Summary

  • Linkova says her office’s 2019 IPv6-only guest network made a manager’s phone wait seven seconds. Troubleshooting pointed to a gap in the Neighbor Discovery state machine.
  • RFC 9131 lets a first-hop router learn a newly assigned IPv6 address from an unsolicited Neighbor Advertisement. Linkova says Android and several vendors implemented the idea; the RIPE transcript does not give a device-and-router test matrix.

Seven seconds was a protocol problem in a user’s hand

Seven seconds is an eternity when a phone is meant to join Wi-Fi. In a 2026 RIPE 93 talk, Jen Linkova recalled moving her office guest network to IPv6-only in 2019. Her manager complained that his phone took seven seconds to connect. Other users were unhappy too.

The delay did not come from a slow password prompt. Linkova and colleagues traced it to the Neighbor Discovery state machine. IPv6 hosts use Neighbor Discovery to find a router’s link-layer address and maintain reachability on the local link. A phone that has just received a new global IPv6 address can send traffic off-link through its default router. Yet that first-hop router may not have a Neighbor Cache entry for the phone’s new address.

RFC 9131 describes the awkward moment. The router may only start address resolution after return traffic arrives for the host. While it waits, the router keeps only a small number of packets in its queue; later packets can be dropped. The result is delay and packet loss at the point where a newly connected device tries to use the network.

Linkova carried the failure into the IETF. Her account says a draft was adopted after she raised the problem, Android and several vendors implemented the proposed change, and the eventual RFC appeared about two years later. She said the Android implementation arrived faster and that her manager stopped seeing the seven-second delay.

RFC 9131 gives hosts a way to notify first-hop routers when a new global IPv6 address is assigned: send an unsolicited Neighbor Advertisement. A router can then create a Neighbor Cache entry before the first return packet has to trigger discovery. The RFC also updates router behavior and describes how to handle existing, incomplete and missing cache entries. It was published in October 2021 as an IETF Standards Track document updating RFC 4861.

The useful part of Linkova’s story is the route from complaint to shared mechanism. She could have asked one vendor to patch one office. Instead, she says she wanted experts from different parts of the industry to test whether a change that helped her network could break someone else’s. The IETF review gave the problem a common document and a change multiple implementations could make.

An RFC does not tell us how many current phones and routers use the change. The RIPE transcript names Android and “a few vendors” but gives no product versions, packet traces or test counts. A public matrix linking client and router versions to Neighbor Advertisement handling and first-connection delay would show how broadly the seven-second fix travelled.

That is the distinction between a complaint and an Internet standard: the complaint supplies the failure; packets expose the mechanism; implementations show whether the repair left the meeting room.

Sources