Summary

  • Thomas Holterbach's 27 October RIPE 93 presentation reports route-server BMP feeds from three IXPs. They expose stages a conventional looking glass can miss, including routes received before an inbound filter acts.
  • The view is only as broad as the feeds supplied. Operators decide which sessions and stages leave their routers; a participant feed cannot stand in for an entire exchange's route-server record.

A looking glass is a splendid name for a tool with blind spots. If a route no longer appears in its window, was it withdrawn by its sender, stopped at an inbound filter, beaten by another path or hidden by the collector's own view? Those are four different phone calls. A blank pane answers none of them.

At RIPE 93 on 27 October, Thomas Holterbach proposed putting a more revealing window behind the route server. His original slides report that Breizh-IX, EuroRhine-IX and Ouest.Network already send route-server BGP Monitoring Protocol, or BMP, feeds to the collection system he presented. One route server uses FRRouting and two use BIRD. All three feeds include received-route data. This is an early deployment, not an exchange-wide census.

BMP's trick is to keep the route's place in the queue attached to the observation. RFC 7854 distinguishes what a peer sent before inbound policy from what survived it. RFC 8671 adds the outbound view, and RFC 9069 covers the selected local table. The talk also describes peer-session changes and the update stream. One can ask whether a route arrived, passed a rule and became a candidate for onward distribution, instead of treating its absence from a public display as a confession by the sender.

The presenter contrasts that stream with familiar tools. A BGP Add-Path collection session sees routes that survived filtering. Polling route-server software can reveal more of the current state but loses much of the sequence between polls. The slides' disappearing-path scene is a teaching example, not a reported leak. It shows why a timestamped before-and-after view would shorten the argument over whose filter or session changed.

The deployment numbers also come with a map of their limits. The slides describe 60 BMP sessions from participating networks, offering views into about 200 sessions to route servers across 37 servers and about 1,000 bilateral sessions across 38 IXPs. Yet they explicitly say there is no route-server BMP feed from AMS-IX in this collection; participant feeds offer a partial view there. A dashboard that says “AMS-IX” without naming the participant and stage would borrow authority from a room it has not inspected.

Holterbach's deck says contributors can choose the BGP sessions and BMP stages they export, where their routers support the choice. That is the governance decision inside the engineering proposal. The same presentation notes the value of public investigation and the exposure of policy details to hostile observers. Better sight calls for an explicit sharing boundary, not a blanket assumption that every backstage camera belongs on the public screen.