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Treat-as-withdraw

Treat-as-withdraw is the BGP error-handling approach defined in RFC 7606 that revises the original RFC 4271 behavior for malformed UPDATE messages. Instead of tearing down the entire BGP session (which would disrupt all routes exchanged with that peer), the router silently withdraws only the specific route(s) affected by the malformed attribute.

Motivation

The original RFC 4271 specified that certain attribute errors MUST result in a NOTIFICATION message and session reset. For a large eBGP session carrying thousands of prefixes, resetting the session due to one malformed route is disproportionately destructive.

Application to First AS enforcement

When a router receives a route with a mismatched First AS, the correct behavior (per RFC 7606) is to treat the malformed AS_PATH as a route withdrawal — drop that specific prefix from the RIB without disrupting the BGP session.

However, Cloudflare's 2026 testing found that some networks still implement the pre-RFC 7606 behavior (session reset), making it unsafe to continuously advertise First AS-violating test routes without risking production traffic disruption. (Source: sources/2026-06-03-cloudflare-enforcing-the-first-as-in-bgp-as-paths)

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