Several users recently started receiving this Windows VPN error when connecting to a Meraki L2TP VPN: "The L2TP connection attempt failed because the security layer encountered a processing error during initial negotiations with the remote computer." The pre-shared key was verified, VPN profiles were rebuilt, network adapters were removed and reinstalled, and both the affected computers and home routers were rebooted. The issue was ultimately resolved by disabling IPv6 on the users' network adapters. Has anyone else encountered this with Meraki or other VPN clients, and is disabling IPv6 a reasonable long-term workaround?
3 Answers
Check the path MTU as well. Some VPN clients are very sensitive to packet size, and lowering the MTU can resolve negotiation or connection failures. IPv6 may change how packets are routed or fragmented, which could explain why disabling it appears to help.
Other clients, including FortiClient and SonicWall, have had similar IPv6-related behavior. Disabling IPv6 is a practical workaround when you need a quick fix, but for a long-term solution I’d verify firmware and client versions, inspect IPv6 and UDP/IPsec behavior on the affected networks, and test MTU settings before applying it everywhere.
I’ve seen this with several VPN clients and different employers. Disabling IPv6 often gets the connection working, but it may be masking an IPv6 compatibility or routing problem rather than fixing the underlying cause.
It usually affected only certain users or networks, not everyone in the organization. That made home-router and ISP differences seem likely.
I’d treat it as a targeted workaround rather than a blanket policy. If IPv6 is needed elsewhere, disabling it system-wide could create new connectivity problems.