Summary

  • Iliana Xygkou and Bryton Herdes used direct peering observations and an OTC-marked announcement to identify 15 ASes that stripped the route-leak prevention attribute. Their slides report missing OTC on 33.1% of unique IPv4 AS paths and 17% of unique IPv6 paths in that experiment.
  • The team contacted Arelion and GTT. The October NANOG slides say Arelion changed its configuration to preserve OTC while GTT still removed it. A newer direct retest would establish GTT's present state.

Fifteen networks ate the warning label. The route kept moving. At NANOG 98, Iliana Xygkou and Bryton Herdes showed what happens to a BGP safety rule when a network in the middle discards the very bit the next operator needs to enforce it.

The bit is Only to Customer, or OTC. RFC 9234 makes it an optional transitive path attribute. Once a route has been sent sideways to a peer or downward to a customer, the marker tells later networks it may travel only toward customers. Section 5 says an OTC value, once set, must remain unchanged. An intermediate AS that strips it removes that signal for everyone downstream.

The team's original slides take care over attribution. A distant path with OTC does not reveal whether the far network set it on egress or its neighbor supplied it on ingress. Direct peering narrows that ambiguity: if a route received from a peer carries OTC equal to that peer's AS number, the peer set it. The team then announced an OTC-marked route to peers and looked for paths that lost the attribute further along.

The result in the deck is 15 stripping ASes. It also reports missing OTC on 33.1% of unique IPv4 AS paths and 17% of unique IPv6 AS paths in its experiment. Those are path shares in this test, not shares of Internet traffic. The named confrontation comes one slide later. The team contacted two Tier-1 networks. Arelion, AS1299, promptly changed configurations to preserve the marker. GTT, AS3257, continued stripping it in the October presentation snapshot.

That makes the usual standards victory lap awkward. The RFC existed. One contacted operator fixed its running configuration; another still shed the signal. The deck does not publish a later GTT retest or a peer-by-peer raw dataset. A fresh tagged-route test through AS3257 would settle the present configuration. The October result already locates the decision: at the network that forwards the route, where an operator can preserve the attribute or erase it.

Sources: NANOG 98 session · original presentation · RFC 9234.