fix BGP loop prevention blocking routes when two sites share the same AS number? Configure 'neighbor allowas-in' on each CE router's EBGP session toward the provider PE router. This per-neighbor knob disables AS-path-based loop prevention, allowing the CE to accept updates that contain its own AS number. After enabling it, refresh the BGP table with 'clear ip bgp soft in' or by resetting the EBGP session to the PE router. _Engineers deploying shared-AS BGP topologies find relevant configuration patterns and gotchas on daily.dev._ ### How can I tell if BGP is dropping routes due to AS path loop detection on Arista EOS? On Arista EOS, run 'show ip bgp neighbor' and look for the 'Inbound updates dropped by reason' section near the bottom. A counter labeled 'AS path loop detection' shows how many updates were silently discarded. Unlike Cisco IOS, Arista EOS does not support BGP update debugging, so this counter is the primary diagnostic signal available. _Arista EOS operators dealing with silent BGP drops share findings and workarounds on daily.dev._ ## Similar posts on daily.dev - [BGP-Free Core with SR-MPLS « ipSpace.net blog](https://daily.dev/posts/bgp-free-core-with-sr-mpls-ipspace-net-blog-h7kronzy3) · ipSpace.net Blog · 0 upvotes · 0 comments --- Tags: [#networking](https://daily.dev/tags/networking), [#bgp](https://daily.dev/tags/bgp) [View this post on daily.dev](https://daily.dev/posts/reuse-a-bgp-as-number-across-multiple-sites-bgp-labs-pzpfuiumn) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Reuse a BGP AS Number Across Multiple Sites « BGP Labs","url":"https://daily.dev/posts/reuse-a-bgp-as-number-across-multiple-sites-bgp-labs-pzpfuiumn","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/reuse-a-bgp-as-number-across-multiple-sites-bgp-labs-pzpfuiumn"},"datePublished":"2026-08-11T08:54:41.592Z","dateModified":"2026-08-11T09:15:34.244Z","description":"This BGP lab exercise covers the scenario where multiple customer sites share the same BGP AS number when connecting to an MPLS/VPN service provider. 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